JP2015169455A - Radiation measurement method, collimator and radiation measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily and accurately measuring a radiation radiating from a radioactive substance existing in a deeper part than the surface of a measurement object, and an apparatus and device used for the same.SOLUTION: A radiation measurement method which measures a radiation radiating from a radioactive substance 102 existing in a deeper part 112 than a surface 110 of a measurement object 100 performs first measurement for measuring a radiation Rp which radiates from the deeper part 112 and whose passage distance from the deeper part 112 to the surface 110 is a first length L1 and second measurement for measuring a radiation Rs which radiates from the deeper part 112 and whose passage distance from the deeper part 112 to the surface 110 is a second length L2 longer than the first length L1, and calculates the radioactivity characteristics in the deeper part 112 on the basis of the ratio of the measurement result in the first measurement to the measurement result in the second measurement.

Description

  The present invention relates to a radiation measurement method for measuring radiation radiated from a radioactive substance existing deeper than the surface of a measurement target, and a collimator and a radiation measurement apparatus used in the radiation measurement method.

  Various methods and devices for measuring the radioactivity of buildings and the ground contaminated with radioactive materials such as radioactive cesium have been proposed. As a representative method, there are known a method for obtaining radioactivity from an in-situ air dose rate using a survey meter and a method for counting beta rays.

  Non-Patent Document 1 describes measuring an air dose rate of gamma rays using a scintillation-type survey meter as a method for obtaining an index of the state of contamination by radioactive substances. However, since gamma rays fly not only from the measurement object such as soil but also from the surrounding four sides, the radioactivity of the measurement object cannot be accurately quantified even if the air dose rate is measured.

  Patent Document 1 describes a radioactive substance detection apparatus (radiation measurement apparatus) that counts characteristic X-rays originating from radioactive substances. This apparatus counts the characteristic X-rays incident from the measurement object by shielding the characteristic X-rays flying from the surroundings with respect to the sensing element directed to the measurement object without shielding the gamma rays.

International Publication No. 13/105519 Pamphlet

“Guidelines on Survey and Measurement Methods for Environmental Pollution Status in the Pollution Status Priority Survey Area” Ministry of the Environment, December 2011, 1st Edition

  The radioactive material that has come to the surface of the building or the ground penetrates into the interior together with rainwater and sinks deeper than the surface, affecting the dose on the surface. However, the depth position and settling velocity of radioactive materials vary depending on conditions, and the measurement requires a great amount of labor and time. On the other hand, as one of the typical decontamination work, the surface is cleaned, and it is required to measure the radioactivity of the radioactive substance located inside in order to quantify the decontamination effect. Yes.

  On the other hand, since beta rays are greatly absorbed even by a shield with a thickness of about 1 mm of paper and the count rate is significantly reduced, the beta rays emitted from radioactive materials existing deeper than the surface are accurately detected on the ground surface. It cannot be measured.

  Also, with respect to the method of Patent Document 1, the characteristic X-ray has a lower transmission capability than the gamma ray, and a part thereof is shielded by the substance. For this reason, when the characteristic X-ray to be radiated is measured from the surface and converted into radioactivity, it may be underestimated as compared with the true radioactivity inside. Main gamma rays having high energy (hereinafter sometimes referred to as “main gamma rays”) are easily transmitted through the material and radiated from the surface, but are partially shielded as in the method of Patent Document 1. When X-rays are counted and converted to radioactivity, the radioactivity is underestimated.

  In addition, for example, as a method for quantitatively measuring the radioactivity of radioactive substances located in the deep part of the soil, the soil sample at each depth is measured by a boring test, but this test is extensive. Therefore, a large-scale facility is required and a long time is required for measurement.

  The present invention has been made in view of the problems as described above, and a method for easily and accurately measuring radiation emitted by a radioactive substance existing deeper than the surface of a measurement target, and an apparatus used for such a method, A device is provided.

  According to the present invention, there is provided a method for measuring radiation radiated from a radioactive substance existing deeper than a surface to be measured, wherein a first distance is a distance from the deep part to the surface that is emitted from the deep part. A first measurement for measuring radiation, and a second measurement for measuring radiation radiated from the deep part and having a second length that is longer than the first length by the distance from the deep part to the surface. And a radiation measurement method characterized in that the radioactivity characteristic in the deep part is calculated based on a ratio between the measurement result measured in the first measurement and the measurement result measured in the second measurement. .

  Further, according to the present invention, there is provided a collimator used in the radiation measurement method described above, the attachment part attached to the radiation measurement apparatus including a detection element for detecting radiation, and the attachment part attached to the radiation measurement apparatus. An inclined opening that opens in a direction inclined with respect to the detection direction of the detection element, and an average incident angle with respect to the detection direction of the radiation incident on the inclined opening is equal to or less than a predetermined value A collimator is provided that shields the radiation.

  Further, according to the present invention, there is provided a directivity measurement device that includes a collimated detection element that detects a photon, and that measures radiation emitted by a radioactive substance that exists deeper than the surface of the measurement target. The collimating direction of the element is variable or selectable, and the first measurement that measures the radiation that is radiated from the deep part and the passing distance from the deep part to the surface is the first length; A radiation measurement apparatus is provided that performs a second measurement of measuring radiation having a second length that is longer than the first length by a passing distance from a deep part to the surface.

