WO2012105694A1 - Scintillateur pour la détection de faisceau de neutrons et dispositif de détection de faisceau de neutrons - Google Patents

Scintillateur pour la détection de faisceau de neutrons et dispositif de détection de faisceau de neutrons Download PDF

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WO2012105694A1
WO2012105694A1 PCT/JP2012/052526 JP2012052526W WO2012105694A1 WO 2012105694 A1 WO2012105694 A1 WO 2012105694A1 JP 2012052526 W JP2012052526 W JP 2012052526W WO 2012105694 A1 WO2012105694 A1 WO 2012105694A1
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scintillator
neutron beam
beam detection
neutron
light
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PCT/JP2012/052526
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English (en)
Japanese (ja)
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範明 河口
澄人 石津
福田　健太郎
敏尚 須山
吉川　彰
健之 柳田
有為 横田
優貴 古谷
藤本　裕
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株式会社トクヤマ
国立大学法人東北大学
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Publication of WO2012105694A1 publication Critical patent/WO2012105694A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T3/00—Measuring neutron radiation
    • G01T3/06—Measuring neutron radiation with scintillation detectors
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/7732—Halogenides
    • C09K11/7733—Halogenides with alkali or alkaline earth metals

Definitions

  • the present invention relates to a neutron beam detection scintillator used for detecting a neutron beam, and more specifically, at least one kind of a fourth periodic element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.
  • the present invention relates to a scintillator for detecting a neutron beam comprising a cordierite-type fluoride single crystal containing a neutron beam and a neutron beam detector using the scintillator.
  • a scintillator is a substance that absorbs radiation and emits fluorescence when irradiated with radiation such as ⁇ rays, ⁇ rays, ⁇ rays, X rays, neutron rays, etc. Used in combination with radiation detection. For this reason, scintillators are applied in many fields such as medical fields such as tomography, industrial fields such as non-destructive inspection, security fields such as belongings inspection, and academic fields such as high energy physics.
  • scintillators there are various types of scintillators depending on the type of radiation and purpose of use.
  • inorganic crystals such as bismuth germanium oxide (Bi 4 Ge 3 O 12 ) and cerium-added gadolinium silicon oxide (Ce: Gd 2 SiO 5 ).
  • an organic crystal such as anthracene, a polymer such as polystyrene and polyvinyltoluene containing an organic phosphor, a liquid scintillator, and a gas scintillator.
  • Neutron beams are thermal neutron beams (about 0.025 eV), epithermal neutron beams (about 1 eV), slow neutron beams (0.03 to 100 eV), medium speed neutron beams (0.1 to 500 keV) depending on energy. And fast neutron rays (500 keV or more).
  • a high-energy neutron beam has a low probability of occurrence of 3 He (n, p) T reaction, that is, low detection sensitivity by a neutron beam detector using 3 He gas. Therefore, the main detection target of the neutron beam detector is a thermal neutron beam with low energy.
  • a method of detecting the fast neutron beam after decelerating it to a thermal neutron beam using a moderator such as polyethylene is used.
  • a moderator such as polyethylene
  • a rem counter or a Bonner sphere spectrometer in which a neutron beam detection unit using 3 He is covered with a spherical polyethylene moderator is used.
  • neutron beam detection apparatuses using 3 He gas that is long and highly sensitive to thermal neutron beams have been used.
  • 3 He gas is rare, in recent years, the price has risen, and replacement with an alternative technology is required.
  • a neutron beam detector using a solid neutron beam scintillator is one of promising candidates as an alternative technology.
  • a substance that emits fluorescence when a neutron beam collides and a molded body made of the substance are referred to as a scintillator for detecting a neutron beam.
  • a scintillator containing lithium 6 ( 6 Li) is one of promising scintillators for detecting solid neutron beams.
  • the scintillator generates ⁇ rays by a nuclear reaction between thermal neutron rays and 6 Li, and then the ⁇ rays emit light by exciting the luminescent center element.
  • Excited luminescence by ⁇ rays has a mechanism different from that of X-rays, ⁇ -rays, and ⁇ -rays.
  • the ratio of ⁇ / ⁇ which is the ratio of the amount of light emitted by ⁇ -ray excitation to the amount of light emitted by X-ray excitation, differs depending on the material of the scintillator The difference arises.
  • a solid neutron beam scintillator is a 6 Li glass scintillator because it has no deliquescence and high-speed response.
  • the scintillator has a problem in that the manufacturing process is complicated and the scintillator cannot be formed into a size larger than a certain degree.
  • the present inventors evaluated several fluoride single crystals by irradiating them with neutron beams in order to attempt application as scintillators for detecting neutron beams.
  • the fluoride crystal containing Li and a divalent or higher valent metal element contains lanthanoid and 1.1 to 20 atoms (atom / nm 3 ) of 6 Li per unit volume, and further has an effective atomic number of 10 to 40.
  • the scintillator for detecting neutron beams has relatively good characteristics (see Patent Document 1).
  • the neutron beam detection scintillator that has been studied in the past has been a scintillator suitable mainly when a photomultiplier tube is used as a photodetector.
