WO2020022615A1 - Apparatus for measuring neutron ambient dose equivalent and method for measuring neutron ambient dose equivalent using thereof - Google Patents

Apparatus for measuring neutron ambient dose equivalent and method for measuring neutron ambient dose equivalent using thereof Download PDF

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Publication number
WO2020022615A1
WO2020022615A1 PCT/KR2019/004977 KR2019004977W WO2020022615A1 WO 2020022615 A1 WO2020022615 A1 WO 2020022615A1 KR 2019004977 W KR2019004977 W KR 2019004977W WO 2020022615 A1 WO2020022615 A1 WO 2020022615A1
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Prior art keywords
neutron
shell
epithermal
shielding material
moderator
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PCT/KR2019/004977
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French (fr)
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Jungho Kim
Hyeonseo PARK
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Korea Research Institute Of Standards And Science
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Publication of WO2020022615A1 publication Critical patent/WO2020022615A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T3/00—Measuring neutron radiation
    • G01T3/001—Spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/02—Dosimeters
    • G01T1/12—Calorimetric dosimeters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T3/00—Measuring neutron radiation
    • G01T3/04—Measuring neutron radiation using calorimetric devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00—Details of radiation-measuring instruments

Definitions

  • the present invention relates to an apparatus and method for measuring a neutron ambient dose equivalent, and more particularly, to an apparatus for measuring a neutron ambient dose equivalent which matches response of the apparatus for measuring a neutron ambient dose equivalent with a neutron fluence-ambient dose equivalent conversion coefficient curve in a wide energy range from a thermal neutron to a fast neutron and a method for measuring a neutron ambient dose equivalent using the same.
  • a neutron ambient dose equivalent has about 100 times difference depending on neutron energy, and thus, in principle, only when a value of the neutron energy is known, it is possible to accurately calculate the neutron ambient dose equivalent.
  • a change in the neutron ambient dose equivalent depending on the neutron energy is given by the neutron fluence-ambient dose equivalent conversion coefficient (thick black solid line in FIG. 1), and if the neutron fluence indicating the number of neutrons per unit area depending on the neutron energy is known, it is possible to obtain the neutron ambient dose equivalent by multiplying the neutron fluence by the neutron fluence-ambient dose equivalent conversion coefficient.
  • a neutron ambient dose equivalent meter usually is a neutron measuring instrument which measures a neutron ambient dose equivalent rate for a thermal neutron to a degree at which neutron kinetic energy is about 0.025eV which constitute a Maxwell-Boltzmann distribution to a fast neutron up to about 20 MeV.
  • the neutron ambient dose equivalent meter usually has a shape in which a thermal neutron detector is inserted into a spherical moderator having a diameter of about 20 cm to 25 cm or a cylindrical moderator having a diameter and a height of about 20 cm to 25 cm.
  • 6 Li, 10 B, and He 3 react well with neutrons and are widely used in the neutron detector.
  • Response(response of 6 Li, 10 B, and He 3 ) is inversely proportional to a neutron speed. Therefore, since the thermal neutron response is largest, as proposed in Korean Patent No. 10-1281083, an apparatus including a polyethylene Bonner sphere of various sizes and a thermal neutron detector is widely used as a neutron measuring instrument.
  • neutrons incident on the neutron ambient dose equivalent meter are decelerated to the thermal neutrons in the moderator, and a count rate is measured by the thermal neutron detector inserted thereinto. Since the neutron ambient dose equivalent meter cannot measure the incident neutron energy, the measured count rate is calibrated at the reference neutron ambient dose equivalent rate to obtain a ratio of the count rate and the neutron ambient dose equivalent rate, and the obtained ratio is applied and thus indicated by the neutron ambient dose equivalent rate.
  • FIG. 1 shows the response of neutron ambient dose equivalent meters (LB6411 I, leake remmeter, Eberline NRD, Studsvik2202D in FIG. 1) which is already developed and neutron fluence-ambient dose equivalent conversion coefficient curve (thick black solid line in FIG. 1).
  • neutron ambient dose equivalent meters LB6411 I, leake remmeter, Eberline NRD, Studsvik2202D in FIG. 1
  • neutron fluence-ambient dose equivalent conversion coefficient curve thin black solid line in FIG. 1
  • most of the neutron ambient dose equivalent meters are generally matched well in a 1 MeV range, but largely have 10 times or more difference in an epithermal neutron range and a thermal neutron range having a neutron energy range from 1 eV to 10 keV. Therefore, in the already developed neutron ambient dose equivalent meter, a measured value of the neutron ambient dose equivalent meter differs from an actual neutron ambient dose equivalent rate depending on a neutron energy distribution of a neutron field to be measured.
  • the neutron energy to be usually measured is in a very large energy range, so neutron dosimeters need to be operated at meV to several tens of MeV to be able to accurately measure the neutron ambient dose equivalent rate.
  • the response depending on the neutron energy needs to be the same as the neutron fluence-ambient dose equivalent conversion coefficient.
  • the shape of the neutron energy spectrum greatly differs depending on the neutron field, and therefore development of a neutron ambient dose equivalent meter using a representative neutron spectrum has a long way to go.
  • the neutron fluence-ambient dose equivalent conversion coefficient has a sharp change depending on the neutron energy in the energy range from 10 keV to 1 MeV, but it is difficult to develop the neutron ambient dose equivalent meter having the same sharp change in response, and therefore a neutron ambient dose equivalent meter having satisfactory performance has not yet been developed.
  • the neutron ambient dose equivalent meter basically has a structure in which neutrons are decelerated and converted into thermal neutrons and then measured by the thermal neutron detector inserted into the center thereof. Since a polyethylene having a diameter of 20 cm or more is usually used in order to decelerate neutrons having a neutron energy of 1 MeV or more, the neutron ambient dose equivalent meter is heavy as a mass of about 9 kg.
  • An object of the present invention is to provide an apparatus for measuring a neutron ambient dose equivalent which matches response depending on neutron energy in a wide energy range from a thermal neutron to a fast neutron with a neutron fluence-ambient dose equivalent conversion coefficient curve and a method for measuring a neutron ambient dose equivalent using the same.
  • an apparatus for measuring a neutron ambient dose equivalent includes: a thermal neutron detector; a first neutron moderator shell which encloses the thermal neutron detector; an epithermal neutron shielding material shell which encloses the first neutron moderator shell; a second neutron moderator shell which encloses the epithermal neutron shielding material shell; and an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the epithermal neutron shielding material shell .
  • the air layer may penetrate through the epithermal neutron shielding material shell, and may have one end located inside the first neutron moderator shell.
  • the second neutron moderator shell may have a spherical, polyhedral, cylindrical, or polygonal prism shape.
  • the air layer may have a hollow disk shape or a hollow polygonal plate shape.
  • the open aperture formed on the surface of the second neutron moderator shell by the air layer may form a closed curve or a closed curved line.
  • the epithermal neutron shielding material shell may have a shape of a sphere, a polyhedron, a cylinder, or a polyprism.
  • the apparatus for measuring a neutron ambient dose equivalent may further include a shielding plate which contacts the epithermal neutron shielding material shell along an outer circumference of the epithermal neutron shielding material shell, covers at least a part of the air layer, and shields an epithermal neutron introduced into the air layer through the second neutron moderator shell.
  • the epithermal neutron shielding plate may include a first shielding plate and a second shielding plate facing each other with the air layer interposed therebetween.
  • the first neutron moderator shell and the second neutron moderator shell may be formed of polyethylene, and the epithermal neutron shielding material shell may be formed of boron carbide.
  • the apparatus for measuring a neutron ambient dose equivalent may satisfy the following dimension 1.
  • R2 0.25R1 to 0.8R1
  • R3 0.05R2 to 0.6R2
  • T1 0.05R1 to 0.3R1
  • R1 is a shortest distance from the center of the thermal neutron detector to a outer shell(outer surface, outer circumference) of the second neutron moderator shell
  • R2 is a shortest distance from the center of the thermal neutron detector to a inner shell(inner surface, inner circumference) of the epithermal neutron shielding material shell
  • R3 is a shortest distance from the center of the thermal neutron detector to one end of the air layer located at the inside of the epithermal neutron shielding material shell
  • T1 is a thickness of the second neutron moderator shell
  • D1 is a width of the open aperture.
  • the thickness and the width of the shielding plate may satisfy the following dimension 2.
  • T2 0.02R1 to 0.2R1
  • T2 is a thickness of the shielding plate
  • W1 is a width of the shielding plate
  • R1 is a shortest distance from the center of the thermal neutron detector to an outer shell of the second neutron moderator shell
  • R4 is a shortest distance from the open aperture of the second neutron moderator shell to an outer shell of the epithermal neutron shielding material shell.
  • an apparatus for measuring a neutron ambient dose equivalent includes: a neutron moderator sphere in which a thermal neutron detector is located; an epithermal neutron shielding material shell which is located inside the neutron moderator sphere to enclose a detector with being spaced apart from the thermal neutron detector; a hollow disk-shaped air layer which forms an open aperture along a circumference of the neutron moderator sphere, penetrates through the epithermal neutron shielding material shell, and has a thermal neutron detector located at a center of the hollow; and a shielding plate which contacts the epithermal neutron shielding material shell along an outer circumference of the epithermal neutron shielding material shell and covers at least a part of an air layer to shield an epithermal neutron introduced into the air layer through the second neutron moderator shell.
  • the apparatus for measuring a neutron ambient dose equivalent has an advantage in that the neutron response of the apparatus substantially matches the neutron fluence-ambient dose equivalent conversion coefficient in a wide energy range from 0.025 eV to 20 MeV.
  • the apparatus for measuring a neutron ambient dose equivalent is lightweight and has good mobility as it can measure the neutron energy in a wide energy range from 0.025 eV to 20 MeV based on a single neutron moderator sphere.
  • the apparatus for measuring a neutron ambient dose equivalent can monitor the neutron ambient dose equivalent in real time.
  • FIG. 1 is a diagram showing a response and neutron fluence-ambient dose equivalent conversion coefficient of the conventional apparatus for measuring a neutron ambient dose equivalent.
  • FIG. 2 is a perspective view of an apparatus for measuring a neutron ambient dose equivalent according to an embodiment of the present invention.
  • FIG. 3 is a cross-sectional view taken along line A-A in the perspective view of FIG. 2.
  • FIG. 4 is another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
  • FIG. 5 is a cross-sectional view taken along line A-A in the perspective view of FIG. 4.
  • FIG. 6 is still another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
  • FIG. 7 is still another perspective view of an apparatus for measuring a neutron ambient dose equivalent according to an embodiment of the present invention.
  • FIG. 8 is still another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
  • FIG. 9 is a cross-sectional view taken along line A-A in the perspective view of FIG. 8.
  • FIG. 10 is another cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
  • FIG. 11 is a view showing only a shielding plate in FIG. 10.
  • FIG. 12 is still another cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
  • FIG. 13 is a view separately showing only the shielding plate in FIG. 12.
  • FIG. 14 is a diagram showing the response and neutron fluence-ambient dose equivalent conversion coefficient of the conventional apparatus for measuring a neutron ambient dose equivalent including a polyethylene moderator sphere in which a thermal neutron detector is located at a center of the sphere.
  • FIG. 15 is a diagram showing the response and the neutron fluence-ambient dose equivalent conversion coefficient curve depending on the neutron energy of the apparatus including the polyethylene moderator sphere where the thermal neutron detector is located at the center of the sphere and a boron carbide epithermal neutron shielding material shell embedded in the polyethylene moderator sphere so that the thermal neutron detector is located at a center therein.