  According to the said invention, many radiation radiated | emitted in all directions from the radioactive substance which exists in a predetermined depth position is measured in the state from which the passage distance from a deep part to the surface differs. Thereby, the radiation radiated | emitted from the radioactive material which has the equivalent radioactivity in the deep part is measured by the attenuation rate which is different by the 1st measurement and the 2nd measurement. Therefore, by obtaining the ratio of these measurement results, the radioactivity characteristics such as the radioactivity in the deep part, the depth position, and the passage distance can be calculated.

  ADVANTAGE OF THE INVENTION According to this invention, the radiation which the radioactive substance which exists deeper than the surface of a measuring object radiates | emits can be measured easily and correctly.

It is a cross-sectional schematic diagram which shows the radiation measuring device of embodiment of this invention. (A) is explanatory drawing which shows the radiation which is shielded with a parallel collimator, and the radiation which injects into a detection element. (B) is explanatory drawing which shows the radiation which shields with a slant collimator, and the radiation which injects into a detection element. It is a schematic diagram which shows the radiation which injects into a detection element. (A) is a schematic diagram which shows the structure of the 1st measuring device used for the 1st Example, (b) is a schematic diagram which shows the structure of the 2nd measuring device used for the 1st Example. It is a radiation spectrum which shows the measurement result of a 2nd measurement. It is a graph which shows the state which fitted the radiation spectrum of the 2nd measurement with the approximate function. It is a graph which shows the relationship between the thickness of a shielding board, and the count rate of a characteristic X-ray. It is a graph which shows the relationship between the surface density of a shielding board and the count rate of a characteristic X-ray, and the relationship between the surface density of a shielding board, and the ratio of the measurement result of a 1st measurement and a 2nd measurement. It is a figure which shows the result of a 2nd Example, and is a graph which shows the relationship between the surface density depth of a measured object, and the ratio of the measurement result of a 1st measurement and a 2nd measurement.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same constituent elements are denoted by the same reference numerals, and redundant description is omitted as appropriate.

  FIG. 1 is a schematic cross-sectional view showing a radioactivity measurement apparatus (hereinafter sometimes abbreviated as a measurement apparatus) 10 according to an embodiment of the present invention. FIG. 1 shows a longitudinal section in which the measuring device 10 is cut along the directing direction of the sensing elements 20p and 20s. The measurement apparatus 10 is installed with the detection surface 22 of the detection elements 20p and 20s facing the surface 110 of the measurement target 100.

First, an outline of the present embodiment will be described.
The measurement apparatus 10 includes collimated detection elements 20p and 20s that detect photons, and a directional apparatus that measures the radiation Rp and Rs emitted by the radioactive substance 102 that exists in the deeper part 112 than the surface 110 of the measurement object 100. It is.
The collimating directions of the detection elements 20p and 20s can be changed or selected. The detection elements 20p and 20s may be collectively referred to as the detection element 20.
The measuring apparatus 10 of the present embodiment is characterized by performing a first measurement and a second measurement. In the first measurement, a radiation Rp that is radiated from the deep part 112 and whose passing distance from the deep part 112 to the surface 110 is the first length L1 is measured. In the second measurement, radiation Rs radiated from the deep portion 112 and having a second distance L2 from the deep portion 112 to the surface 110 is measured (see FIG. 3). The second length L2 is longer than the first length L1. The measuring apparatus 10 of this embodiment is used for the radiation measuring method described later.

  Next, the measuring apparatus 10 of this embodiment will be described in detail. In addition, as shown in FIG. 1, although this embodiment demonstrates the state by which the measuring object 100 is arrange | positioned below in the figure, the up-down direction of the figure does not necessarily mean the direction of gravity. However, for convenience, the side of the measuring device 10 on which the detection surface 22 is disposed is referred to as the front end side, the lower side or the lower end side, and the side on which the photoelectric conversion device 24 and the amplifier 26 are disposed is the base end side, above or It may be called the upper end side.

  The measuring device 10 is a directional device that measures the radioactivity of a radioactive substance that emits characteristic X-rays and gamma rays. Here, the radioactivity refers to a count rate or a radioactivity surface density of radiation radiated from the measurement object 100, or a numerical value that can be converted from these.

  Examples of the measurement object 100 include the ground (paved surface, soil surface), the wall surface of a building, the surface of a building such as a road surface and a gutter, and the bark surface of a tree. When the measuring object 100 is an upright surface like a wall surface of a building, the measurement direction of the measuring device 10 is the normal direction of the upright surface, for example, the horizontal direction.

  FIG. 1 illustrates a state in which the radioactive substance 102 is uniformly distributed in a planar manner in a deep portion 112 corresponding to a single depth position from the surface 110 of the measurement target 100. In addition, the radioactive substance 102 may be evenly distributed inside the measurement object 100 regardless of the depth position, or has an exponential function distribution in which the density gradually decreases in the depth direction with the surface 110 as the maximum value. May be.

  The measuring apparatus 10 includes a plurality of collimators 40p and 40s that are detachably attached to the detection elements 20p and 20s and have different collimating directions. The collimating direction of the collimators 40p and 40s is the depth direction of the opening 41, in other words, the direction connecting the opening 41 and the detection elements 20p and 20s. That the detection elements 20p and 20s are detachable from the detection elements 20p and 20s includes a state in which the collimators 40p and 40s are indirectly connected to the detection elements 20p and 20s through the housing 12 or the like.