  • the scintillator can be used satisfactorily as a scintillator mounted on a photon counting neutron detector using a photomultiplier tube, but a silicon photodiode which is a photodetector suitably used for a survey meter and the like.
  • the use in combination has not been studied.
  • a silicon photodiode has a high sensitivity to light having a long wavelength (approximately 350 nm or more, particularly 400 nm or more), but has a low sensitivity to light having a short wavelength. Therefore, when receiving light of a short wavelength, sufficient light emission intensity is required.
  • the cerium-added lithium calcium aluminum fluoride (Ce: LiCaAlF 6 ) described in Patent Document 1 has an emission wavelength region of 280 to 320 nm, and is not suitable when a silicon photodiode is used as a photodetector.
  • Tb gadolinium oxysulfide
  • Tb terbium-added gadolinium oxysulfide
  • the effective atomic number of Tb: Gd 2 O 2 S is 61, which is very high compared to LiCaAlF 6 (effective atomic number 14), lithium strontium aluminum fluoride [LiSrAlF 6 (effective atomic number 30)], and the like. That is, it is sensitive to ⁇ rays. Therefore, when Tb: Gd 2 O 2 S is used, it is difficult to detect only neutron beams.
  • An object of the present invention is to provide a scintillator for detecting a neutron beam, in which a silicon photodiode emits fluorescence having a wavelength with high sensitivity, has a relatively small effective atomic number, and hardly emits light due to ⁇ rays.
  • the inventors of the present invention prepared fluoride single crystals with various compositions and measured the emission spectrum at the time of ⁇ -ray excitation with a CCD comprising a silicon photodiode in order to evaluate the performance as a scintillator for neutron beam detection.
  • a scintillator for neutron beam detection comprising a cordierite type fluoride single crystal containing at least one kind of fourth periodic element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn
  • fourth periodic element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn
  • At least one fourth periodic element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn is contained, and further 6 Li is added to 0.80 atom / nm.
  • a scintillator for detecting a neutron beam comprising a cordierite type fluoride single crystal containing 3 or more is provided.
  • the basic structure of the Kolkyrite type fluoride single crystal has the following chemical formula: M X M Y M Z F 6
  • M X is at least one element necessarily including Li, Li, Na, K, selected Ri by the group consisting of Rb and Cs
  • M Y is at least one element Ca, Mg, Ba, Sr, selected from the group consisting of Cd and Be
  • M Z is, Al, which is at least one element such that selected from the group consisting of Ga and In
  • the basic structure of the cordierite-type fluoride single crystal is any compound selected from the group consisting of LiCaAlF 6 , LiSrAlF 6 and LiCa 1-x Sr x AlF 6 (0 ⁇ x ⁇ 1).
  • a neutron beam detection apparatus comprising the neutron beam detection scintillator and a photodetector.
  • the photodetector is a silicon photodiode.
  • the neutron beam detection scintillator of the present invention emits fluorescence that can be received by a silicon photodiode.
  • Silicon photodiodes are small and lightweight. Therefore, the combination of the scintillator and the silicon photodiode is useful as a small and lightweight neutron beam detector that can be used for determining the presence or absence of neutron beams in the environment.
  • the neutron beam detection apparatus is suitable for applications such as survey meters.
  • This figure is the schematic of the manufacturing apparatus by the micro pulling-down method of the crystal
  • This figure is a schematic diagram of a method for detecting ⁇ -ray excited luminescence of the scintillator for neutron beam detection according to the present invention.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Examples 1 and 2 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillators of Examples 3 and 4 by ⁇ ray excitation.
  • This figure is the emission spectrum by the alpha ray excitation of the scintillator for neutron beam detection of Examples 5 and 6.
  • This figure is an emission spectrum of the neutron beam detection scintillators of Examples 7 and 8 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillators of Examples 9 and 10 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillators of Examples 11 and 12 by ⁇ -ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillators of Examples 13 and 14 by ⁇ ray excitation.
  • This figure is the emission spectrum by the alpha ray excitation of the scintillator for neutron beam detection of Examples 15 and 16.
  • This figure is an emission spectrum of the neutron beam detection scintillators of Examples 17 and 18 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Example 19 by ⁇ -ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Example 20 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Example 21 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Example 22 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Example 23 by ⁇ ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Example 24 by ⁇ -ray excitation.
  • This figure is an emission spectrum of the neutron beam detection scintillator of Example 25 by ⁇ -ray excitation.
  • This figure is a schematic diagram showing a neutron beam detection apparatus provided with a scintillator for neutron beam detection and a photodiode according to the present invention.
  • This figure is a diagram showing current-voltage characteristics when light emitted when a thermal neutron beam is irradiated to the neutron beam detection scintillator of Example 16 is received by a silicon photodiode.
  • This figure is a diagram showing current-voltage characteristics when the silicon neutron beam receives light emitted when the scintillator for detecting neutron beam of Example 18 is irradiated with a thermal neutron beam.