  • FIG. 16 is a diagram showing the response and the neutron fluence-ambient dose equivalent conversion coefficient curve depending on the neutron energy of the apparatus including the polyethylene moderator sphere where the thermal neutron detector is located at the center of the sphere, the boron carbide epithermal neutron shielding material shell embedded in the polyethylene moderator sphere so that the thermal neutron detector is located at a center therein, and an air layer which forms an open aperture in the moderator sphere and penetrates through the epithermal neutron shielding material shell.
  • FIG. 17 is a diagram showing the response and the neutron fluence-ambient dose equivalent conversion coefficient curve depending on the neutron energy of the apparatus including the polyethylene moderator sphere where the thermal neutron detector is located at the center of the sphere, the boron carbide epithermal neutron shielding material shell embedded in the polyethylene moderator sphere so that the thermal neutron detector is located at a center therein, the air layer which forms an open aperture in the moderator sphere and penetrates through the epithermal neutron shielding material shell, and a shielding plate which contacts a circumference of an outer surface of the epithermal neutron shielding material shell and covers the air layer adjacent to the outer surface of the epithermal neutron shielding material shell.
  • An apparatus for measuring a neutron ambient dose equivalent includes: a thermal neutron detector; a first neutron moderator shell which encloses the thermal neutron detector; an epithermal neutron shielding material shell which encloses the first neutron moderator shell; a second neutron moderator shell which encloses the epithermal neutron shielding material shell; and an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the epithermal neutron shielding material shell.
  • the first neutron moderator shell may be a shell containing a first neutron moderator which converts a neutron into a thermal neutron
  • the second neutron moderator shell may be a shell containing a second neutron moderator shell which converts a neutron into a thermal neutron
  • the epithermal neutron shielding material shell may be a shell containing an epithermal neutron shielding material which absorbs and/or removes an epithermal neutron.
  • the first neutron moderator shell and the second neutron moderator shell may each serve to reduce a neutron to convert the neutron into the thermal neutron
  • the epithermal neutron shielding material shell may serve to remove the epithermal neutron introduced into the thermal neutron detector through the second neutron moderator shell to reduce the response of the measuring apparatus in an energy range from several keV to 1 MeV.
  • the air layer which forms the open aperture along the circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the neutron shielding material shell may serve to improve the response of the measuring apparatus in the energy range of several keV or less which is excessively reduced by the epithermal neutron shielding material shell provided to shield the epithermal neutron, and may serve as an epithermal neutron moving passage through which the epithermal neutron passes through the second neutron moderator shell and an epithermal neutron shielding material shell range and is directly introduced into the first neutron moderator shell contacting the detector.
  • the air layer may be a hollow disk or a hollow polygonal plate depending on the shape of the second neutron moderator shell, and the thermal neutron detector enclosed by the neutron moderator derived from the first neutron moderator shell may be located at the center of the hollow.
  • the apparatus for measuring a neutron ambient dose equivalent has a basic detection structure for detecting a thermal neutron by converting the neutron into the thermal neutron by the neutron moderator.
  • FIG. 1 shows that when the neutron energy is measured by converting a neutron into a thermal neutron using a neutron moderator, the response well matches the neutron fluence-ambient dose equivalent conversion coefficient curve near the 1 MeV, but the excessively high response appears in the energy range lower than 1 MeV.
  • the apparatus for measuring a neutron ambient dose equivalent converts a neutron into a thermal neutron by the neutron moderator and measures the thermal neutron, and may have very similar response to the neutron fluence-ambient dose equivalent conversion coefficient curve in a wide energy range from a thermal neutron to a fast neutron by lowering an excessively high response against the neutron fluence-ambient dose equivalent conversion coefficient curve in the epithermal neutron-thermal neutron energy range by the epithermal neutron shielding material interposed between the neutron moderators and improving, by using the air layer, the response in the thermal neutron (and near) energy range excessively lowered by the epithermal neutron shielding material.
  • the present applicant found that the response in the energy range of several keV or less is not improved as much as desired even when a size, a shape, and an arrangement of channels are different only by pore channels (pore channels formed in the direction of the detector from the surface of the outermost shell with opened pore channels) such as a bar or a cylinder and found that the response in the energy range of several keV or less is insignificant but the epithermal neutron shielding material shell is inactivated by a plurality of channels spaced apart from each other and the response in the energy range from several keV to 1 MeV is excessively increased.
  • pore channels pore channels formed in the direction of the detector from the surface of the outermost shell with opened pore channels
  • an open aperture is formed along the circumference of the second neutron moderator shell, that is, an opened structure is formed on the surface of the second neutron moderator shell to enclose the circumference of the second neutron moderator shell and the opened structure is formed in a layer form so that the opened structure on the surface of the second neutron moderator shell penetrates through the epithermal neutron shielding material shell and extends to the inside of the first neutron moderator shell, it is possible to improve the response until the response in the energy range of several keV or less substantially matches the neutron fluence-ambient dose equivalent conversion coefficient curve.
  • the apparatus for measuring a neutron ambient dose equivalent includes: a thermal neutron detector; a first neutron moderator shell which encloses the thermal neutron detector; an epithermal neutron shielding material shell which encloses the first neutron moderator shell; a second neutron moderator shell which encloses the epithermal neutron shielding material shell; and an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the first neutron moderator shell (in the first neutron moderator shell).
  • the shape (outer shape) of the second neutron moderator shell determines the overall shape of the apparatus for measuring a neutron ambient dose equivalent.
  • the second neutron moderator shell may have a shape of a sphere, a polyhedron, a cylinder, or a polyprism(polygonal column).
  • Examples of the polyhedron may include a regular hexahedron, a regular octahedron, a cut regular octahedron, a regular dodecahedron, a cut regular dodecahedron, a regular tetradodehedron, a cut regular tetradodehedron, a regular icosahedron, a cut regular icosahedron, and the like
  • examples of the polyprism may include a quadrangular (regular tetragonal to rectangular) prism, a pentagonal prism, a hexagonal prism, an octagonal prism, a decagonal prism, a dodecagonal prism and the like.
  • the second neutron moderator shell may have a sphere, a polyhedron having a regular dodecahedron or more, a cylinder, or a polyprism of a pentagonal prism(pentagonal column) or more, but the shape of the second neutron moderator shell is not limited thereto.
  • Forming the open aperture along the circumference of the second neutron moderator shell may mean that the open aperture forms a closed line (closed band when considering the width of the open aperture) along the circumference of the second neutron moderator shell.
  • the shape of the closed line may correspond to a cross-sectional shape of the second neutron moderator shell.
  • the shape of the closed line may be a closed curve or a closed curved line.
  • the open aperture may be a shape of the closed curve
  • the second neutron moderator shell is a shape of a polyhedron or a polyprism
  • the open aperture may be a shape of a closed curved line
  • the shape (outer shape) of the epithermal neutron shielding shell may be a shape in which the epithermal neutron shielding shell may enclose the detector with being spaced apart from the detector by the first neutron moderator shell.
  • the shape of the epithermal neutron shielding material shell may have a shape of the sphere, a polyhedron, a cylinder, or a polyprism, separately of the second neutron moderator shell.
  • the polyhedron may include a regular hexahedron, a regular octahedron, a cut regular octahedron, a regular dodecahedron, a cut regular dodecahedron, a regular tetradodehedron, a cut regular tetradodehedron, a regular icosahedron, a cut icosahedron, and the like
  • a polyprism may include a quadrangular (regular tetragonal to rectangular) prism, a pentagonal prism, a hexagonal prism, an octagonal prism, a decagonal prism, a dodecagonal prism and the like.
  • the second neutron moderator shell may have a sphere, a polyhedron having a regular dodecahedron or more, a cylinder, or a polyprism of a pentagonal prism or more, but the shape of the second neutron moderator shell is not limited thereto.
  • the epithermal neutron shielding material shell may have a predetermined thickness (uniform thickness).
  • the shape of the epithermal neutron shielding material shell and the above-mentioned shell including the epithermal neutron shielding material shell are based on the outer shape of the shell.
  • the outer shape of the other shell (shell B) which is located in the outer direction of one shell and encloses one shell (shell A) may have various shapes such as the shapes of the sphere, the polyhedron, the cylinder, or the polyprism as described above, but it goes without saying that an inner shape of the other shell (shell B) has a shape corresponding to the outer shape of one shell (shell A) to adhere to the one shell without forming an unintended gap, so the other shell (shell B) can enclose the one shell (shell A).
  • the first neutron moderator shell may be a form that can fill the space between the epithermal shielding material shell and the detector.
  • the shape (outer shape) of the first neutron moderator shell may correspond to the inner shape of the epithermal shielding material shell, and may have a shape corresponding to the outer shape of the epithermal neutron shielding material shell as the thickness of the shielding material shell is constant.
  • the first neutron moderator shell may have the sphere, the polyhedron, the cylinder, or the polyprism, and may have a shape corresponding to the outer shape (or inner shape) of the epithermal neutron shielding material shell.
  • the first neutron moderator shell when the shape of the epithermal neutron shielding material shell is a spherical shape, the first neutron moderator shell may be a sphere in which the detector is located. As another specific example, when the shape of the epithermal neutron shielding material shell is a cylinder, the first neutron moderator shell may have the shape of the cylinder in which the detector is located. As still another specific example, when the shape of the epithermal neutron shielding material shell is a cylinder, the first neutron moderator shell may have the shape of the octagonal prism in which the detector is located.
  • the thermal neutron detector may be located at the center of the first neutron moderator shell, but the location of the thermal neutron detector is not limited thereto.
  • the thermal neutron detector any detector known to be used to detect thermal neutrons in the field of measuring the neutron ambient dose equivalent can be used.
  • the thermal neutron detector may be a BF 3 neutron proportional counter, a He 3 neutron proportional counter or the like, but is not limited thereto, and an active thermal neutron detector capable of transmitting a thermal neutron measurement signal in real time may be used.
  • the thermal neutron detector may have a spherical to cylindrical shape, but it goes without saying that the present invention can not be limited to the specific form of the thermal neutron detector.
  • the second neutron moderator shell, the epithermal neutron shielding material shell, the first neutron moderator shell, and the closed line (a closed band when considering the thickness of the air layer) which is an aperture portion formed on the second neutron moderator shell by the air layer may have a concentric structure, and the thermal neutron detector may be located at a center thereof, but they are not necessarily limited to this structure.
  • the measuring apparatus can include a single thermal neutron detector, which refers to that the measuring apparatus according to the present invention which is the single thermal neutron detector can confirm that the response of the apparatus matches the neutron fluence-ambient dose equivalent conversion coefficient curve in a wide range from 0.025 eV to 20 MeV. Therefore, the detector of the present invention can be constituted as the single thermal neutron detector due to the superiority of the present invention, but it should not be interpreted as excluding the case where two or more thermal neutron detectors are provided.
  • the apparatus for measuring a neutron ambient dose equivalent may further include a predetermined signal line for transmitting a measured signal output from the thermal neutron detector to the outside of the apparatus, and it goes without saying that the first neutron moderator shell, the epithermal neutron shielding material shell, and the second neutron moderator shell may be provided with a drawing-out hole for drawing-out a signal line 101 of the thermal neutron detector to the outside of the apparatus.
  • the apparatus for measuring a neutron ambient dose equivalent may further include a calculation unit which receives the measured signal output from the thermal neutron detector through the signal line and calculates the neutron energy based on the number of neutrons (thermal neutrons) counted by the thermal neutron detector and an output unit which outputs (including a display) the neutron energy calculated by the calculation unit.