  The measuring apparatus 10 includes a first measuring device 11p that performs a first measurement and a second measuring device 11s that performs a second measurement. The first measuring instrument 11p includes a collimator 40p and a detection element 20p, and the second measuring instrument 11s includes a collimator 40s and a detection element 20s. The first measuring instrument 11p and the second measuring instrument 11s have a common configuration except that the shapes of the collimators 40p and 40s and the collimating direction and the partial shape of the shield 30 are different. The first measuring device 11p and the second measuring device 11s may be collectively referred to as the measuring device 11.

  The first measuring instrument 11p and the second measuring instrument 11s count the radiation emitted from the close position that can be regarded as the same position or substantially the same position of the measurement object 100. Thereby, it can be considered that the depth of the deep part 112 in which the radioactive substance 102 exists is common in the position which the 1st measuring device 11p and the 2nd measuring device 11s each measure.

  In addition, in FIG. 1, the 1st measuring device 11p provided with the detection element 20p and the 2nd measuring device 11s provided with the detection element 20s are provided separately, and the aspect which can measure radiation Rp and Rs simultaneously is illustrated. However, the present invention is not limited to this. Instead of the present embodiment, the measuring apparatus 10 may perform the first measurement and the second measurement at different timings by alternately mounting the collimator 40p and the collimator 40s on one measuring device 11.

  Hereinafter, a configuration common to the first measuring instrument 11p and the second measuring instrument 11s (measuring instrument 11) will be described.

  The measuring instrument 11 includes a housing 12, a sensing element 20, a photoelectric conversion device 24, an amplifier 26 and a shield 30. In addition, the measurement apparatus 10 of this embodiment includes a gantry 70 and a data processing device 90.

  The detection element 20 detects photons of characteristic X-rays that enter the detection surface 22. The sensing element 20 can be an inorganic crystal scintillator. The inorganic crystal scintillator used for the sensing element 20 is not particularly limited. Thallium activated sodium iodide, cesium iodide, gadolinium silicate, lutetium silicate, bismuth germanate, cerium fluoride, barium fluoride, lead fluoride, lead tungstate, europium activated lithium iodide, europium activated iodine And strontium chloride. As cesium iodide, pure cesium iodide, thallium activated cesium iodide or sodium activated sodium iodide can be used.

  As the detection element 20, in addition to a scintillation detector, a proportional counter, a semiconductor detector, or the like can be used. The detection element 20 detects at least a characteristic X-ray of 30 keV or more and less than 40 keV emitted from barium originating from radioactive cesium. The detection element 20 may detect radiation of 40 keV or more and 1000 keV or less. Hereinafter, characteristic X-rays, gamma rays, and scattered gamma rays are collectively referred to as radiation.

  The sensing element 20 has a detection efficiency of 40% or more, preferably 50% or more for a characteristic X-ray of 30 keV or more and less than 40 keV. The detection element 20 has a detection efficiency of 50% or less, preferably 40% or less, for photons of 200 keV or higher. As described above, by giving the energy characteristic suitable for the characteristic X-ray, it is possible to reduce the influence of the scattered radiation gamma ray incident on the detection element 20. Specifically, when the sensing element 20 is NaI (Tl), the influence of scattered gamma rays can be significantly suppressed by setting the thickness to 5 mm or less. In terms of the detection efficiency of the detection element 20, this is achieved by setting the detection element 20 to a thickness that makes the detection efficiency 40% or less for a photon of 200 keV or higher.

  The half-life of radioactive cesium cesium 137 and cesium 134 is about 30 years and about 2 years, respectively. Cesium 137 decays to barium 137m with a short half-life due to beta decay, and then becomes non-radioactive barium. Cesium 134 disintegrates directly into non-radioactive barium 134. At the time of beta decay of radioactive cesium, orbital electrons are emitted instead of gamma rays, and barium emits characteristic X-rays when electrons fall into the holes. The characteristic X-ray energy of barium originating from radioactive cesium is 32.1 keV and 36.5 keV. The detection element 20 detects one or both of 32.1 keV and 36.5 keV, which are barium characteristic X-rays.

The photoelectric conversion device 24 is a device that converts light emitted when radiation (photons) enters the detection surface 22 of the detection element 20 into electric pulses that are electric energy. For the photoelectric conversion device 24, a photomultiplier tube or a photodiode can be used. In addition, when the detection element 20 is a semiconductor detector (solid state detector), the photoelectric conversion device 24 is unnecessary.
The amplifier 26 amplifies the electric pulse generated by the photoelectric conversion device 24. The amplifier 26 is provided with a signal terminal 27 for outputting the amplified electric pulse signal to the data processing device 90 and a power supply terminal 28 for power supply. The power supply terminal 28 is connected to a power supply device (not shown).

  The detection element 20, the photoelectric conversion device 24, and the amplifier 26 are accommodated in the housing 12. The housing 12 has a hollow cylindrical shape and is made of a thin metal plate. The detection element 20 is held at the tip of the housing 12.

(About shield)
The shield 30 is a member that reduces the incidence of scattered gamma rays and characteristic X-rays flying from directions different from the collimating directions of the collimators 40p and 40s from entering the detection elements 20p and 20s. The shield 30 is provided so as to surround at least the side periphery of the detection elements 20p and 20s. A region surrounding the side periphery of the detection elements 20p and 20s in the shield 30 is referred to as side peripheral portions 32p and 32s. The surface density of the side peripheral portions 32p and 32s is set in a range that transmits the main gamma rays originating from the radioactive material contained in the measurement object 100 and shields the scattered gamma rays and the characteristic X-rays that are the scattered rays of the gamma rays. .