  • This figure is a diagram showing current-voltage characteristics when the silicon neutron beam receives light emitted when a thermal neutron beam is irradiated to the neutron beam detection scintillator of Example 19.
  • This figure is a schematic view showing a neutron beam detection apparatus provided with a scintillator for neutron beam detection and a photomultiplier tube of the present invention.
  • This figure is a pulse height distribution spectrum diagram when a thermal neutron beam is irradiated to the neutron beam detector provided with the scintillator for neutron beam detection and the photomultiplier tube of Example 19.
  • the neutron beam detection scintillator of the present invention is at least one fourth periodic element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn (hereinafter referred to as “contained in the present invention”). 4), and a cordierite fluoride single crystal containing 6 Li of 0.80 atom / nm 3 or more.
  • corkyrite means a naturally occurring LiCaAlF 6 compound and has a specific crystal structure.
  • the corklite type is a compound having a structure similar to that of corkolite, and includes compounds in which elements in the compound are partially replaced with other elements.
  • the cordierite-type fluoride single crystal is preferably a crystal having a basic structure of a single crystal of a compound represented by the chemical formula M X M Y M Z F 6 (hereinafter, M X M Y the single crystal of compound according to formula of M Z F 6 may be referred to as a Korukiraito type basic structure crystal).
  • M X always including Li, Li, at least one element Na, K, is selected from the group consisting of Rb and Cs
  • M Y is selected from the group consisting Ca, Mg, Ba, Sr, from Cd and Be at least one element
  • M Z is, Al, represents at least one element selected from the group consisting of Ga and in.
  • M X always include Li required to detect neutron radiation, preferably includes a Na When performing charge adjustment.
  • M X , M Y and / or M Z in the compound represented by M X M Y M Z F 6 are , Partly replaced by a fourth periodic element.
  • the single crystal is a hexagonal crystal belonging to the space group P31c, and can be easily identified by a powder X-ray diffraction technique.
  • a single crystal represented by the chemical formula of LiCaAlF 6 , LiSrAlF 6 , LiCa 1-x Sr x AlF 6 (0 ⁇ x ⁇ 1) produced a large crystal. It is preferable in that it is easy and has high light emission intensity when used as a scintillator. In particular, LiCaAlF 6 is most preferable because it has a small effective atomic number, that is, low sensitivity to ⁇ rays.
  • the cordierite-type fluoride single crystal used in the present invention includes at least one kind of fourth crystal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn in the cordierite-type basic structure crystal.
  • the fourth periodic element is contained in the crystal lattice of M X M Y M Z F 6 by substituting any element of M X , M Y , and M Z.
  • the Mn element M Y, Cr element to replace the M Z.
  • the content of the fourth periodic element is 0.01 mol% or more with respect to the single crystal compound having the basic structure, it is preferable because high emission intensity can be obtained at the time of neutron irradiation, and 0.1 mol% or more. If it exists, since higher luminescence intensity is obtained at the time of neutron irradiation, it is more preferable. Moreover, when there is too much content, the phenomenon that light emission intensity falls by the overlap of the light emission wavelength and absorption wavelength of this 4th period element becoming large, ie, concentration quenching, may occur. Therefore, the upper limit of the content is preferably 10 mol% or less, more preferably 5 mol% or less in the case of Ti, V, Fe, Co, Ni and Cu. In the case of Cr, Mn, and Zn, 50 mol% or less is preferable and 20 mol% or less is more preferable.
  • the cordierite-type fluoride single crystal used in the present invention may contain at least one kind of rare earth element in addition to the fourth periodic element.
  • the rare earth element is presumed to be present between the crystal lattices of the cordierite-type basic structure crystal or a part of the element constituting the crystal, but the exact form of existence is unknown.
  • the rare earth elements are Ce, Eu, Pr, Nd, Er, Tm, Ho, Dy, Tb, Gd, Sm, Yb, La, Lu, Y, Sc, and Pm.
  • a cordierite fluoride single crystal By including a rare earth element, it is possible to obtain a cordierite fluoride single crystal in which light emission in a specific wavelength region is increased or the light emission wavelength region is widened.
  • a neutron detection scintillator made of a crystal with an extended emission wavelength region can be combined with a plurality of photodetectors having sensitivity to light in different wavelength regions. Specifically, when elements other than Ce and Eu are contained, light emission having a plurality of peak wavelengths can be obtained.
  • a cordierite type fluorine light having an increased light emission in a wavelength region of 350 nm or more, which is mainly sensitive to silicon photodiodes. Compound single crystals can be obtained.
  • the cordierite-type fluoride single crystal when a rare-earth element other than Ce and Eu is included in the cordierite-type fluoride single crystal, the sensitivity when combined with a silicon photodiode is improved as compared with the case where it is not included.
  • Ce and Eu when Ce and Eu are contained, a cordierite-type fluoride single crystal having emission of a wavelength of 290 to 370 nm included in a wavelength region where the photomultiplier tube is sensitive can be obtained. Therefore, the cordierite fluoride single crystal containing Ce and Eu in addition to the fourth periodic element can be combined with not only a silicon photodiode but also a photomultiplier tube.