  • FIG. 2 is a perspective view of an apparatus for measuring a neutron ambient dose equivalent according to an embodiment of the present invention
  • FIG. 3 is a cross-sectional view taken along line A-A in the perspective view of FIG. 2.
  • FIGS. 2 and 3 show examples in which a second neutron moderator shell 400, an epithermal neutron shielding material shell 300, and a first neutron moderator shell 200 all have a spherical shape, a thermal neutron detector 100 is located at the center of the sphere of the first neutron moderator shell 200 which has a spherical shape, and a hollow disk-shaped air layer 500 is formed.
  • the air layer 500 forms a ring-shaped open aperture 501 along the circumference of the second neutron moderator shell 400, extends from the open aperture 501, penetrates through the epithermal neutron shielding material shell 300, and extends so that one end 502 is located inside the first neutron moderator shell 200 (inside the first neutron moderator), such that the air layer 500 may have a hollow disk shape.
  • an outer surface of a plate forms the open aperture 501 on the second neutron moderator shell 400 and an inner surface (hollow surface) of the plate may enclose the thermal neutron detector 100 with being spaced apart from the thermal neutron detector 100.
  • FIGS. 2 and 3 show the examples in which a hollow of the hollow disk-shaped air layer 500 has a circular shape, but the shape of hollow in the hollow disk-shaped air layer is not necessarily limited thereto.
  • the hollow in the hollow plate-shaped air layer may have any shape such as a square, a pentagon, a hexagon, and an octagon as long as the air layer can enclose the thermal neutron detector 100 with being spaced apart from the thermal neutron detector 100.
  • FIG. 4 is another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention
  • FIG. 5 is a cross-sectional view taken along line A-A in the perspective view of FIG. 4.
  • FIGS. 4 and 5 show examples in which each of the second neutron moderator shell 400, the epithermal neutron shielding material shell 300, and the first neutron moderator shell 200 is a hexagonal prism shape and a hollow hexagonal plate-shaped air layer 500 is formed.
  • FIGS. 4 and 5 show examples in which the thermal neutron detector 100, the first neutron moderator shell 200, the epithermal neutron shielding material shell 300, and the hollow hexagonal plate-shaped air layer 500 all have a concentric structure with respect to a longitudinal center line of the hexagonal prism (second neutron moderator shell).
  • FIG. 6 is another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
  • FIG. 6 is an example in which the second neutron moderator shell 400, the epithermal neutron shielding material shell 300, and the first neutron moderator shell 200 all have an octagonal prism shape, and the thermal neutron detector 100, the first neutron moderator shell 200, and the epithermal neutron shielding material shell 300 all have a concentric structure with respect to a longitudinal center line of the octagonal prism which is the second neutron moderator shell 400.
  • the air layer 500 forms the open aperture 501 of the closed line along the circumference of the second neutron moderator shell 400, the shape of the air layer may be changed depending on the shape of the second neutron moderator shell.
  • FIG. 6 is an example in which the second neutron moderator shell 400, the epithermal neutron shielding material shell 300, and the first neutron moderator shell 200 all have an octagonal prism shape
  • the air layer 500 may have the hollow octagonal plate shape as the second neutron moderator shell 400 has an octagonal prism shape.
  • FIG. 6 shows an example in which the hollow of the octagonal plate is a circle, as described above, the shape of the hollow may be a polygonal shape including a circle, a square, a pentagon, a hexagon, an octagon, and the like, independent of the shape of the plate.
  • FIG. 7 is a perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
  • FIG. 7 shows an example in which the second neutron moderator shell 400 has a cylindrical shape, the epithermal neutron shielding material shell 300 has a hexagonal prism shape, and the first neutron moderator shell 200 has a hexagonal prism shape, and as shown in FIG. 2, the hollow disk-shaped air layer 500 is formed.
  • FIG. 7 shows an example in which the thermal neutron detector 100, the first neutron moderator shell 200, and the epithermal shielding material shell 300 have a concentric structure with respect to the longitudinal center line of the cylinder (second neutron moderator shell).
  • FIG. 8 is a perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention
  • FIG. 9 is a cross-sectional view taken along line A-A in the perspective view of FIG. 8.
  • FIGS. 8 and 9 show examples in which the second neutron moderator shell 400 has a spherical shape, the epithermal neutron shielding material shell 300 has a hexagonal prism shape, and the first neutron moderator shell 200 has a hexagonal prism shape, shows an example in which the thermal neutron detector 100, the first neutron moderator shell 200, and the epithermal neutron shielding material shell 300 all have a concentric structure with respect to a center line N-S of the sphere connecting between a top point N and a bottom point S of the sphere, and shows an example in which the hollow disk-shaped air layer 500 is formed.
  • the air layer 500 may have the hollow disk shape or the hollow polygonal plate shape depending on the shape of the second neutron moderator shell, and the shape of the hollow may be a polygonal shape including a circle, a square, a pentagon, a hexagon, an octagon, and the like, independent of the shape of the plate.
  • a "one end" which penetrates through the epithermal shielding material shell and is located inside (in) the first neutron moderator shell means that the hollow disk or the hollow polygonal plate is located inside (in) the first neutron moderator shell, and one end of the air layer may mean a hollow surface of the hollow.
  • the apparatus for measuring a neutron ambient dose equivalent may further include a shielding plate which contacts the epithermal neutron shielding material shell along the outer circumference of the epithermal neutron shielding material shell together with the thermal neutron detector, the first neutron moderator shell, the epithermal neutron shielding material shell, and the second neutron moderator shell, and the air layer, and covers at least a part of the air layer to shield the epithermal neutron introduced into the air layer through the second neutron moderator shell.
  • covering the air layer with the shielding plate means that the shielding plate is located between the air layer and the second neutron moderator shell.
  • the air layer can serve as a moving (introduction) passage for the thermal neutron into which the thermal neutron can be directly introduced into the first neutron moderator shell, such that the response of the measuring apparatus in the energy range of several keV or less can be improved.
  • the shielding plate may serve to fundamentally prevent the epithermal neutron from being introduced from the second neutron moderator shell into the air layer. It is possible to stably maintain the response in the energy range from several keV to 1 MeV which is lowered by the epithermal neutron shielding material shell simultaneously with improving the response in the energy range of several keV or less by the air layer due to the shielding of the epithermal neutron of the shielding plate.
  • the shielding plate includes a first shielding plate which can shield the epithermal neutron introduced from an upper part thereof into the air layer through the second neutron moderator shell and a second shielding plate which can shield the epithermal neutron from a lower part thereof into the air layer through the second neutron moderator shell.
  • the shielding plate may include the first shielding plate and the second shielding plate facing each other with the air layer interposed therebetween, and each of the first shielding plate and the second shielding plate may contact the epithermal neutron shielding material shell along the outer circumference of the epithermal neutron shielding material shell and cover at least a part of the air layer.
  • FIG. 10 is a cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent shown in FIG. 2 which further includes shield plates 610 and 620
  • FIG. 11 is a perspective view separately showing only the first shielding plate 610 and the second shielding plate 620 facing each other with being spaced apart from each other by a width of an open aperture (D1: thickness of the air layer) by the air layer 500 in FIG. 10.
  • FIG. 12 is a cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent shown in FIG. 8 which further includes shield plates 610 and 620
  • FIG. 13 is a perspective view separately showing only the first shielding plate 610 and the second shielding plate 620 facing each other with being spaced apart from each other by a width (D1: thickness of the air layer) of an open aperture by the air layer 500 in FIG. 12.
  • the shielding plate may include the first shielding plate 610 and the second shielding plate 620 which cover the air layer 500 provided on upper and lower parts thereof, respectively.
  • the first shielding plate 610 and the second shielding plate 620 are spaced apart from each other by the air layer interposed therebetween, and both the first shielding plate 610 and the second shielding plate 620 may contact the epithermal neutron shielding material shell 300 near a through region through which the air layer penetrates and enclose the epithermal neutron shielding material shell 300.
  • the shielding plate contacts the epithermal neutron shielding material shell 300 to enclose the epithermal neutron shielding material shell 300 and covers at least a part of the air layer 500, such that the shielding plate may have a hollow plate shape.
  • the shape of the hollow shielding plate may be a hollow disk shape or a hollow polygonal plate shape, and examples of the hollow polygonal plate may include a square, a pentagon, a hexagon, an octagon, and the like.
  • the size and shape of the hollow in the shielding plate having the hollow disk or the hollow polygonal plate shape may correspond to the size and shape of the epithermal neutron shielding material shell (see FIGS. 11 and 13).
  • how much the air layer is covered with the shielding plate can be controlled by the width of the hollow shielding plate.
  • the first shielding plate 610 and the second shielding plate 620 may each be the hollow disk shape having the circular hollow.
  • the first shielding plate 610 and the second shielding plate 620 may each have the hollow octagonal plate shape having an octagonal hollow. That is, the size and shape of the hollow shielding plate may correspond to the size and shape of the cross section of the epithermal neutron shielding material shell based on the surface penetrated by the air layer.
  • FIGS. 10 and 12 show examples in which the width of the shielding plate is smaller than the shortest distance from the open aperture located on the surface (outer surface) or the surface of the second neutron moderator shell 400 to the surface (outer surface) of the epithermal neutron shielding material shell to cover a part of the air layer located between the epithermal neutron shielding material shell and the second neutron moderator shell, but the present invention is not limited thereto, and it goes without saying that the shielding plate may completely cover the air layer located between the epithermal neutron shielding material shell and the second neutron moderator shell.
  • FIGS. 10 and 12 show the examples in which the first shielding plate and the second shielding plate have the same size and shape as each other, but the present invention is not limited thereto, and it goes without saying that the first shielding plate which is the hollow disk and the second shielding plate which is the hollow polygonal plate or the first shielding plate and the second shielding plate which have different widths and are the hollow disk, and the like may have different shapes and sizes if necessary.
  • any material known to convert a neutron into a thermal neutron may be used, and in detail, a representative example may be polyethylene, but the present invention is not limited to the specific neutron moderator material.
  • the epithermal shielding material of the epithermal neutron shielding material shell any material known to absorb and remove the epithermal neutron may be used, and the specific and representative example may be boron carbide (B 4 C), but the present invention is not limited to the specific epithermal neutron shielding material.
  • the conventional measuring apparatus which converts a neutron into the thermal neutron using the neutron moderator and measures the thermal neutron with a thermal neutron detector
  • the response of the apparatus matches the neutron fluence-ambient dose equivalent conversion coefficient curve in the vicinity of 1 MeV, but as the example shown in FIG. 1, the conventional measuring apparatus has the excessively large response against the neutron fluence-ambient dose equivalent conversion coefficient in an energy range of 1 MeV or less.
  • the response in the range from several keV to 1 MeV may substantially match the neutron fluence-ambient dose equivalent conversion coefficient by the epithermal neutron shielding material shell, and the response in the range of several keV or less which is excessively lowered by the epithermal neutron shielding material shell may be improved by the air layer to make the response of the apparatus substantially match the neuron fluence-ambient dose equivalent conversion coefficient even in the range of several keV or less.
  • the response in the range from several keV to 1 MeV may be kept stable to substantially match the neutron fluence-ambient dose equivalent conversion coefficient, by the shielding plate that prevents the thermal neutron from being introduced into the air layer even when the air layer is provided.
  • the apparatus for measuring a neutron ambient dose equivalent may satisfy the following dimension 1 and preferably satisfy the following dimension 1 and dimension 2.