  The side peripheral portion 32p attached to the first measuring instrument 11p has a straight cylindrical shape, and is attached to a region that covers a part of the collimator 40p, the detection element 20p, and the tip side of the photoelectric conversion device 24. The side peripheral portion 32 s attached to the second measuring instrument 11 s protects the periphery of the collimator 40 s having a larger diameter than the lower end of the housing 12, so that the open lower end side is connected to the base end portion 34. It is formed in a larger diameter than.

  The shield 30 may be made of an organic material in addition to an inorganic material such as metal or ceramic. As the metal material, heavy metals such as iron, stainless steel, lead or tungsten can be used.

  Specifically, the side peripheral portions 32p and 32s shield the scattered gamma ray peak of the radioactive substance so that the transmittance is less than 50%. Further, the transmittance of gamma rays of 60 keV or more and 300 keV or less to the side peripheral portions 32p and 32s is less than 50%.

When measuring radioactive cesium as a radioactive substance, the thickness of the shield 30 is preferably 0.7λ or more in terms of the mean free path (λ) of 300 keV gamma rays. The shielding ability of the shield 30 against gamma rays of 60 keV or more and 300 keV or less is preferably an area density of 2.2 g / cm ² or more in terms of lead. In other words, the shielding ability of the shielding body 30 against gamma rays in the above-described wavelength region is preferably equal to or more than the shielding ability of a lead plate (2 mm in terms of thickness) having a surface density of 2.2 g / cm ^2. . That is, when the shield 30 is made of lead, the surface density is preferably 2.2 g / cm ² or more (thickness 2 mm or more).

  As a result, scattered gamma rays originating from radioactive cesium are shielded with a transmittance of less than 50%. Since the characteristic X-rays originating from radioactive cesium have lower energy than the scattered gamma rays as described above, the characteristic X-rays are also shielded at a lower transmittance than the scattered gamma rays by using the shield 30 of this embodiment. The

The upper limit of the shielding ability of the shield 30 with respect to gamma rays of 60 keV or more and 300 keV or less is not particularly limited. Due to the demand for weight reduction of the measuring device 10, the surface density is 12 g / cm ² or less in terms of lead, 10 mm or less in terms of lead thickness, and 5 λ or less in terms of the mean free path (λ) of 300 keV gamma rays. preferable. More preferably, the upper limit of the shielding capability of the shield 30 is 6 g / cm ² or less in surface density in terms of lead, and 5 mm or less in terms of lead thickness. That is, when the shield 30 is made of lead, the surface density is preferably 6 g / cm ² or less (thickness 5 mm or less).

  The shield 30 transmits main gamma rays and shields scattered gamma rays and characteristic X-rays. As a result, the scattered gamma rays and characteristic X-rays flying from the collimating direction can be counted in a state where the scattered gamma rays and characteristic X-rays flying from the directions different from the collimating direction are shielded. Hereinafter, for convenience, a direction different from the collimating direction may be referred to as “side”. The main gamma rays that have traveled from the arbitrary direction and passed through the shield 30 are incident on the detection elements 20p and 20s. However, in general, the main gamma ray has a very high energy compared to the characteristic X-ray. For this reason, even if the main gamma rays are incident on the detection elements 20p and 20s, the main gamma rays and the characteristic X-rays can be easily distinguished from each other in the radiation energy spectrum (hereinafter referred to as the radiation spectrum).

  The shield 30 includes side peripheral portions 32p and 32s surrounding the side periphery of the detection element 20, and a base end portion 34 provided on the opposite side of the detection surface 22 with respect to the side peripheral portions 32p and 32s. I have. The surface density at the base end portion 34 can be made smaller than the surface density at the side peripheral portions 32p and 32s. A top surface portion 36 that covers a part of the base end side of the photoelectric conversion device 24 and the amplifier 26 is provided on the upper end side of the base end portion 34. The surface density of the top surface portion 36 can be made smaller than the surface density of the base end portion 34. As an example, in terms of lead, the thickness of the side peripheral portions 32p and 32s can be 5 mm, the thickness of the base end portion 34 can be 2 mm, and the thickness of the top surface portion 36 can be 1 mm. The side peripheral portion 32p and the side peripheral portion 32s can have a common surface density.

  The gantry 70 holds the measuring instrument 11 and arranges the detection element 20 so as to face the surface 110 of the measurement target 100. The specific mechanism and shape of the gantry 70 are not particularly limited. When using the 1st measuring device 11p and the 2nd measuring device 11s separately in the measuring apparatus 10, the mount frame 70 may hold | maintain both the 1st measuring device 11p and the 2nd measuring device 11s. Alternatively, the gantry 70 may be individually attached to the first measuring instrument 11p and the second measuring instrument 11s.

  The data processing device 90 is an external device that is connected to the signal terminal 27 and obtains a pulse signal (input pulse) amplified by the amplifier 26 from the signal terminal 27 and performs various calculations and data output. When the radiation is counted at different timings using the first measuring device 11p and the second measuring device 11s individually, the data processing device 90 may be switched and connected to each signal terminal 27. A general-purpose computer device can be used as the data processing device 90. The data processing device 90 includes a storage device (not shown), a control device (CPU), and input / output interface equipment.