  • Silicon photodiode and photomultiplier tube are photodetectors having different characteristics.
  • a silicon photodiode is smaller and lighter than a photomultiplier tube, but has a difference in that the amplification factor is low and the response speed is slow.
  • silicon photodiodes are strong against magnetic fields but weak against vibrations.
  • photomultiplier tubes are weak against magnetic fields but strong against vibrations. Therefore, silicon photodiodes and photomultiplier tubes can be used for different purposes.
  • a silicon photodiode is suitable as a medical radiation detector used in the vicinity of an MRI (nuclear magnetic resonance imaging) apparatus that generates a strong magnetic field, and as a radiation detector mounted on an excavator for logging in resource exploration.
  • MRI magnetic resonance imaging
  • a photomultiplier tube is suitable. Since these photodetectors have different wavelength ranges with high light receiving sensitivity, neutron beam scintillators that can be suitably used for both are limited in the scenes that can be used, for example, those having deliquescence. Other than that, little is known. However, such a material has high versatility and is very useful industrially.
  • the rare earth element content is preferably 0.005 mol% or more because high emission intensity is easily obtained upon irradiation with neutron radiation, and more preferably 0.02 mol% or more because higher emission intensity is easily obtained. Moreover, since there exists a tendency for the growth of a single crystal to become difficult when there is too much content of rare earth elements, it is preferable that content is 5 mol% or less.
  • the 6 Li content of the cordierite-type fluoride single crystal used in the present invention is preferably 0.80 atom / nm 3 or more. This is because the sensitivity to neutron beams necessary for use as a scintillator for detecting neutron beams is obtained. Furthermore, in order to increase the sensitivity to neutron rays, it is particularly preferable to the 6 Li content 4atom / nm 3 or more.
  • the upper limit of the 6 Li content is 9 atoms / nm 3 .
  • the 6 Li content that can be contained in the cordierite-type fluoride single crystal is theoretically about 9 atom / nm 3 at the maximum, and a 6 Li content higher than this cannot be obtained.
  • the 6 Li content means the number of 6 Li elements contained per 1 nm 3 of the scintillator.
  • the incident neutron beam causes a nuclear reaction with the 6 Li to generate ⁇ rays. Therefore, the 6 Li content affects the sensitivity to neutron beams, and the sensitivity to neutron beams increases as the 6 Li content increases.
  • Such 6 Li content select a suitable for the composition of the crystalline compound which is a basic structure of the scintillator, or, it can be appropriately adjusted by adjusting the content ratio of 6 Li of LiF or the like used as the Li raw material.
  • the existence ratio of 6 Li a presence ratio of 6 Li for all Li, existence ratio of natural is about 7.6%.
  • a method for adjusting the abundance ratio of 6 Li a general-purpose raw material having 6 Li in a natural abundance ratio is used as a starting material, and the concentration is adjusted to the desired 6 Li abundance ratio, or the intended 6 There is a method in which a concentrated raw material concentrated to a ratio higher than the Li existing ratio is prepared, and the concentrated raw material and the general-purpose raw material are mixed and adjusted.
  • the scintillator for detecting a neutron beam of the present invention is made of a single crystal, it does not cause loss due to non-radiative transition caused by lattice defects or scintillation light dissipation at the crystal grain boundary, and has high emission intensity.
  • the cordierite-type fluoride single crystal used in the present invention is a transparent crystal that is colorless or slightly colored and has excellent scintillation light transmission. In addition, it has good chemical stability, and under normal conditions of use, no performance degradation is observed in a short period of time. Furthermore, mechanical strength and workability are also good, and it is easy to process and use it in a desired shape.
  • the production method of the corklite-type fluoride single crystal used in the present invention is not particularly limited and can be produced by a known method, but is preferably produced by the Czochralski method or the micro pull-down method. This is because a cordierite-type fluoride single crystal excellent in quality such as transparency can be produced.
  • the micro pull-down method the crystal can be directly manufactured into a specific shape and can be manufactured in a short time.
  • the Czochralski method a large crystal having a diameter of several inches can be manufactured.
  • the micro pulling-down method is a method for producing a crystal by drawing a raw material melt from a hole provided in the bottom of the crucible 5 using an apparatus as shown in FIG.
  • a predetermined amount of raw material is filled into a crucible 5 having a hole at the bottom.
  • the shape of the hole is not particularly limited, but is preferably a cylindrical shape having a diameter of 0.5 to 4 mm and a length of more than 0 mm and 2 mm or less.
  • a cordierite type fluoride single crystal used in the present invention as raw materials, M X F, M Y F 2 , M Z F 3 , and a fluoride of the fourth periodic element contained in the present invention,
  • a fluoride of the rare earth element When at least one kind of rare earth element is contained, it is preferable to use a fluoride of the rare earth element.
  • the purity of these raw materials is not particularly limited, but each is preferably 99.99% or more.
  • the mixed raw material may be used in the form of powder or granules, or may be used after being sintered or melted and solidified in advance.