  • R2 0.25R1 to 0.8R1, specifically 0.3R1 to 0.6R1
  • R3 0.05R2 to 0.6R2, specifically 0.15R2 to 0.5R2
  • T1 0.05R1 to 0.3R1, specifically 0.05R1 to 0.2R1
  • D1 0.01R1 to 0.05R1, specifically 0.02R1 to 0.05R1
  • R1 is the shortest distance from the center of the thermal neutron detector to the outer shell of the second neutron moderator shell
  • R2 is a shortest distance from the center of the thermal neutron detector to a inner shell(inner surface, inner circumference) of the epithermal neutron shielding material shell
  • R3 is the shortest distance from the center of the thermal neutron detector to one end of the air layer located on the inside (in the first neutron moderator shell) of the neutron shielding material shell
  • T1 is the thickness of the second neutron moderator shell
  • D1 is the width of the open aperture (thickness of the air layer).
  • T2 0.02R1 to 0.2R1, specifically 0.02R1 to 0.1R1
  • W1 0.2R4 to 0.8R4, specifically 0.2R4 to 0.6R4
  • T2 is the thickness of the shielding plate
  • W1 is the width of the shielding plate
  • R1 is the shortest distance from the center of the thermal neutron detector to the outer shell of the second neutron moderator shell
  • R4 is the shortest distance from the open aperture of the second neutron moderator shell to the outer shell of the epithermal neutron shielding material shell.
  • R1 may be 9.5 cm to 12.7 cm, and the present invention is not necessarily limited to the above-mentioned specific values.
  • An apparatus for measuring a neutron ambient dose equivalent includes: a neutron moderator sphere which has a thermal neutron detector located therein; an epithermal neutron shielding material shell which is located inside the neutron moderator sphere to enclose a detector with being spaced apart from the thermal neutron detector; a hollow disk-shaped air layer which forms an open aperture along a circumference of the neutron moderator sphere, penetrates through the epithermal neutron shielding material shell, and has a thermal neutron detector located at a center of the hollow; and a shielding plate which contacts the epithermal neutron shielding material shell along a circumference of an outer side of the epithermal neutron shielding material shell and covers at least a part of an air layer to shield an epithermal neutron introduced into the air layer through the second neutron moderator shell.
  • the apparatus for measuring a neutron ambient dose equivalent corresponds to the neutron modulator sphere having the configuration in which the first neutron moderator shell and the second neutron modulator shell are integrated, not the configuration in which the first neutron moderator shell and the second neutron modulator shell are separated from each other in the apparatus for measuring a neutron ambient dose equivalent described above, and corresponds to the case in which the epithermal neutron shielding material shell is inserted into the neutron moderator sphere.
  • the thermal neutron detector, the epithermal neutron shielding material shell, the neutron moderator, the air layer, and the shielding plate are similar to or the same as the thermal neutron detector, the epithermal neutron shielding material shell, the neutron moderator, the air layer, and the shielding plate in the apparatus for measuring a neutron ambient dose equivalent described above and include all the above-mentioned contents in the apparatus for measuring a neutron ambient dose equivalent, including the dimensions 1 and 2.
  • R1 in the dimension 1 is not the shortest distance from the center of the thermal neutron detector to the outer shell of the second neutron moderator shell, but corresponds to the shortest distance from the center of the thermal neutron detector to the outer shell of the neutron moderator sphere.
  • FIG. 14 shows the response (PE only in FIG. 14) depending on the neutron energy of the conventional energy measuring apparatus including the polyethylene moderator sphere having the thermal neutron detector located on the center thereof and having a diameter of 19 cm and h*(10)normalized shown by a square filled with black which indicates the neutron fluence-ambient dose equivalent conversion coefficient, and shows that the response of the apparatus at 1 MeV matches the neutron fluence-ambient dose equivalent conversion coefficient. It can be seen from FIGS. 1 and 14 that in the case of the conventional measuring apparatus, a difference between the response of the apparatus and the neutron fluence-ambient dose equivalent conversion coefficient in the energy range of 1 MeV or less is 10 times or more.
  • FIG. 15 shows the response (PE + B 4 C in FIG. 15) depending on the neutron energy of the apparatus in which the apparatus in FIG. 14 further includes the boron carbide epithermal neutron shielding material shell, and shows h*(10)normalized shown by a square filled with black which indicates the neutron fluence-ambient dose equivalent conversion coefficient.
  • the epithermal neutron shielding material shell has a hexagonal prism shape having a thickness of 1 cm
  • the thermal neutron detector is located at the center of the hexagonal prism
  • the shortest distance from the center of the thermal neutron detector to the inner shell (inside surface) of the epithermal neutron shielding material shell is 4 cm.
  • FIG. 16 shows the response (PE + B 4 C + Air plate in FIG. 16) depending on the neutron energy of the apparatus in FIG. 15 further including the air layer, and shows the response depending on the neutron energy of the apparatus corresponding to FIGS. 8 and 9.
  • the h*(10)normalized shown by a square filled with black in FIG. 16 indicates the neutron fluence-ambient dose equivalent conversion coefficient.
  • the air layer has the hollow disk shape having a thickness of 0.34 cm (width of the open aperture), the thermal neutron detector was located at the center of the circular hollow, and the shortest distance from the center of the thermal neutron detector to the hollow surface of the disk was 1.4 cm.
  • the response of the apparatus of 5 keV or less is increased by the air layer, and the response curve of the apparatus becomes similar to the neutron fluence-ambient dose equivalent conversion coefficient in the energy range of several keV or less, and it can be seen that the curve shape (change in conversion coefficient depending on the change in energy) of the neutron fluence-ambient dose equivalent conversion coefficient has a response reproduced substantially similarly.
  • the neutron response curve of the apparatus in the region from the thermal neutron to the epithermal neutron has a shape similar to the neutron fluence-ambient dose equivalent conversion coefficient curve, but the response is larger than the neutron fluence-ambient dose equivalent conversion coefficient curve.
  • FIG. 17 shows the response (PE + B 4 C + Air plate + B 4 C addition in FIG. 17) depending on the neutron energy of the apparatus in which the apparatus in FIG. 16 further includes the boron carbide shielding plate, and shows the response depending on the neutron energy of the apparatus corresponding to FIG. 12.
  • the h*(10)normalized shown by a square filled with black in FIG. 17 indicates the neutron fluence-ambient dose equivalent conversion coefficient.
  • the hollow hexagonal plate having the hexagonal hollow is inserted so as to be in contact with the epithermal neutron shielding film on the upper and lower sides of the through region through which the air layer penetrates, the thickness of the hollow hexagonal plate (the first and second shield plates, respectively) was 0.33 cm, and the width of the plate was 2 cm.
  • the response of the apparatus substantially matches the neutron fluence-ambient dose conversion coefficient in a wide energy range from 0.025 eV to 20 MeV.
  • the present invention includes a method for measuring a thermal neutron ambient dose equivalent using the apparatus for measuring a neutron ambient dose equivalent described above.

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Abstract

An apparatus for measuring a neutron ambient dose equivalent includes: a thermal neutron detector; a first neutron moderator shell which encloses the thermal neutron detector; an epithermal neutron shielding material shell which encloses the first neutron moderator shell; a second neutron moderator shell which encloses an epithermal neutron shielding material shell; and an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the epithermal neutron shielding material shell.

Description

APPARATUS FOR MEASURING NEUTRON AMBIENT DOSE EQUIVALENT AND METHOD FOR MEASURING NEUTRON AMBIENT DOSE EQUIVALENT USING THEREOF
The present invention relates to an apparatus and method for measuring a neutron ambient dose equivalent, and more particularly, to an apparatus for measuring a neutron ambient dose equivalent which matches response of the apparatus for measuring a neutron ambient dose equivalent with a neutron fluence-ambient dose equivalent conversion coefficient curve in a wide energy range from a thermal neutron to a fast neutron and a method for measuring a neutron ambient dose equivalent using the same.
A neutron ambient dose equivalent has about 100 times difference depending on neutron energy, and thus, in principle, only when a value of the neutron energy is known, it is possible to accurately calculate the neutron ambient dose equivalent. A change in the neutron ambient dose equivalent depending on the neutron energy is given by the neutron fluence-ambient dose equivalent conversion coefficient (thick black solid line in FIG. 1), and if the neutron fluence indicating the number of neutrons per unit area depending on the neutron energy is known, it is possible to obtain the neutron ambient dose equivalent by multiplying the neutron fluence by the neutron fluence-ambient dose equivalent conversion coefficient.
A neutron ambient dose equivalent meter usually is a neutron measuring instrument which measures a neutron ambient dose equivalent rate for a thermal neutron to a degree at which neutron kinetic energy is about 0.025eV which constitute a Maxwell-Boltzmann distribution to a fast neutron up to about 20 MeV.
The neutron ambient dose equivalent meter usually has a shape in which a thermal neutron detector is inserted into a spherical moderator having a diameter of about 20 cm to 25 cm or a cylindrical moderator having a diameter and a height of about 20 cm to 25 cm. 6Li, 10B, and He 3 react well with neutrons and are widely used in the neutron detector. Response(response of 6Li, 10B, and He 3) is inversely proportional to a neutron speed. Therefore, since the thermal neutron response is largest, as proposed in Korean Patent No. 10-1281083, an apparatus including a polyethylene Bonner sphere of various sizes and a thermal neutron detector is widely used as a neutron measuring instrument.
According to a basic measurement principle of measuring the neutron ambient dose equivalent rate using the neutron ambient dose equivalent meter, neutrons incident on the neutron ambient dose equivalent meter are decelerated to the thermal neutrons in the moderator, and a count rate is measured by the thermal neutron detector inserted thereinto. Since the neutron ambient dose equivalent meter cannot measure the incident neutron energy, the measured count rate is calibrated at the reference neutron ambient dose equivalent rate to obtain a ratio of the count rate and the neutron ambient dose equivalent rate, and the obtained ratio is applied and thus indicated by the neutron ambient dose equivalent rate.
FIG. 1 shows the response of neutron ambient dose equivalent meters (LB6411 I, leake remmeter, Eberline NRD, Studsvik2202D in FIG. 1) which is already developed and neutron fluence-ambient dose equivalent conversion coefficient curve (thick black solid line in FIG. 1). Referring to a response curve, most of the neutron ambient dose equivalent meters are generally matched well in a 1 MeV range, but largely have 10 times or more difference in an epithermal neutron range and a thermal neutron range having a neutron energy range from 1 eV to 10 keV. Therefore, in the already developed neutron ambient dose equivalent meter, a measured value of the neutron ambient dose equivalent meter differs from an actual neutron ambient dose equivalent rate depending on a neutron energy distribution of a neutron field to be measured.
There are two matters which need to be considered when designing a good-performance neutron ambient dose equivalent meter. First, the neutron energy to be usually measured is in a very large energy range, so neutron dosimeters need to be operated at meV to several tens of MeV to be able to accurately measure the neutron ambient dose equivalent rate. Second, according to the ideal neutron ambient dose equivalent meter, the response depending on the neutron energy needs to be the same as the neutron fluence-ambient dose equivalent conversion coefficient.
However, as shown in FIG. 1, the shape of the neutron energy spectrum greatly differs depending on the neutron field, and therefore development of a neutron ambient dose equivalent meter using a representative neutron spectrum has a long way to go. In addition, as shown by a thick black solid line in FIG. 1, the neutron fluence-ambient dose equivalent conversion coefficient has a sharp change depending on the neutron energy in the energy range from 10 keV to 1 MeV, but it is difficult to develop the neutron ambient dose equivalent meter having the same sharp change in response, and therefore a neutron ambient dose equivalent meter having satisfactory performance has not yet been developed.