The data processing device 90 includes a wave height analysis unit 92, a calculation unit 94, and an output unit 96. The pulse height analysis unit 92 detects and counts the maximum energy of the input pulse to generate a radiation spectrum. The pulse height analysis unit 92 can be a multi-channel analyzer that divides and counts the pulse height of an input pulse into a plurality of channels. The computing unit 94 calculates the radioactivity surface density (unit: Bq / cm ² ) and radioactivity (unit: Bq) based on the generated radiation spectrum. The arithmetic unit 94 is realized by a control device (CPU) of a computer device that constitutes the data processing device 90. The output unit 96 is means for outputting the calculated result to a display or the like.

(About collimator)
The collimators 40p and 40s are devices that are mounted in front of the detection element 20 and limit the incident angle of incident radiation to a predetermined range.

  FIG. 2A is an explanatory diagram showing the radiation R shielded by the collimator 40p and the radiation Rp incident on the detection element 20p. The collimator 40p may be referred to as a parallel collimator. FIG. 2B is an explanatory diagram showing the radiation R shielded by the collimator 40s and the radiation Rs incident on the detection element 20s. The collimator 40s may be referred to as a slant collimator. In FIG. 2A and FIG. 2B, the shield 30 is not shown.

  As compared with FIGS. 2A and 2B, the depth direction of the opening 41 of the collimator 40p is orthogonal to the detection surface 22 of the detection element 20p, whereas the opening 41 of the collimator 40s has a depth direction. The depth direction is inclined non-perpendicular to the detection surface 22 of the detection element 20s.

  As described above, in the measurement object 100 of this embodiment, the collimating direction of the sensing element 20 can be changed or selected. One collimating direction (collimating direction of the collimator 40p) coincides with the detecting direction of the detecting element 20, and the other collimating direction (collimating direction of the collimator 40s) is inclined with respect to the detecting direction of the detecting element 20. Yes.

  However, as long as the collimating directions of the detecting elements 20p and 20s are different from each other, the measuring apparatus 10 of the present embodiment does not need to coincide with the detecting direction (directing direction) of the detecting element. Instead of this embodiment, the collimating directions of the collimators 40p and 40s may be inclined at different angles with respect to the detection elements 20p and 20s.

  The collimator 40p (parallel collimator) has a cylindrical shape concentric with the detection surface 22, and has a plurality of concentric annular openings 41. The partition walls 42 that partition adjacent openings 41 have a surface density capable of shielding characteristic X-rays. Specifically, the partition wall 42 can be made of stainless steel having a thickness of 0.25 mm or more. The partition walls 42 are arranged in multiple concentric circles and have a short cylindrical shape with different opening diameters. A mounting portion 47 for mounting on the housing 12 of the first measuring instrument 11p is provided around the base end side of the collimator 40p.

  The height dimension of the partition wall 42 in the collimator 40p is equal to the interval between the adjacent partition walls 42, and can be, for example, 5 mm or more and 20 mm or less. The height dimension of the partition wall 42 is the length of the partition wall 42 in the direction of the directional axis of the detection element 20 (the normal direction of the detection surface 22). Thereby, the partition wall 42 of the collimator 40p passes the characteristic X-rays traveling in parallel with the partition wall 42 or along the partition wall 42 at a shallow intersection angle less than a predetermined value. Then, the characteristic X-rays traveling at a deep intersection angle greater than or equal to a predetermined distance with respect to the partition wall 42 are shielded. As a result, radiation (characteristic X-rays) R incident at an incident angle θ of a predetermined angle or more (60 degrees or more in the present embodiment) is shielded. In the present embodiment, radiation R having an incident angle of 45 degrees or more traveling in a two-dimensional plane passing through the axis of the collimator 40p, and incident angle of approximately 60 degrees or more traveling in a three-dimensional space inside the collimator 40p in an arbitrary direction. All of the radiation R is shielded. The incident angle of the radiation R such as a characteristic X-ray is an angle formed by the direction of the directional axis of the detection element 20 and the traveling direction of the radiation R, and the directional axis direction of the detection element 20 is zero degrees. The average incident angle θp of the radiation Rp incident through the collimator 40p is different from the average incident angle θs of the radiation Rs incident through the collimator 40s.

  By providing the collimator 40p, the characteristic X-ray incident on the detection surface 22 is collimated so that the incident angle θ is not less than 0 degrees and not more than 60 degrees. When the average incident angle θp of the characteristic X-ray passing through the opening 41 of the collimator 40p was calculated by the EGS (Electron Gamma Shower) method which is a Monte Carlo simulation method, it was about 30 degrees.

  The average incident angle θs of the collimator 40s (slant collimator) is larger than the average incident angle θp of the collimator 40p (parallel collimator). In the collimator 40s, the partition wall 42 is inclined in a funnel shape (conical frustum shape) so as to increase in diameter toward the tip side. In the center of the collimator 40s, a truncated cone-shaped shielding region 44 is provided. The shielding region 44 is made of a metal material such as copper, and the characteristic X-rays that collide with the shielding region 44 are shielded.

  In the collimator 40s of the present embodiment, the inclination angle formed by the extending direction of the partition wall 42 and the direction of the pointing axis of the detection element 20s is 60 degrees. That is, when the collimator 40s is directly opposed to the surface 110 (see FIG. 1) of the measurement object 100, the partition wall 42 is inclined by 30 degrees with respect to the surface 110. Of the characteristic X-rays flying from the arbitrary direction to the opening 41 of the collimator 40s, the average incident angle θs of the characteristic X-rays that passed through the collimator 40s was calculated by the EGS method, which was about 60 degrees.