  • the LiF raw materials always contained in M X F, from the viewpoint of easily adjusting the 6 Li content of the scintillator, it is preferable to use a material obtained by concentrating a 6 Li.
  • Concentration levels as long as 6 Li content of the scintillator is at a concentration such that 0.8atom / nm 3 or more, is not particularly limited, the more the content of 6 Li in the scintillator, neutrons were grown crystal since the neutron detection efficiency when used as a line for detecting scintillator higher, concentrated concentration such that the content is increased in 6 Li in the scintillator is preferred.
  • the fluoride of the fourth periodic element and the fluoride of the rare earth element contained in the present invention can be blended so as to have a content in the above-mentioned range on the basis of M X M Y M Z F 6 .
  • the weighed value of at least one fluoride raw material powder of M X , M Y , and M Z substituted by the additive element may be reduced by the blending amount.
  • the blending amount of the fourth period element fluoride and the rare earth element fluoride used in the present invention may be set larger than the target content in consideration of the segregation phenomenon.
  • the segregation coefficient used when calculating the content of the actual additive element from the blending amount varies depending on the growth conditions such as the type of additive element and the growth rate, so the actual concentration should be examined by elemental analysis for each crystal production condition. It is preferable to determine.
  • the crucible 5 filled with the raw materials, the after heater 1, the heater 2, the heat insulating material 3, and the stage 4 are set as shown in FIG.
  • an inert gas such as high purity argon is introduced into the chamber 6 to perform gas replacement.
  • the pressure in the chamber after gas replacement is not particularly limited, but atmospheric pressure is common.
  • the gas replacement operation can remove moisture adhering to the raw material or the chamber, and can prevent deterioration of crystals derived from such moisture.
  • a solid scavenger such as zinc fluoride or a gas scavenger such as tetrafluoromethane.
  • a method in which the scavenger is premixed in the raw material is suitable.
  • a gas scavenger a method of mixing the scavenger with the inert gas and introducing it into the chamber is preferable.
  • the raw material After performing the gas replacement operation, the raw material is heated and melted by the high-frequency coil 7, and the melted raw material melt is drawn out from the hole at the bottom of the crucible to start crystal growth.
  • a metal wire is pulled down and provided at the tip of the rod.
  • the metal wire is inserted into the crucible through the hole at the bottom of the crucible, and the raw material melt is attached to the metal wire. After the adhesion, the raw material melt is pulled down together with the metal wire, so that crystals can be grown.
  • the metal wire is inserted into the hole at the bottom of the crucible and pulled out. This operation is repeated until the raw material melt is drawn together with the metal wire, and crystal growth is started.
  • the material of the metal wire can be used without limitation as long as it is a material that does not substantially react with the raw material melt. However, a material excellent in corrosion resistance at high temperatures such as a W-Re alloy is preferable.
  • the crystal After pulling out the raw material melt with the metal wire, the crystal can be obtained by continuously pulling it down at a constant pulling rate.
  • the pulling speed is not particularly limited, but if it is too fast, the crystallinity tends to be poor, and if it is too slow, the crystallinity is improved, but the time required for crystal growth becomes enormous, so 0.5 to 10 mm. A range of / hr is preferred.
  • an annealing operation may be performed after the production of the single crystal for the purpose of removing crystal defects caused by thermal strain.
  • the obtained single crystal can be easily processed into a desired shape.
  • a known cutting machine such as a blade saw or a wire saw, a grinding machine, or a polishing machine can be used without any limitation.
  • the single crystal can be used as a scintillator by processing and polishing the single crystal into an appropriate shape for the photodetector.
  • the shape of the scintillator for detecting a neutron beam according to the present invention is not particularly limited, but it is preferable that it has a light exit surface facing a photodetector described later, and the light exit surface is optically polished. By having such a light emitting surface, light generated by the scintillator can be efficiently incident on the photodetector.
  • the shape of the light emitting surface is not limited, and a shape according to the application such as a quadrangle with a side length of several mm to several hundred mm square or a circle with a diameter of several mm to several hundred mm is appropriately selected. Can be used.
  • the thickness of the scintillator with respect to the incident direction of the neutron beam varies depending on the energy of the neutron beam to be detected, but is generally several hundred ⁇ m to several hundred mm.
  • a light reflecting film made of aluminum, Teflon (registered trademark) or the like is preferable to apply to the surface not facing the photodetector. This is to prevent the dissipation of light generated by the scintillator.
  • the light emission of the scintillator for neutron beam detection according to the present invention can be detected by decomposing light into a spectrum using an arbitrary diffraction grating and CCD and measuring the spectrum.
  • a CCD is a type of photodetector that includes a plurality of photodiodes. Any CCD can be used, but in consideration of the wavelength at which light can be received, the type of photodiode constituting the CCD is preferably a silicon photodiode.
  • An electrical signal output from the CCD may be input to a personal computer via an arbitrary interface and analyzed. Such a spectroscopic detection method is preferable in that it easily separates an electric signal due to light emission of the scintillator and an electric signal due to noise.