In addition, the neutron ambient dose equivalent meter basically has a structure in which neutrons are decelerated and converted into thermal neutrons and then measured by the thermal neutron detector inserted into the center thereof. Since a polyethylene having a diameter of 20 cm or more is usually used in order to decelerate neutrons having a neutron energy of 1 MeV or more, the neutron ambient dose equivalent meter is heavy as a mass of about 9 kg.
An object of the present invention is to provide an apparatus for measuring a neutron ambient dose equivalent which matches response depending on neutron energy in a wide energy range from a thermal neutron to a fast neutron with a neutron fluence-ambient dose equivalent conversion coefficient curve and a method for measuring a neutron ambient dose equivalent using the same.
In one general aspect, an apparatus for measuring a neutron ambient dose equivalent includes: a thermal neutron detector; a first neutron moderator shell which encloses the thermal neutron detector; an epithermal neutron shielding material shell which encloses the first neutron moderator shell; a second neutron moderator shell which encloses the epithermal neutron shielding material shell; and an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the epithermal neutron shielding material shell .
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the air layer may penetrate through the epithermal neutron shielding material shell, and may have one end located inside the first neutron moderator shell.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the second neutron moderator shell may have a spherical, polyhedral, cylindrical, or polygonal prism shape.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the air layer may have a hollow disk shape or a hollow polygonal plate shape.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the open aperture formed on the surface of the second neutron moderator shell by the air layer may form a closed curve or a closed curved line.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the epithermal neutron shielding material shell may have a shape of a sphere, a polyhedron, a cylinder, or a polyprism.
The apparatus for measuring a neutron ambient dose equivalent according to an embodiment of the present invention may further include a shielding plate which contacts the epithermal neutron shielding material shell along an outer circumference of the epithermal neutron shielding material shell, covers at least a part of the air layer, and shields an epithermal neutron introduced into the air layer through the second neutron moderator shell.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the epithermal neutron shielding plate may include a first shielding plate and a second shielding plate facing each other with the air layer interposed therebetween.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the first neutron moderator shell and the second neutron moderator shell may be formed of polyethylene, and the epithermal neutron shielding material shell may be formed of boron carbide.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the apparatus for measuring a neutron ambient dose equivalent may satisfy the following dimension 1.
[Dimension 1]
R2 = 0.25R1 to 0.8R1
R3 = 0.05R2 to 0.6R2
T1 = 0.05R1 to 0.3R1
D1 = 0.01R1 to 0.05R1
In the dimension 1, R1 is a shortest distance from the center of the thermal neutron detector to a outer shell(outer surface, outer circumference) of the second neutron moderator shell, R2 is a shortest distance from the center of the thermal neutron detector to a inner shell(inner surface, inner circumference) of the epithermal neutron shielding material shell, R3 is a shortest distance from the center of the thermal neutron detector to one end of the air layer located at the inside of the epithermal neutron shielding material shell, T1 is a thickness of the second neutron moderator shell, and D1 is a width of the open aperture.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the thickness and the width of the shielding plate may satisfy the following dimension 2.
[Dimension 2]
T2 = 0.02R1 to 0.2R1
W1 = 0.2R4 to 0.8R4
In the dimension 2, T2 is a thickness of the shielding plate, W1 is a width of the shielding plate, R1 is a shortest distance from the center of the thermal neutron detector to an outer shell of the second neutron moderator shell, and R4 is a shortest distance from the open aperture of the second neutron moderator shell to an outer shell of the epithermal neutron shielding material shell.
In another general aspect, an apparatus for measuring a neutron ambient dose equivalent includes: a neutron moderator sphere in which a thermal neutron detector is located; an epithermal neutron shielding material shell which is located inside the neutron moderator sphere to enclose a detector with being spaced apart from the thermal neutron detector; a hollow disk-shaped air layer which forms an open aperture along a circumference of the neutron moderator sphere, penetrates through the epithermal neutron shielding material shell, and has a thermal neutron detector located at a center of the hollow; and a shielding plate which contacts the epithermal neutron shielding material shell along an outer circumference of the epithermal neutron shielding material shell and covers at least a part of an air layer to shield an epithermal neutron introduced into the air layer through the second neutron moderator shell.
In still another general aspect, a method for measuring a neutron ambient dose equivalent using the apparatus for measuring a neutron ambient dose equivalent described above is provided.
The apparatus for measuring a neutron ambient dose equivalent according to the present invention has an advantage in that the neutron response of the apparatus substantially matches the neutron fluence-ambient dose equivalent conversion coefficient in a wide energy range from 0.025 eV to 20 MeV.
It is advantageous that the apparatus for measuring a neutron ambient dose equivalent according to the present invention is lightweight and has good mobility as it can measure the neutron energy in a wide energy range from 0.025 eV to 20 MeV based on a single neutron moderator sphere.
The apparatus for measuring a neutron ambient dose equivalent according to the present invention can monitor the neutron ambient dose equivalent in real time.
FIG. 1 is a diagram showing a response and neutron fluence-ambient dose equivalent conversion coefficient of the conventional apparatus for measuring a neutron ambient dose equivalent.
FIG. 2 is a perspective view of an apparatus for measuring a neutron ambient dose equivalent according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view taken along line A-A in the perspective view of FIG. 2.
FIG. 4 is another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
FIG. 5 is a cross-sectional view taken along line A-A in the perspective view of FIG. 4.
FIG. 6 is still another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
FIG. 7 is still another perspective view of an apparatus for measuring a neutron ambient dose equivalent according to an embodiment of the present invention.
FIG. 8 is still another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
FIG. 9 is a cross-sectional view taken along line A-A in the perspective view of FIG. 8.
FIG. 10 is another cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
FIG. 11 is a view showing only a shielding plate in FIG. 10.
FIG. 12 is still another cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
FIG. 13 is a view separately showing only the shielding plate in FIG. 12.
FIG. 14 is a diagram showing the response and neutron fluence-ambient dose equivalent conversion coefficient of the conventional apparatus for measuring a neutron ambient dose equivalent including a polyethylene moderator sphere in which a thermal neutron detector is located at a center of the sphere.
FIG. 15 is a diagram showing the response and the neutron fluence-ambient dose equivalent conversion coefficient curve depending on the neutron energy of the apparatus including the polyethylene moderator sphere where the thermal neutron detector is located at the center of the sphere and a boron carbide epithermal neutron shielding material shell embedded in the polyethylene moderator sphere so that the thermal neutron detector is located at a center therein.
FIG. 16 is a diagram showing the response and the neutron fluence-ambient dose equivalent conversion coefficient curve depending on the neutron energy of the apparatus including the polyethylene moderator sphere where the thermal neutron detector is located at the center of the sphere, the boron carbide epithermal neutron shielding material shell embedded in the polyethylene moderator sphere so that the thermal neutron detector is located at a center therein, and an air layer which forms an open aperture in the moderator sphere and penetrates through the epithermal neutron shielding material shell.
FIG. 17 is a diagram showing the response and the neutron fluence-ambient dose equivalent conversion coefficient curve depending on the neutron energy of the apparatus including the polyethylene moderator sphere where the thermal neutron detector is located at the center of the sphere, the boron carbide epithermal neutron shielding material shell embedded in the polyethylene moderator sphere so that the thermal neutron detector is located at a center therein, the air layer which forms an open aperture in the moderator sphere and penetrates through the epithermal neutron shielding material shell, and a shielding plate which contacts a circumference of an outer surface of the epithermal neutron shielding material shell and covers the air layer adjacent to the outer surface of the epithermal neutron shielding material shell.
Hereinafter, an apparatus for measuring a neutron ambient dose equivalent according to the present invention will be described in detail with reference to the accompanying drawings. The following introduced drawings are provided by way of example so that the spirit of the present invention can be sufficiently transferred to those skilled in the art to which the present invention pertains. Therefore, the present invention is not limited to the accompanying drawings provided below, but may be embodied in many different forms. In addition, the accompanying drawings suggested below will be exaggerated in order to clear the spirit of the present invention. Technical terms and scientific terms used in the present specification have the general meaning understood by those skilled in the art to which the present invention pertains unless otherwise defined, and a description for the known function and configuration unnecessarily obscuring the gist of the present invention will be omitted in the following description and the accompanying drawings.
An apparatus for measuring a neutron ambient dose equivalent includes: a thermal neutron detector; a first neutron moderator shell which encloses the thermal neutron detector; an epithermal neutron shielding material shell which encloses the first neutron moderator shell; a second neutron moderator shell which encloses the epithermal neutron shielding material shell; and an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the epithermal neutron shielding material shell. In this case, the first neutron moderator shell may be a shell containing a first neutron moderator which converts a neutron into a thermal neutron, the second neutron moderator shell may be a shell containing a second neutron moderator shell which converts a neutron into a thermal neutron, and the epithermal neutron shielding material shell may be a shell containing an epithermal neutron shielding material which absorbs and/or removes an epithermal neutron.
In the apparatus for measuring a neutron ambient dose equivalent according to the present invention, the first neutron moderator shell and the second neutron moderator shell may each serve to reduce a neutron to convert the neutron into the thermal neutron, and the epithermal neutron shielding material shell may serve to remove the epithermal neutron introduced into the thermal neutron detector through the second neutron moderator shell to reduce the response of the measuring apparatus in an energy range from several keV to 1 MeV.
The air layer which forms the open aperture along the circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the neutron shielding material shell may serve to improve the response of the measuring apparatus in the energy range of several keV or less which is excessively reduced by the epithermal neutron shielding material shell provided to shield the epithermal neutron, and may serve as an epithermal neutron moving passage through which the epithermal neutron passes through the second neutron moderator shell and an epithermal neutron shielding material shell range and is directly introduced into the first neutron moderator shell contacting the detector.
Specifically, the air layer may be a hollow disk or a hollow polygonal plate depending on the shape of the second neutron moderator shell, and the thermal neutron detector enclosed by the neutron moderator derived from the first neutron moderator shell may be located at the center of the hollow.
As described above, the apparatus for measuring a neutron ambient dose equivalent according to the present invention has a basic detection structure for detecting a thermal neutron by converting the neutron into the thermal neutron by the neutron moderator. However, as shown in FIG. 1 and well known to those skilled in the neutron measurement related technology, when the neutron energy is measured by converting a neutron into a thermal neutron using a neutron moderator, the response well matches the neutron fluence-ambient dose equivalent conversion coefficient curve near the 1 MeV, but the excessively high response appears in the energy range lower than 1 MeV.
The apparatus for measuring a neutron ambient dose equivalent according to the present invention converts a neutron into a thermal neutron by the neutron moderator and measures the thermal neutron, and may have very similar response to the neutron fluence-ambient dose equivalent conversion coefficient curve in a wide energy range from a thermal neutron to a fast neutron by lowering an excessively high response against the neutron fluence-ambient dose equivalent conversion coefficient curve in the epithermal neutron-thermal neutron energy range by the epithermal neutron shielding material interposed between the neutron moderators and improving, by using the air layer, the response in the thermal neutron (and near) energy range excessively lowered by the epithermal neutron shielding material.