The collimator 40s (slant collimator) of this embodiment is used in a radiation measurement method described later.
The collimator 40s includes a mounting portion 47 and a tilted opening 41s that are mounted on a radiation measuring apparatus (second measuring device 11s) including a detection element 20s that detects the radiation Rs. The inclined opening 41s opens in a direction inclined with respect to the detection direction of the detection element 20s in a state where the mounting portion 47 is mounted on the second measuring instrument 11s. The collimator 40 s shields radiation R having an incident angle θ with respect to the detection direction of the detection element 20 s within a predetermined angle (30 degrees or less in this embodiment) among the radiation incident on the inclined opening 41 s.

  The pitch (inter-wall distance) between the adjacent partition walls 42 in the collimator 40s is smaller than the pitch (inter-wall distance) between the adjacent partition walls 42 in the collimator 40p. In the collimator 40s, the lower end of the partition wall 42 positioned on the inner diameter side is positioned on the outer diameter side of the upper end of the partition wall 42 adjacent to the outer diameter side. Similarly, the outer edge of the lower end of the shielding region 44 is located on the outer diameter side of the upper end of the innermost peripheral partition wall 42. Thereby, the detection surface 22 is not exposed in the lower surface view (front end view) of the collimator 40s. Thereby, the collimator 40s of the present embodiment shields the radiation R incident on the collimator 40s at a small incident angle θ of a predetermined angle (for example, 45 degrees) or less.

  As described above, the collimators 40p and 40s may be detachably attached to the first measuring instrument 11p and the second measuring instrument 11s, respectively, or the collimators 40p and 40s with respect to one measuring instrument 11. May be used interchangeably. In addition, the function of the collimators 40p and 40s may be realized by a single collimator by making the angle of the partition wall 42 variable. That is, instead of the present embodiment, the measuring object 100 (measuring instrument 11) may include a collimator that is detachably attached to the sensing element 20 and whose collimating direction is variable.

  Although the specific structure of such a collimator is not particularly limited, as an example, a drive mechanism (not shown) that varies the extending direction of the partition wall 42 with respect to the direction of the directional axis of the detection element 20 may be provided. This drive mechanism includes a cylindrical first aspect in which the generatrix direction of the cylindrical partition wall 42 coincides with the direction of the directional axis of the detection element 20, and the truncated cone in which the generatrix direction is inclined with respect to the directional axis direction of the detection element 20. The curved direction of the partition wall 42 is changed commutatively to the second shape. Thereby, a collimator functions as a collimator 40p (parallel collimator) in the first mode, and functions as a collimator 40s (slant collimator) in the second mode. Therefore, the function of the measuring object 100 of the present embodiment described above can be realized by a single collimator and measuring instrument 11.

  That is, the collimator includes a mounting portion that is mounted on a radiation measuring apparatus (measuring instrument) that includes a detection element that detects radiation, a partition that partitions a plurality of openings, and the shape of the partition is the same as the first aspect. And a drive mechanism that can be changed in two modes. The partition wall has a shape including a curved surface, and the generatrix direction of the curved surface is different between the first mode and the second mode. In particular, in the first aspect, the bus-line direction of the partition wall coincides with the directing axis direction of the detection element, and in the second aspect, the bus-line direction of the partition wall is preferably inclined with respect to the directing axis direction of the detection element.

  A lid member 46 for shielding beta rays, internal conversion electrons, and Auger electrons is provided on the front end surfaces of the openings 41 of the collimators 40p and 40s. Internally converted electrons are electrons that are emitted instead of gamma rays when a nucleus in an excited state transitions to the ground state, and its energy is smaller than that of main gamma rays. Auger electrons are electrons emitted instead of characteristic X-rays when electrons transition from the outer shell to the inner shell of an atom in an excited state. Since the transmission power of these electrons is smaller than that of the characteristic X-ray, by providing the lid member 46, it is possible to transmit the characteristic X-ray and shield these electrons. As the lid member 46, a resin material of about 1 mm or more and 10 mm or less can be used. The resin material is not particularly limited, and a polyester resin such as polyethylene terephthalate or an acrylic resin can be used.

  FIG. 3 is a schematic diagram showing radiation Rp and Rs incident on the detection elements 20p and 20s. The radiation Rp is a characteristic X-ray that has passed through the parallel collimator with an average incident angle θp, and the radiation Rs is a characteristic X-ray that has passed through the slant collimator with an average incident angle θs.

FIG. 3 illustrates a state in which the radioactive substance 102 is uniformly distributed in a planar shape in the deep portion 112 at a depth distance D from the soil surface 110 of the measurement target 100.
The passage distance of the radiation Rp from the deep part 112 to the surface 110 is the first length L1, and the relationship with the depth distance D is expressed by the following equation (1).
[Equation 1]
L1 = D / cos θp (1)
Similarly, the passage distance of the radiation Rs from the deep portion 112 to the surface 110 is the second length L2, and the relationship with the depth distance D is expressed by the following equation (2).
[Equation 2]
L2 = D / cos θs (2)

The intensity I of radiation such as a characteristic X-ray attenuates exponentially as shown in the following formula (3) according to the distance L through which the radiation passes through the medium. I ₀ is the initial intensity and is the true radioactivity of the radioactive material in the deep part 112. η is an attenuation coefficient determined by the radiation and the medium.
[Equation 3]
I = I ₀ · exp (−η · L) (3)

From the expressions (1) to (3), the intensity Ip of the radiation Rp and the intensity Is of the radiation Rs are expressed by the following expressions (4) and (5), respectively.
[Equation 4]
Ip = I ₀ · exp (−η · D / cos θp) (4)
[Equation 5]
Is = I ₀ · exp (−η · D / cos θs) (5)

Taking the ratio between Ip and Is, the following equation (6) is obtained.
[Equation 6]
Is / Ip = exp {−η · (1 / cos θs−1 / cos θp) · D} (6)
In Expression (6), the attenuation coefficients η, cos θs, and cos θp are known values. Therefore, by determining the ratio between Ip and Is, the depth distance D where the radioactive substance 102 exists can be calculated even if the initial intensity I ₀ is unknown. The ratio between Ip and Is may be Is / Ip as in Equation (6), or may be Ip / Is.