  • the neutron beam detection scintillator of the present invention can be combined with a photodetector to form a neutron beam detector.
  • the presence and intensity of a neutron beam can be captured by converting light (scintillation light) emitted from a neutron beam detection scintillator by irradiation with a neutron beam into an electrical signal by a photodetector.
  • the scintillation light emitted from the scintillator of the present invention varies depending on the additive element, the scintillation light includes light having a sensitivity of 350 nm or more with which the silicon photodiode has sensitivity.
  • Examples of the photodetector include a photodiode and a photomultiplier tube.
  • the wavelength dependence of the sensitivity of the photodetector varies depending on the type.
  • a silicon photodiode is generally highly sensitive to light having a wavelength of 350 nm or more, particularly 400 nm or more.
  • the scintillator for detecting a neutron beam of the present invention can be suitably used in combination with a photodiode, particularly a silicon photodiode, because it can emit light having a long wavelength of 350 nm or longer.
  • the wavelength dependency of the sensitivity varies depending on the material of the photoelectric material and the photoelectric window. Therefore, it is necessary to select the type of photomultiplier tube to be used according to the emission wavelength of the scintillator.
  • the photodiode can be suitably used for a small and lightweight neutron beam detector.
  • an APD avalanche photodiode having an electric signal amplification function is preferably used in that the light of the scintillator can be received with high sensitivity.
  • an avalanche photodiode S8664 series manufactured by Hamamatsu Photonics can be used.
  • the neutron beam detection apparatus of the present invention can be obtained by bonding the scintillator for neutron beam detection of the present invention and the light receiving surface of the photodiode with an arbitrary optical grease such as silicon grease.
  • the light-receiving surface of the photodiode to which the scintillator of the present invention is bonded may be covered with a light-shielding material of any material that is difficult to transmit light for the purpose of preventing the incidence of light in the environment.
  • the surface other than the surface bonded to the photodiode may be covered with a reflecting material made of aluminum, Teflon (registered trademark), barium sulfate, or the like to increase the light collection efficiency.
  • the detection device may have the function of both a material and a reflective material, and may cover the entire detection device.
  • the detection device can be connected to an arbitrary current measuring device (for example, a picoammeter) to check the change in the current value, and the change in the current value according to the change in the amount of received light can be confirmed.
  • a voltage may be applied to the silicon photodiode in a reverse bias, and in that case, any measuring instrument capable of simultaneously applying and measuring voltage or current (for example, KEITLEY 237, HIGH VOLTAGE SOURCE MEASURE UNIT may be used.
  • the voltage value to be applied is preferably set according to the performance of the silicon photodiode and the flux of neutron to be measured.
  • the scintillator and the light-receiving surface of the photomultiplier tube are bonded with an arbitrary optical grease or the like, as in the case of the photodiode.
  • a neutron beam detector can be obtained.
  • the light receiving surface of the photomultiplier tube to which the scintillator of the present invention is bonded may be covered with a light shielding material made of any material that is difficult to transmit light for the purpose of preventing the incidence of light in the environment.
  • the scintillator of the present invention may be covered with a reflective material made of aluminum, Teflon (registered trademark), barium sulfate, or the like, except for the adhesive surface with the photomultiplier tube.
  • the whole may be covered with the material function.
  • the sensitivity of the photomultiplier tube is increased by applying a high voltage, and the detection of the neutron beam can be confirmed by observing the electric signal output from the photomultiplier tube.
  • the electrical signal output from the photomultiplier tube may be input to an ammeter such as a picoammeter, the current-voltage characteristics may be evaluated, and the change in the amount of current may be confirmed to determine the intensity of the neutron beam. Further, the output electric signal may be input to an amplifier, a multi-wave height analyzer or the like and measured by photon counting (photon counting method).
  • photon counting photon counting method
  • a photodetector a silicon photodiode array or a position sensitive photomultiplier tube in which detectors having a sensitive area of several mm square are arranged in an array is used to cover part or all of the photocathode.
  • a neutron beam imaging device by joining the scintillator of this invention.
  • the scintillator may have an arbitrary shape, and can be a scintillator array in which plate-shaped, block-shaped, or quadrangular prism-shaped crystals are regularly arranged.
  • the electrical signal output from the silicon photodiode array or the position sensitive photomultiplier tube can be read out using an arbitrary interface, and may be controlled by a personal computer using a control program.
  • Example 1 Manufacture of neutron beam scintillators
  • mold fluoride single crystal in Example 1 is demonstrated.
  • Examples 2 to 25 were prepared in the same manner except that the type of element to be added and the raw material weighed value were different.
  • a cordierite type fluoride single crystal used in the present invention was produced.
  • the cordierite-type basic structure crystal was LiCaAlF 6 and Cu was used as the fourth periodic element.
  • As the raw material purity of 99.99% or more LiF, a highly purified fluoride powder of CaF 2, AlF 3, CuF 2 .
  • As the LiF 6 Li content ratio was used as 95%.