In detail, as a result of the present applicant designing and testing a measuring apparatus having various structures to improve the response which is excessively lowered in an energy range of several keV or less by the epithermal neutron shielding material shell, the present applicant found that the response in the energy range of several keV or less is not improved as much as desired even when a size, a shape, and an arrangement of channels are different only by pore channels (pore channels formed in the direction of the detector from the surface of the outermost shell with opened pore channels) such as a bar or a cylinder and found that the response in the energy range of several keV or less is insignificant but the epithermal neutron shielding material shell is inactivated by a plurality of channels spaced apart from each other and the response in the energy range from several keV to 1 MeV is excessively increased.
However, as proposed, when an open aperture is formed along the circumference of the second neutron moderator shell, that is, an opened structure is formed on the surface of the second neutron moderator shell to enclose the circumference of the second neutron moderator shell and the opened structure is formed in a layer form so that the opened structure on the surface of the second neutron moderator shell penetrates through the epithermal neutron shielding material shell and extends to the inside of the first neutron moderator shell, it is possible to improve the response until the response in the energy range of several keV or less substantially matches the neutron fluence-ambient dose equivalent conversion coefficient curve.
As described above, the apparatus for measuring a neutron ambient dose equivalent includes: a thermal neutron detector; a first neutron moderator shell which encloses the thermal neutron detector; an epithermal neutron shielding material shell which encloses the first neutron moderator shell; a second neutron moderator shell which encloses the epithermal neutron shielding material shell; and an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the first neutron moderator shell (in the first neutron moderator shell).
The shape (outer shape) of the second neutron moderator shell determines the overall shape of the apparatus for measuring a neutron ambient dose equivalent. The second neutron moderator shell may have a shape of a sphere, a polyhedron, a cylinder, or a polyprism(polygonal column). Examples of the polyhedron may include a regular hexahedron, a regular octahedron, a cut regular octahedron, a regular dodecahedron, a cut regular dodecahedron, a regular tetradodehedron, a cut regular tetradodehedron, a regular icosahedron, a cut regular icosahedron, and the like, and examples of the polyprism may include a quadrangular (regular tetragonal to rectangular) prism, a pentagonal prism, a hexagonal prism, an octagonal prism, a decagonal prism, a dodecagonal prism and the like. From the viewpoint of uniformly detecting a neutron in all directions, the second neutron moderator shell may have a sphere, a polyhedron having a regular dodecahedron or more, a cylinder, or a polyprism of a pentagonal prism(pentagonal column) or more, but the shape of the second neutron moderator shell is not limited thereto.
Forming the open aperture along the circumference of the second neutron moderator shell may mean that the open aperture forms a closed line (closed band when considering the width of the open aperture) along the circumference of the second neutron moderator shell. The shape of the closed line may correspond to a cross-sectional shape of the second neutron moderator shell. As a specific example, depending on the shape of the second neutron moderator shell, the shape of the closed line may be a closed curve or a closed curved line. As a more specific example, if the second neutron moderator shell is spherical or cylindrical, the open aperture may be a shape of the closed curve, and if the second neutron moderator shell is a shape of a polyhedron or a polyprism, the open aperture may be a shape of a closed curved line.
The shape (outer shape) of the epithermal neutron shielding shell may be a shape in which the epithermal neutron shielding shell may enclose the detector with being spaced apart from the detector by the first neutron moderator shell. As the specific example, the shape of the epithermal neutron shielding material shell may have a shape of the sphere, a polyhedron, a cylinder, or a polyprism, separately of the second neutron moderator shell. The polyhedron may include a regular hexahedron, a regular octahedron, a cut regular octahedron, a regular dodecahedron, a cut regular dodecahedron, a regular tetradodehedron, a cut regular tetradodehedron, a regular icosahedron, a cut icosahedron, and the like, and a polyprism may include a quadrangular (regular tetragonal to rectangular) prism, a pentagonal prism, a hexagonal prism, an octagonal prism, a decagonal prism, a dodecagonal prism and the like. As a substantial example, the second neutron moderator shell may have a sphere, a polyhedron having a regular dodecahedron or more, a cylinder, or a polyprism of a pentagonal prism or more, but the shape of the second neutron moderator shell is not limited thereto. In this case, the epithermal neutron shielding material shell may have a predetermined thickness (uniform thickness).
It goes without saying that the shape of the epithermal neutron shielding material shell and the above-mentioned shell including the epithermal neutron shielding material shell are based on the outer shape of the shell. By setting a direction from the detector toward the surface of the second neutron moderator shell as an outer direction, the outer shape of the other shell (shell B) which is located in the outer direction of one shell and encloses one shell (shell A) may have various shapes such as the shapes of the sphere, the polyhedron, the cylinder, or the polyprism as described above, but it goes without saying that an inner shape of the other shell (shell B) has a shape corresponding to the outer shape of one shell (shell A) to adhere to the one shell without forming an unintended gap, so the other shell (shell B) can enclose the one shell (shell A).
The first neutron moderator shell may be a form that can fill the space between the epithermal shielding material shell and the detector. Specifically, the shape (outer shape) of the first neutron moderator shell may correspond to the inner shape of the epithermal shielding material shell, and may have a shape corresponding to the outer shape of the epithermal neutron shielding material shell as the thickness of the shielding material shell is constant. In one example, the first neutron moderator shell may have the sphere, the polyhedron, the cylinder, or the polyprism, and may have a shape corresponding to the outer shape (or inner shape) of the epithermal neutron shielding material shell. As a more specific example, when the shape of the epithermal neutron shielding material shell is a spherical shape, the first neutron moderator shell may be a sphere in which the detector is located. As another specific example, when the shape of the epithermal neutron shielding material shell is a cylinder, the first neutron moderator shell may have the shape of the cylinder in which the detector is located. As still another specific example, when the shape of the epithermal neutron shielding material shell is a cylinder, the first neutron moderator shell may have the shape of the octagonal prism in which the detector is located.
The thermal neutron detector may be located at the center of the first neutron moderator shell, but the location of the thermal neutron detector is not limited thereto. As the thermal neutron detector, any detector known to be used to detect thermal neutrons in the field of measuring the neutron ambient dose equivalent can be used. As a specific example, the thermal neutron detector may be a BF 3 neutron proportional counter, a He 3 neutron proportional counter or the like, but is not limited thereto, and an active thermal neutron detector capable of transmitting a thermal neutron measurement signal in real time may be used. In addition, the thermal neutron detector may have a spherical to cylindrical shape, but it goes without saying that the present invention can not be limited to the specific form of the thermal neutron detector.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the second neutron moderator shell, the epithermal neutron shielding material shell, the first neutron moderator shell, and the closed line (a closed band when considering the thickness of the air layer) which is an aperture portion formed on the second neutron moderator shell by the air layer may have a concentric structure, and the thermal neutron detector may be located at a center thereof, but they are not necessarily limited to this structure.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the measuring apparatus can include a single thermal neutron detector, which refers to that the measuring apparatus according to the present invention which is the single thermal neutron detector can confirm that the response of the apparatus matches the neutron fluence-ambient dose equivalent conversion coefficient curve in a wide range from 0.025 eV to 20 MeV. Therefore, the detector of the present invention can be constituted as the single thermal neutron detector due to the superiority of the present invention, but it should not be interpreted as excluding the case where two or more thermal neutron detectors are provided.
In addition, the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention may further include a predetermined signal line for transmitting a measured signal output from the thermal neutron detector to the outside of the apparatus, and it goes without saying that the first neutron moderator shell, the epithermal neutron shielding material shell, and the second neutron moderator shell may be provided with a drawing-out hole for drawing-out a signal line 101 of the thermal neutron detector to the outside of the apparatus.
In addition, the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention may further include a calculation unit which receives the measured signal output from the thermal neutron detector through the signal line and calculates the neutron energy based on the number of neutrons (thermal neutrons) counted by the thermal neutron detector and an output unit which outputs (including a display) the neutron energy calculated by the calculation unit.
FIG. 2 is a perspective view of an apparatus for measuring a neutron ambient dose equivalent according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view taken along line A-A in the perspective view of FIG. 2.
FIGS. 2 and 3 show examples in which a second neutron moderator shell 400, an epithermal neutron shielding material shell 300, and a first neutron moderator shell 200 all have a spherical shape, a thermal neutron detector 100 is located at the center of the sphere of the first neutron moderator shell 200 which has a spherical shape, and a hollow disk-shaped air layer 500 is formed.
As in the examples in FIGS. 2 and 3, the air layer 500 forms a ring-shaped open aperture 501 along the circumference of the second neutron moderator shell 400, extends from the open aperture 501, penetrates through the epithermal neutron shielding material shell 300, and extends so that one end 502 is located inside the first neutron moderator shell 200 (inside the first neutron moderator), such that the air layer 500 may have a hollow disk shape.
In the hollow disk-shaped air layer 500, an outer surface of a plate forms the open aperture 501 on the second neutron moderator shell 400 and an inner surface (hollow surface) of the plate may enclose the thermal neutron detector 100 with being spaced apart from the thermal neutron detector 100. FIGS. 2 and 3 show the examples in which a hollow of the hollow disk-shaped air layer 500 has a circular shape, but the shape of hollow in the hollow disk-shaped air layer is not necessarily limited thereto. The hollow in the hollow plate-shaped air layer may have any shape such as a square, a pentagon, a hexagon, and an octagon as long as the air layer can enclose the thermal neutron detector 100 with being spaced apart from the thermal neutron detector 100.
FIG. 4 is another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, and FIG. 5 is a cross-sectional view taken along line A-A in the perspective view of FIG. 4.
FIGS. 4 and 5 show examples in which each of the second neutron moderator shell 400, the epithermal neutron shielding material shell 300, and the first neutron moderator shell 200 is a hexagonal prism shape and a hollow hexagonal plate-shaped air layer 500 is formed. In addition, FIGS. 4 and 5 show examples in which the thermal neutron detector 100, the first neutron moderator shell 200, the epithermal neutron shielding material shell 300, and the hollow hexagonal plate-shaped air layer 500 all have a concentric structure with respect to a longitudinal center line of the hexagonal prism (second neutron moderator shell).
FIG. 6 is another perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention.
The example of FIG. 6 is an example in which the second neutron moderator shell 400, the epithermal neutron shielding material shell 300, and the first neutron moderator shell 200 all have an octagonal prism shape, and the thermal neutron detector 100, the first neutron moderator shell 200, and the epithermal neutron shielding material shell 300 all have a concentric structure with respect to a longitudinal center line of the octagonal prism which is the second neutron moderator shell 400. As the air layer 500 forms the open aperture 501 of the closed line along the circumference of the second neutron moderator shell 400, the shape of the air layer may be changed depending on the shape of the second neutron moderator shell. In the example of FIG. 6, the air layer 500 may have the hollow octagonal plate shape as the second neutron moderator shell 400 has an octagonal prism shape. In this case, although FIG. 6 shows an example in which the hollow of the octagonal plate is a circle, as described above, the shape of the hollow may be a polygonal shape including a circle, a square, a pentagon, a hexagon, an octagon, and the like, independent of the shape of the plate.
FIG. 7 is a perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention. FIG. 7 shows an example in which the second neutron moderator shell 400 has a cylindrical shape, the epithermal neutron shielding material shell 300 has a hexagonal prism shape, and the first neutron moderator shell 200 has a hexagonal prism shape, and as shown in FIG. 2, the hollow disk-shaped air layer 500 is formed. FIG. 7 shows an example in which the thermal neutron detector 100, the first neutron moderator shell 200, and the epithermal shielding material shell 300 have a concentric structure with respect to the longitudinal center line of the cylinder (second neutron moderator shell).