Then, the initial intensity I of the radioactive substance 102 is substituted by substituting the measured intensity Ip or intensity Is and the depth distance D calculated by the expression (6) into any of the expressions (4) to (6). ₀ , that is, the true radioactivity in the deep portion 112 can be calculated. The unit of the depth distance D here is a surface density depth (g / cm ² ) as will be described later. Therefore, when the physical depth of the radioactive substance 102 is obtained, the surface density depth may be divided by the density (g / cm ³ ) of the measurement object 100.

Further, the depth distance D and the true radioactivity I ₀ calculated according to the present embodiment are not limited to the state in which the radioactive substance 102 is distributed in a flat shape in the uniform deep portion 112 as shown in FIG. When the radioactive substance 102 is evenly distributed inside the measurement object 100, or when the surface 110 is distributed exponentially in the depth direction with the maximum value as the surface 110, the depth is set as an effective value corresponding to each distribution. The distance D and the true radioactivity I ₀ can be obtained.

Hereinafter, a method of calculating the radioactivity characteristics in the deep portion 112 of the measurement object 100 using the measurement apparatus 10 of the present embodiment (hereinafter, may be referred to as the present method) will be described. As the radioactivity characteristics, in addition to the true radioactivity I ₀ in the deep part 112 of the measurement object 100, the depth position (physical depth) of the radioactive substance 102, the passing distance (first length) from the radioactive substance 102 to the surface 110. L1, the second length L2), and the like, but are not limited thereto.

  This method is a method for measuring the radiation emitted by the radioactive substance 102 existing in the deeper part 112 than the surface 110 of the measurement object 100. In this method, the first measurement for measuring the radiation Rp radiated from the deep part 112 and having a first distance L1 from the deep part 112 to the surface 110, and the deep part 112 radiated from the deep part 112. A second measurement is performed to measure the radiation Rs having a second length L2 in which the passing distance to the surface 110 is longer than the first length L1. And this method calculates the radioactivity characteristic in the deep part 112 based on the ratio of the measurement result measured by 1st measurement, and the measurement result measured by 2nd measurement.

  Fig.4 (a) is a schematic diagram which shows the structure of the 1st measuring device 11p used for the 1st Example. FIG. 4B is a schematic diagram showing the configuration of the second measuring instrument 11s used in the first embodiment.

  In the first embodiment, a standard surface ray source 120 having a known radioactivity is placed on the base 140, and a shielding plate 130 similar to a soil component is stacked one by one on the standard surface ray. The depth distance D from the source 120 to the surface 110 is varied. The radiation spectrum was generated by counting the radiation Rp and the radiation Rs with the first measuring device 11p and the second measuring device 11s while changing the number of the shielding plates 130. As described above, the average incident angle θs of the radiation Rs passing through the collimator 40s (slant collimator) is larger than the average incident angle θp of the radiation Rp passing through the collimator 40p (parallel collimator). The first length L1, which is the passing distance from the radiation Rp counted by the first measuring instrument 11p to the surface 110 of the shielding plate 130 after being emitted from the standard surface ray source 120, is expressed by the above equation (1). Is done. Similarly, the second length L2, which is the passing distance from the radiation Rs counted by the second measuring instrument 11s from the standard surface ray source 120 to the surface 110 of the shielding plate 130, is expressed by the above equation (2). ). The second length L2 is larger than the first length L1.

  That is, this method is a radiation measurement method performed using collimated detection elements 20p and 20s that detect photons, and the second measurement is performed with respect to the average incident angle θp of the photons incident on the detection element 20p in the first measurement. The average incident angle θs at is increased.

  In the first measurement, the detection element 20p is directly opposed to the surface 110 of the shielding plate 130, and the detection direction of the detection element 20p is matched with the collimating direction. Thereby, the radiation Rp enters the detection element 20p from directly below, and the first length L1 can be shortened. In other words, since the difference between the second length L2 and the first length L1 can be increased, it is included in the ratio (Is / Ip) between the measurement result of the first measurement and the measurement result of the second measurement described later. Error can be reduced.

As the standard plane source 120, a beta plane surface emission rate standard plane source provided by the Japan Isotope Association is used. A polyimide film with a thickness of 12.5 μm, a polyethylene film with a thickness of 10 μm, and a thickness of 0. A protective film of 3 mm polystyrene was laminated.
A polystyrene plate having a thickness of 3 mm was used for the lid member 46 covering each of the openings 41 of the collimators 40p and 40s.

  As the base 140, a lead plate having a thickness of 10 mm was used. As a result, the back-scattered gamma rays emitted from the standard plane source 120 are shielded. NaI (Tl) scintillators with a thickness of 0.5 mm were used for the sensing elements 20p and 20s.