  • the after heater 1, the heater 2, the heat insulating material 3, the stage 4, and the crucible 5 are made of high-purity carbon, and the shape of the hole provided at the bottom of the crucible is a circle having a diameter of 2.2 mm and a length of 0.5 mm. It was columnar.
  • the crucible 5 was filled with the obtained mixed raw material.
  • the crucible 5 filled with the raw material was set on the upper part of the after heater 1, and the heater 2 and the heat insulating material 3 were sequentially set around the crucible.
  • the inside of the chamber 6 is evacuated to 5.0 ⁇ 10 ⁇ 4 Pa by using an evacuation apparatus composed of an oil rotary pump and an oil diffusion pump, and then a large amount of mixed gas of tetrafluoromethane and argon is introduced into the chamber 6. The gas was replaced by introducing the pressure up to atmospheric pressure.
  • a high frequency current was applied to the high frequency coil 7, and the raw material was heated and melted by induction heating.
  • a W-Re wire provided at the tip of the pull-down rod 8 was inserted into the hole at the bottom of the crucible 5, and the raw material melt was pulled down from the hole to start crystallization. While adjusting the output of the high frequency, it was continuously pulled down at a speed of 3 mm / hr for 17 hours to obtain a cordierite type fluoride single crystal used in the present invention.
  • the crystal had a diameter of 2.1 mm and a length of 60 mm, and had good quality without white turbidity or cracks.
  • the crystal is cut to a length of 10 mm by a wire saw equipped with a diamond wire, and then ground and mirror-polished, and processed into a shape having a length of 7 mm, a width of 2 mm, and a thickness of 1 mm. A scintillator was obtained.
  • the 6 Li abundance ratio of the lithium raw material of the scintillator was 95%, and the density and molecular weight of LiCaAlF 6 were 3.0 g / cm 3 and 188 g / mol, respectively. Substituting these values into equation for calculating the 6 Li content above [1], 6 Li content was 8.3atom / nm 3. The amount of Cu added to the neutron beam scintillator was 0.5 mol% with respect to LiCaAlF 6 , and the calculated effective atomic number was about 15.
  • Examples 2 to 25 For Examples 2 to 25, each material was weighed according to Table 1 below, and crystals were prepared, cut and polished in the same manner as in Example 1 except that the materials were added, and the neutron beam detection scintillator of the present invention was used. Obtained. In either embodiment, 6 Li content of the scintillator is 8.3atom / nm 3, the effective atomic number calculated was about 15.
  • a 241 Am sealed radiation source 10 is installed in the vicinity of the neutron beam detection scintillator 9, irradiated with ⁇ rays, and the scintillation light 11 generated by excitation is incident on the CCD spectrometer 12.
  • the 241 Am sealed radiation source 10 one having a radioactivity of 4 MBq was used.
  • the CCD spectroscope 12 a spectroscope (KV-MV type spectroscope manufactured by Spectrometer Co., Ltd.) having a structure in which incident light is split by a diffraction grating and received by a CCD is used.
  • the spectrometer was equipped with a newton manufactured by ANDOR TECHNOLOGY as a CCD, and a silicon photodiode was used for the CCD.
  • 3 to 18 show the emission spectra of Examples 1 to 25 obtained.
  • the horizontal axis indicates the emission wavelength, and the vertical axis indicates the emission intensity. Although each has a different emission wavelength, it contains light of 350 nm or more and was found to emit light with a light emission intensity detectable by the CCD.
  • the scintillator of this invention light-emits when the alpha ray produced by the nuclear reaction of a thermal neutron beam and 6 Li excites a luminescent center element, and can be used as a scintillator for neutron beam detection.
  • an avalanche photodiode (S8664-1010 manufactured by Hamamatsu Photonics) having sensitivity to light in a wavelength region of about 350 nm to 1000 nm was used.
  • the neutron beam detection scintillator 9 of the present invention was adhered to the light receiving surface of the diode 13 with silicon grease and covered with a light shielding material 14 made of a black vinyl sheet to obtain the neutron beam detection apparatus of the present invention.
  • the detection device was used in connection with an ammeter 15.
  • the ammeter 15 is a KEITLEY 237 HIGH VOLTAGE SOURCE MEASURE UNIT that can read the current value while applying a voltage, and the current value while applying a voltage of 300 to 400 V with a reverse bias under the control of a program on a personal computer.
  • the current-voltage characteristic graph was drawn.
  • FIG. 20 shows a case where a neutron beam detector of the present invention comprising the scintillator of Example 16 is directly irradiated with a thermal neutron beam and a case where a shield plate is installed between the thermal neutron beam source and the detector. Shows current-voltage characteristics.
  • a Cd (cadmium) 1 mm thick plate having high absorption efficiency for thermal neutron rays was used to reduce the flux of thermal neutrons irradiated to the scintillator.
  • the current value at 350 V was 1.24 ⁇ 10 ⁇ 8 A when the thermal neutron beam was shielded, whereas it was 1.53 ⁇ 10 ⁇ 8 A when the thermal neutron beam was not shielded. It was found that the current value increased with increasing neutron flux.