FIG. 8 is a perspective view of the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, and FIG. 9 is a cross-sectional view taken along line A-A in the perspective view of FIG. 8. FIGS. 8 and 9 show examples in which the second neutron moderator shell 400 has a spherical shape, the epithermal neutron shielding material shell 300 has a hexagonal prism shape, and the first neutron moderator shell 200 has a hexagonal prism shape, shows an example in which the thermal neutron detector 100, the first neutron moderator shell 200, and the epithermal neutron shielding material shell 300 all have a concentric structure with respect to a center line N-S of the sphere connecting between a top point N and a bottom point S of the sphere, and shows an example in which the hollow disk-shaped air layer 500 is formed.
As in the examples shown in FIGS. 2 to 9, the air layer 500 may have the hollow disk shape or the hollow polygonal plate shape depending on the shape of the second neutron moderator shell, and the shape of the hollow may be a polygonal shape including a circle, a square, a pentagon, a hexagon, an octagon, and the like, independent of the shape of the plate. Describing the air layer in terms of the hollow disk or the hollow polygonal plate shape, a "one end" which penetrates through the epithermal shielding material shell and is located inside (in) the first neutron moderator shell means that the hollow disk or the hollow polygonal plate is located inside (in) the first neutron moderator shell, and one end of the air layer may mean a hollow surface of the hollow.
The apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention may further include a shielding plate which contacts the epithermal neutron shielding material shell along the outer circumference of the epithermal neutron shielding material shell together with the thermal neutron detector, the first neutron moderator shell, the epithermal neutron shielding material shell, and the second neutron moderator shell, and the air layer, and covers at least a part of the air layer to shield the epithermal neutron introduced into the air layer through the second neutron moderator shell. In this case, covering the air layer with the shielding plate means that the shielding plate is located between the air layer and the second neutron moderator shell.
As described above, the air layer can serve as a moving (introduction) passage for the thermal neutron into which the thermal neutron can be directly introduced into the first neutron moderator shell, such that the response of the measuring apparatus in the energy range of several keV or less can be improved.
However, there is a risk that the epithermal neutron moving in the second neutron moderator shell is also introduced into the air layer as the air layer has a structure to penetrate through the epithermal neutron shielding material shell. As a result, there is a risk that the response in the energy range from several keV to 1 MeV is increased undesirably.
The shielding plate may serve to fundamentally prevent the epithermal neutron from being introduced from the second neutron moderator shell into the air layer. It is possible to stably maintain the response in the energy range from several keV to 1 MeV which is lowered by the epithermal neutron shielding material shell simultaneously with improving the response in the energy range of several keV or less by the air layer due to the shielding of the epithermal neutron of the shielding plate.
As the air layer may have the hollow disk or the hollow polygonal plate shape, it is more preferable that the shielding plate includes a first shielding plate which can shield the epithermal neutron introduced from an upper part thereof into the air layer through the second neutron moderator shell and a second shielding plate which can shield the epithermal neutron from a lower part thereof into the air layer through the second neutron moderator shell.
That is, the shielding plate may include the first shielding plate and the second shielding plate facing each other with the air layer interposed therebetween, and each of the first shielding plate and the second shielding plate may contact the epithermal neutron shielding material shell along the outer circumference of the epithermal neutron shielding material shell and cover at least a part of the air layer.
FIG. 10 is a cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent shown in FIG. 2 which further includes shield plates 610 and 620, and FIG. 11 is a perspective view separately showing only the first shielding plate 610 and the second shielding plate 620 facing each other with being spaced apart from each other by a width of an open aperture (D1: thickness of the air layer) by the air layer 500 in FIG. 10. FIG. 12 is a cross-sectional view of the apparatus for measuring a neutron ambient dose equivalent shown in FIG. 8 which further includes shield plates 610 and 620, and FIG. 13 is a perspective view separately showing only the first shielding plate 610 and the second shielding plate 620 facing each other with being spaced apart from each other by a width (D1: thickness of the air layer) of an open aperture by the air layer 500 in FIG. 12.
As in examples shown in FIGS. 10 to 13, the shielding plate may include the first shielding plate 610 and the second shielding plate 620 which cover the air layer 500 provided on upper and lower parts thereof, respectively. The first shielding plate 610 and the second shielding plate 620 are spaced apart from each other by the air layer interposed therebetween, and both the first shielding plate 610 and the second shielding plate 620 may contact the epithermal neutron shielding material shell 300 near a through region through which the air layer penetrates and enclose the epithermal neutron shielding material shell 300.
As described above, the shielding plate contacts the epithermal neutron shielding material shell 300 to enclose the epithermal neutron shielding material shell 300 and covers at least a part of the air layer 500, such that the shielding plate may have a hollow plate shape. The shape of the hollow shielding plate may be a hollow disk shape or a hollow polygonal plate shape, and examples of the hollow polygonal plate may include a square, a pentagon, a hexagon, an octagon, and the like. As the shielding plate has a structure to contact the epithermal neutron shielding material shell and to enclose the epithermal neutron shielding material shell, the size and shape of the hollow in the shielding plate having the hollow disk or the hollow polygonal plate shape may correspond to the size and shape of the epithermal neutron shielding material shell (see FIGS. 11 and 13). In addition, it goes without saying that how much the air layer is covered with the shielding plate can be controlled by the width of the hollow shielding plate.
As the example of FIG. 10 is the example in which the epithermal neutron shielding material shell 300 has a spherical shape, the first shielding plate 610 and the second shielding plate 620 may each be the hollow disk shape having the circular hollow. As the example of FIG. 12 is the example in which the epithermal neutron shielding material shell 300 is an octagonal prism shape, the first shielding plate 610 and the second shielding plate 620 may each have the hollow octagonal plate shape having an octagonal hollow. That is, the size and shape of the hollow shielding plate may correspond to the size and shape of the cross section of the epithermal neutron shielding material shell based on the surface penetrated by the air layer.
In addition, FIGS. 10 and 12 show examples in which the width of the shielding plate is smaller than the shortest distance from the open aperture located on the surface (outer surface) or the surface of the second neutron moderator shell 400 to the surface (outer surface) of the epithermal neutron shielding material shell to cover a part of the air layer located between the epithermal neutron shielding material shell and the second neutron moderator shell, but the present invention is not limited thereto, and it goes without saying that the shielding plate may completely cover the air layer located between the epithermal neutron shielding material shell and the second neutron moderator shell.
In addition, FIGS. 10 and 12 show the examples in which the first shielding plate and the second shielding plate have the same size and shape as each other, but the present invention is not limited thereto, and it goes without saying that the first shielding plate which is the hollow disk and the second shielding plate which is the hollow polygonal plate or the first shielding plate and the second shielding plate which have different widths and are the hollow disk, and the like may have different shapes and sizes if necessary.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, as a material of the first neutron moderator of the first neutron moderator shell and the second neutron moderator of the second neutron moderator shell, any material known to convert a neutron into a thermal neutron may be used, and in detail, a representative example may be polyethylene, but the present invention is not limited to the specific neutron moderator material.
In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, as the epithermal shielding material of the epithermal neutron shielding material shell, any material known to absorb and remove the epithermal neutron may be used, and the specific and representative example may be boron carbide (B 4C), but the present invention is not limited to the specific epithermal neutron shielding material.
In the case of the conventional measuring apparatus which converts a neutron into the thermal neutron using the neutron moderator and measures the thermal neutron with a thermal neutron detector, it is known that the response of the apparatus matches the neutron fluence-ambient dose equivalent conversion coefficient curve in the vicinity of 1 MeV, but as the example shown in FIG. 1, the conventional measuring apparatus has the excessively large response against the neutron fluence-ambient dose equivalent conversion coefficient in an energy range of 1 MeV or less. In the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention, the response in the range from several keV to 1 MeV may substantially match the neutron fluence-ambient dose equivalent conversion coefficient by the epithermal neutron shielding material shell, and the response in the range of several keV or less which is excessively lowered by the epithermal neutron shielding material shell may be improved by the air layer to make the response of the apparatus substantially match the neuron fluence-ambient dose equivalent conversion coefficient even in the range of several keV or less. In addition, the response in the range from several keV to 1 MeV may be kept stable to substantially match the neutron fluence-ambient dose equivalent conversion coefficient, by the shielding plate that prevents the thermal neutron from being introduced into the air layer even when the air layer is provided.
Accordingly, in consideration of the type of neutrons to be measured, the type of neutron generation sources, the detailed form of the neutron fluence-ambient dose equivalent conversion coefficient curve and the like, the size of the second neutron moderator shell, the size of the first neutron moderator shell, the thickness of the epithermal neutron shielding material shell, the thickness of the air layer (= width of the open aperture), the detailed location of one end of the air layer located in the first neutron moderator shell, the width of the shielding plate (width of the range of the air layer covered with the shielding plate), the thickness of the shielding plate and the like can be appropriately changed in design.
However, as an example of the detailed dimension in which the response of the apparatus substantially matches the neutron fluence-ambient dose equivalent factor curve in the overall range from 0.025 eV to 20 MeV, the apparatus for measuring a neutron ambient dose equivalent according to the embodiment of the present invention may satisfy the following dimension 1 and preferably satisfy the following dimension 1 and dimension 2.
[Dimension]
R2= 0.25R1 to 0.8R1, specifically 0.3R1 to 0.6R1
R3= 0.05R2 to 0.6R2, specifically 0.15R2 to 0.5R2
T1= 0.05R1 to 0.3R1, specifically 0.05R1 to 0.2R1
D1= 0.01R1 to 0.05R1, specifically 0.02R1 to 0.05R1
In the dimension 1, R1 is the shortest distance from the center of the thermal neutron detector to the outer shell of the second neutron moderator shell, R2 is a shortest distance from the center of the thermal neutron detector to a inner shell(inner surface, inner circumference) of the epithermal neutron shielding material shell, R3 is the shortest distance from the center of the thermal neutron detector to one end of the air layer located on the inside (in the first neutron moderator shell) of the neutron shielding material shell, T1 is the thickness of the second neutron moderator shell, and D1 is the width of the open aperture (thickness of the air layer).
[Dimension 2]
T2= 0.02R1 to 0.2R1, specifically 0.02R1 to 0.1R1
W1= 0.2R4 to 0.8R4, specifically 0.2R4 to 0.6R4
In the dimension 2, T2 is the thickness of the shielding plate, W1 is the width of the shielding plate, R1 is the shortest distance from the center of the thermal neutron detector to the outer shell of the second neutron moderator shell, and R4 is the shortest distance from the open aperture of the second neutron moderator shell to the outer shell of the epithermal neutron shielding material shell.
As a practical example based on the most commonly used size of the Bonner sphere based neutron measuring apparatus, R1 may be 9.5 cm to 12.7 cm, and the present invention is not necessarily limited to the above-mentioned specific values.
An apparatus for measuring a neutron ambient dose equivalent according to another advantageous aspect of the present invention includes: a neutron moderator sphere which has a thermal neutron detector located therein; an epithermal neutron shielding material shell which is located inside the neutron moderator sphere to enclose a detector with being spaced apart from the thermal neutron detector; a hollow disk-shaped air layer which forms an open aperture along a circumference of the neutron moderator sphere, penetrates through the epithermal neutron shielding material shell, and has a thermal neutron detector located at a center of the hollow; and a shielding plate which contacts the epithermal neutron shielding material shell along a circumference of an outer side of the epithermal neutron shielding material shell and covers at least a part of an air layer to shield an epithermal neutron introduced into the air layer through the second neutron moderator shell.
The apparatus for measuring a neutron ambient dose equivalent according to another embodiment of the present invention corresponds to the neutron modulator sphere having the configuration in which the first neutron moderator shell and the second neutron modulator shell are integrated, not the configuration in which the first neutron moderator shell and the second neutron modulator shell are separated from each other in the apparatus for measuring a neutron ambient dose equivalent described above, and corresponds to the case in which the epithermal neutron shielding material shell is inserted into the neutron moderator sphere.
Accordingly, in another aspect of the present invention, the thermal neutron detector, the epithermal neutron shielding material shell, the neutron moderator, the air layer, and the shielding plate are similar to or the same as the thermal neutron detector, the epithermal neutron shielding material shell, the neutron moderator, the air layer, and the shielding plate in the apparatus for measuring a neutron ambient dose equivalent described above and include all the above-mentioned contents in the apparatus for measuring a neutron ambient dose equivalent, including the dimensions 1 and 2. However, in another embodiment of the present invention, it goes without saying that R1 in the dimension 1 is not the shortest distance from the center of the thermal neutron detector to the outer shell of the second neutron moderator shell, but corresponds to the shortest distance from the center of the thermal neutron detector to the outer shell of the neutron moderator sphere.
FIG. 14 shows the response (PE only in FIG. 14) depending on the neutron energy of the conventional energy measuring apparatus including the polyethylene moderator sphere having the thermal neutron detector located on the center thereof and having a diameter of 19 cm and h*(10)normalized shown by a square filled with black which indicates the neutron fluence-ambient dose equivalent conversion coefficient, and shows that the response of the apparatus at 1 MeV matches the neutron fluence-ambient dose equivalent conversion coefficient. It can be seen from FIGS. 1 and 14 that in the case of the conventional measuring apparatus, a difference between the response of the apparatus and the neutron fluence-ambient dose equivalent conversion coefficient in the energy range of 1 MeV or less is 10 times or more.
FIG. 15 shows the response (PE + B 4C in FIG. 15) depending on the neutron energy of the apparatus in which the apparatus in FIG. 14 further includes the boron carbide epithermal neutron shielding material shell, and shows h*(10)normalized shown by a square filled with black which indicates the neutron fluence-ambient dose equivalent conversion coefficient. In detail, the epithermal neutron shielding material shell has a hexagonal prism shape having a thickness of 1 cm, the thermal neutron detector is located at the center of the hexagonal prism, and the shortest distance from the center of the thermal neutron detector to the inner shell (inside surface) of the epithermal neutron shielding material shell is 4 cm.
It can be seen from FIG. 15 that as the epithermal neutron shielding material shell is provided, the response of the apparatus in the range from 5 keV to 1 MeV is close to the neutron fluence-ambient dose equivalent conversion coefficient, but the response of the apparatus of 5 keV or less is remarkably decreased.
FIG. 16 shows the response (PE + B 4C + Air plate in FIG. 16) depending on the neutron energy of the apparatus in FIG. 15 further including the air layer, and shows the response depending on the neutron energy of the apparatus corresponding to FIGS. 8 and 9. In this case, the h*(10)normalized shown by a square filled with black in FIG. 16 indicates the neutron fluence-ambient dose equivalent conversion coefficient. In detail, the air layer has the hollow disk shape having a thickness of 0.34 cm (width of the open aperture), the thermal neutron detector was located at the center of the circular hollow, and the shortest distance from the center of the thermal neutron detector to the hollow surface of the disk was 1.4 cm.
It can be seen from FIG. 16 that the response of the apparatus of 5 keV or less is increased by the air layer, and the response curve of the apparatus becomes similar to the neutron fluence-ambient dose equivalent conversion coefficient in the energy range of several keV or less, and it can be seen that the curve shape (change in conversion coefficient depending on the change in energy) of the neutron fluence-ambient dose equivalent conversion coefficient has a response reproduced substantially similarly. However, it can be seen that the neutron response curve of the apparatus in the region from the thermal neutron to the epithermal neutron has a shape similar to the neutron fluence-ambient dose equivalent conversion coefficient curve, but the response is larger than the neutron fluence-ambient dose equivalent conversion coefficient curve.
FIG. 17 shows the response (PE + B 4C + Air plate + B 4C addition in FIG. 17) depending on the neutron energy of the apparatus in which the apparatus in FIG. 16 further includes the boron carbide shielding plate, and shows the response depending on the neutron energy of the apparatus corresponding to FIG. 12. In this case, the h*(10)normalized shown by a square filled with black in FIG. 17 indicates the neutron fluence-ambient dose equivalent conversion coefficient. In detail, the hollow hexagonal plate having the hexagonal hollow is inserted so as to be in contact with the epithermal neutron shielding film on the upper and lower sides of the through region through which the air layer penetrates, the thickness of the hollow hexagonal plate (the first and second shield plates, respectively) was 0.33 cm, and the width of the plate was 2 cm.
It can be seen from FIG. 17 that when the shielding plate is provided so that the epithermal neutron is not injected into the polyethylene moderator around the thermal neutron detector through the air layer, the response of the apparatus substantially matches the neutron fluence-ambient dose conversion coefficient in a wide energy range from 0.025 eV to 20 MeV.
The present invention includes a method for measuring a thermal neutron ambient dose equivalent using the apparatus for measuring a neutron ambient dose equivalent described above.
Hereinabove, although the present invention has been described by specific matters, embodiments, and drawings, they have been provided only for assisting in the entire understanding of the present invention. Therefore, the present invention is not limited to the embodiments. Various modifications and changes may be made by those skilled in the art to which the present invention pertains from this description.
Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and the following claims as well as all modified equally or equivalently to the claims are intended to fall within the scope and spirit of the invention.

Claims (13)

  1. An apparatus for measuring a neutron ambient dose equivalent, comprising:
    a thermal neutron detector;
    a first neutron moderator shell which encloses the thermal neutron detector;
    an epithermal neutron shielding material shell which encloses the first neutron moderator shell;
    a second neutron moderator shell which encloses the epithermal neutron shielding material shell; and
    an air layer which forms an open aperture along a circumference of the second neutron moderator shell, extends from the open aperture, penetrates through the epithermal neutron shielding material shell, and extends to an inside of the epithermal neutron shielding material shell.
  2. The apparatus of claim 1, wherein the air layer penetrates through the epithermal neutron shielding material shell, and has one end located inside the first neutron moderator shell.
  3. The apparatus of claim 1, wherein the second neutron moderator shell has a spherical, polyhedral, cylindrical, or polyprism shape.
  4. The apparatus of claim 3, wherein the air layer has a hollow disk shape or a hollow polygonal plate shape.
  5. The apparatus of claim 2, wherein the open aperture formed on the surface of the second neutron moderator shell by the air layer forms a closed curve or a closed curved line.
  6. The apparatus of claim 1, wherein the epithermal neutron shielding material shell has a spherical, polyhedral, cylindrical, or polyprism shape.
  7. The apparatus of claim 1, further comprising:
    a shielding plate which contacts the epithermal neutron shielding material shell along an outer circumference of the epithermal neutron shielding material shell, covers at least a part of the air layer, and shields an epithermal neutron introduced into the air layer through the second neutron moderator shell.
  8. The apparatus of claim 7, wherein the shielding plate includes a first shielding plate and a second shielding plate facing each other with the air layer interposed therebetween.
  9. The apparatus of claim 1, wherein the first neutron moderator shell and the second neutron moderator shell are formed of polyethylene, and the epithermal neutron shielding material shell is formed of boron carbide.
  10. The apparatus of claim 1, wherein the apparatus for measuring a neutron ambient dose equivalent satisfies the following dimension 1.
    [Dimension 1]
    R2= 0.25R1 to 0.8R1
    R3= 0.05R2 to 0.6R2
    T1= 0.05R1 to 0.3R1
    D1= 0.01R1 to 0.05R1
    (In the dimension 1, R1 is a shortest distance from the center of the thermal neutron detector to a outer shell of the second neutron moderator shell, R2 is a shortest distance from the center of the thermal neutron detector to a inner shell of the epithermal neutron shielding material shell, R3 is a shortest distance from the center of the thermal neutron detector to one end of the air layer located at the inside of the neutron shielding material shell, T1 is a thickness of the second neutron moderator shell, and D1 is a width of the open aperture).
  11. The apparatus of claim 7, wherein the thickness and the width of the shielding plate satisfy the following dimension 2.
    [Dimension 2]
    T2= 0.02R1 to 0.2R1
    W1= 0.2R4 to 0.8R4
    (in the dimension 2, T2 is a thickness of the shielding plate, W1 is a width of the shielding plate, R1 is a shortest distance from the center of the thermal neutron detector to an outer shell of the second neutron moderator shell, and R4 is a shortest distance from the open aperture of the second neutron moderator shell to an outer shell of the epithermal neutron shielding material shell).
  12. An apparatus for measuring a neutron ambient dose equivalent, comprising:
    a neutron moderator sphere in which a thermal neutron detector is located;
    an epithermal neutron shielding material shell which is located inside the neutron moderator sphere to enclose a detector with being spaced apart from the thermal neutron detector;
    a hollow disk-shaped air layer which forms an open aperture along a circumference of the neutron moderator sphere, penetrates through the epithermal neutron shielding material shell, and has a thermal neutron detector located at a center of the hollow; and
    a shielding plate which contacts the epithermal neutron shielding material shell along an outer circumference of the epithermal neutron shielding material shell and covers at least a part of an air layer to shield an epithermal neutron introduced into the air layer through the second neutron moderator shell.
  13. A method for measuring a neutron ambient dose equivalent using the apparatus for measuring a neutron ambient dose equivalent of any one of claims 1 to 12.
PCT/KR2019/004977 2018-07-23 2019-04-25 Apparatus for measuring neutron ambient dose equivalent and method for measuring neutron ambient dose equivalent using thereof WO2020022615A1 (en)

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JP2001349951A (en) * 2000-06-07 2001-12-21 ▲高▼野 直人 Neutron detector
JP2002311147A (en) * 2001-04-18 2002-10-23 Toshiba Corp Neutron spectrum measuring device and neutron detector
JP2009204581A (en) * 2008-02-29 2009-09-10 Toshiba Corp Neutron measurement device and neutron measurement method
KR20110057807A (en) * 2009-11-25 2011-06-01 한국표준과학연구원 Variable geometry boner sphere system and method for measuring neutron energy spectrum using the same
JP2014142353A (en) * 2007-11-15 2014-08-07 Secretory Of State For Heath Radiation detection

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JP4150831B2 (en) * 2005-06-23 2008-09-17 独立行政法人 日本原子力研究開発機構 Neutron personal dose equivalent measuring instrument
KR101281083B1 (en) 2010-10-19 2013-07-09 한국표준과학연구원 Measurement system and measurement method of neutron energy spectrum using plurality boner sphere and recording medium thereof

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JP2001349951A (en) * 2000-06-07 2001-12-21 ▲高▼野 直人 Neutron detector
JP2002311147A (en) * 2001-04-18 2002-10-23 Toshiba Corp Neutron spectrum measuring device and neutron detector
JP2014142353A (en) * 2007-11-15 2014-08-07 Secretory Of State For Heath Radiation detection
JP2009204581A (en) * 2008-02-29 2009-09-10 Toshiba Corp Neutron measurement device and neutron measurement method
KR20110057807A (en) * 2009-11-25 2011-06-01 한국표준과학연구원 Variable geometry boner sphere system and method for measuring neutron energy spectrum using the same

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