  • a neutron beam detector was prepared in the same manner as described above using the scintillators of Examples 18 and 19 instead of the scintillator of Example 16, and the current-voltage characteristics of the device were measured. The results are shown in FIGS. In both cases, the current value increased due to thermal neutron irradiation.
  • thermal neutron radiation can be detected by combining the scintillator for detecting neutron radiation of the present invention and a silicon photodiode.
  • FIG. 23 shows the configuration of the neutron beam detection apparatus of the present invention.
  • the photomultiplier tube 16 R7600U manufactured by Hamamatsu Photonics Co., Ltd. having sensitivity to light of about 250 nm to 750 nm was used.
  • the neutron beam detection scintillator 9 the scintillator of Example 19 was used. After the surface of the scintillator having a length of 7 mm and a width of 2 mm was adhered to the photocathode of the photomultiplier tube 16 with optical grease, the scintillator was shielded from light with a light shielding material 14 made of a black vinyl sheet so that light from the outside did not enter.
  • the thermal neutron radiation source a 252 Cf sealed radiation source placed in a polyethylene container was used.
  • scintillation light emitted from the scintillator was measured by a photon counting method.
  • the scintillation light was converted into an electric signal through the photomultiplier tube 16 to which a high voltage of 600 V was applied.
  • the electric signal output from the photomultiplier tube 16 is a pulse-like signal reflecting the scintillation light
  • the pulse height represents the emission intensity of the scintillation light
  • the waveform thereof is obtained when the scintillation light is attenuated.
  • FIG. 24 shows pulse height distribution spectra when the neutron beam detector is directly irradiated with a thermal neutron beam and when a shield plate is installed between the thermal neutron beam source and the neutron beam detector.
  • a Cd plate having a thickness of 1 mm was used in order to reduce the thermal neutron flux.
  • the horizontal axis of the pulse height distribution spectrum represents the peak value of the electric signal, that is, the emission intensity of the scintillation light. Further, the vertical axis represents the frequency of the electric signal indicating each peak value, and here, it is indicated by the number of times (counts) the electric signal is measured.
  • the neutron beam detection scintillator of the present invention has a sufficient light emission amount. From the above, it has been found that the neutron beam detection scintillator of the present invention operates as a neutron beam detector even when combined with a photomultiplier tube as well as a silicon photodiode.

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Abstract

La présente invention concerne un scintillateur utilisé dans la détection de faisceau de neutrons et qui comprend un monocristal de fluorure de type colquiriite et contenant au moins un élément de la période 4 sélectionné dans le groupe comprenant Ti, V, Cr, Mn, Fe, Co, Ni, Cu, et Zn, par exemple du type représenté par la formule générale MXMYMZF6 (MX contient Li obligatoirement, et représente Li, Na, etc; MY représente Ca, Mg, etc.; et MZ représente Al, Ga, etc.), et contenant au moins 0,80 atom/nm3 de 6Li; et un dispositif de détection de faisceau de neutrons pourvu du scintillateur et d'un photodétecteur. Le scintillateur utilisé dans la détection de faisceau de neutrons émet une lumière fluorescente d'une longueur d'onde à laquelle des photodiodes de silicium ont une sensibilité élevée, et le numéro atomique efficace est relativement petit, et il est donc difficile de générer une émission de lumière au moyen des rayons gamma.
PCT/JP2012/052526 2011-02-03 2012-02-03 Scintillateur pour la détection de faisceau de neutrons et dispositif de détection de faisceau de neutrons WO2012105694A1 (fr)

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WO2004086089A1 (fr) * 2003-03-24 2004-10-07 Hokushin Corporation Materiau monocristal fluorure pour dosimetre thermoluminescent et dosimetre thermoluminescent associe
WO2009119378A1 (fr) * 2008-03-24 2009-10-01 株式会社トクヤマ Scintillateur pour la détection de neutrons et détecteur de neutrons
JP2010181373A (ja) * 2009-02-09 2010-08-19 Tokuyama Corp 放射線検出装置及び放射線の検出方法

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WO2004086089A1 (fr) * 2003-03-24 2004-10-07 Hokushin Corporation Materiau monocristal fluorure pour dosimetre thermoluminescent et dosimetre thermoluminescent associe
WO2009119378A1 (fr) * 2008-03-24 2009-10-01 株式会社トクヤマ Scintillateur pour la détection de neutrons et détecteur de neutrons
JP2010181373A (ja) * 2009-02-09 2010-08-19 Tokuyama Corp 放射線検出装置及び放射線の検出方法

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A.GEKTIN ET AL.: "LiCaAlF6:Ce crystal: a new scintillator", NUCLEAR INSTRUMENTS AND METHODS IN PHYSICS RESEARCH A, vol. 486, 21 January 2002 (2002-01-21), pages 274 - 277 *
S.NEICHEVA ET AL.: "Energy transfer features in Eu2+ and Ce3+ doped LiCaAlF6 crystals", RADIATION MEASUREMENTS, vol. 42, 1 February 2007 (2007-02-01), pages 811 - 814 *

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