For the shielding plate 130, (1) a glass plate obtained by forming soda glass (density 2.5 g / cm ³ ) mainly composed of silica alkali oxide into a plate shape having a thickness of 0.7 mm; and (2) alumina. And a mullite plate formed by molding mullite (density 1.4 g / cm ³ ), which is a compound of silica and silica, into a plate shape having a thickness of 1.0 mm. One glass plate and mullite plate were used, or a plurality of the same type of plates were laminated. Regarding the characteristic X-ray of barium, the attenuation coefficient η of the glass plate is 0.206 / mm, and the half thickness is 3.4 mm. Similarly, the attenuation coefficient η of the mullite plate is 0.115 / mm, and the half-thickness is 6.0 mm.

  Using the above measurement apparatus 10, the first measurement for counting the radiation Rp with the first measuring device 11p and the second measurement for counting the radiation Rs with the second measuring device 11s were performed. 4 (a) and 4 (b) illustrate the state where the first measuring instrument 11p and the second measuring instrument 11s and the surface 110 of the shielding plate 130 are separated from each other for convenience. In the measurement, both were brought into close contact with each other.

  FIG. 5 is a radiation spectrum SP1 showing the measurement result of the second measurement. The horizontal axis represents photon energy, and the vertical axis represents the count value. The measurement result of the first measurement is omitted. FIG. 6 is a graph showing a state in which the radiation spectrum SP1 of the second measurement is fitted with an approximate function. In this example, characteristic X-rays (32.1 keV, 36.5 keV) of barium originating from radioactive cesium were counted as the radiation Rp and Rs. FIG. 6 is an enlarged view of the vicinity of the wavelength of this characteristic X-ray.

  As shown in FIG. 6, a characteristic X-ray peak P1 originating from radioactive cesium was observed at a position of about 33 keV. An approximate function of the radiation spectrum SP1 was obtained using a function fitting method for a spectral region having the lower limit and the upper limit of the minimum points adjacent to both sides of the characteristic X-ray peak P1. As an approximate function, a function including a linear term, an exponential term, and a Gaussian function was used, and the radiation spectrum SP1 was approximated by a nonlinear least square method. Gaussian functions G1 and G2 were obtained from the approximate function, and an effective count rate was calculated by subtracting the baseline from the characteristic X-ray peak P1 from these areas.

  FIG. 7 is a graph showing the relationship between the thickness of the shielding plate 130 and the characteristic X-ray count rate. The horizontal axis represents the thickness (mm) of the shielding plate 130, and the vertical axis represents the counting rate of radiation (characteristic X-rays) Rp and Rs. CR1 is a counting rate of the radiation Rp indicating the result of the first measurement when a glass plate is used as the shielding plate 130. CR2 is a counting rate of the radiation Rs indicating the result of the second measurement when a glass plate is used as the shielding plate 130. CR3 is a counting rate of the radiation Rp indicating the result of the first measurement when the mullite plate is used as the shielding plate 130. As shown in FIG. 7, when the physical thickness of the shielding plate 130 is set on the horizontal axis, the result (CR1) of counting the radiation Rp that has passed through the glass plate with the first measuring instrument 11p (see FIG. 4) and The slope (decay tendency) of the counting rate was different from the result of counting the radiation Rp that passed through the mullite plate (CR3). The result of counting the radiation Rs that passed through the glass plate with the second measuring instrument 11s (CR2) and the result of counting the radiation Rs that passed through the mullite plate (not shown) were the same.

  That is, the soil is composed of components similar to glass plates or mullite plates, and the components are variously different for each region. As shown in FIG. 7, the slope of the count rate for each component of the soil (shielding plate 130) ( If the attenuation tendency is different, the depth distance D (physical thickness) cannot be calculated unless the attenuation coefficient η in the above equation (6) is specified in advance for each area where the attenuation coefficient η is measured.

On the other hand, FIG. 8 is a replot of FIG. 7 with the horizontal axis representing the surface density (g / mm ² ) of the shielding plate 130 and the vertical axis representing the radiation (characteristic X-ray) Rp, Rs count rate. That is, FIG. 8 is a graph showing the relationship between the surface density of the shielding plate 130 and the characteristic X-ray count rate. FIG. 8 also shows a graph showing the relationship between the surface density (horizontal axis) of the shielding plate 130 and the ratio (vertical axis) of the measurement results of the first measurement and the second measurement.

  CR1a to CR3a correspond to CR1 to CR3 in FIG. 7, respectively. As shown in FIG. 8, by setting the surface density of the shielding plate 130 on the horizontal axis, the counting result (CR1a) of the first measuring instrument 11p when the shielding plate 130 is a glass plate, and the mullite plate Was completely consistent with the counting result (CR3a). Similarly, the counting result (CR2a) of the second measuring instrument 11s when the shielding plate 130 is a glass plate and the counting result (not shown) when the shielding plate 130 is a mullite plate almost completely coincided.

From the above, by setting the horizontal axis as the surface density of the shielding plate 130, the slope (decay tendency) of the counting rate does not change even if the components of the shielding plate 130 (soil) differ to some extent. The depth distance D can be calculated without specifying.
CR4 is the ratio (Is / Ip) between the measurement result of the first measurement and the measurement result of the second measurement. Specifically, CR2a is divided by CR1a. This CR4 corresponds to the right side of the above equation (6). However, η in the equation is an attenuation rate per area density (cm ² / g), and D is an area density thickness (g / cm ² ). 8 is a logarithm, and the slope of CR4 corresponds to −η · (1 / cos θs−1 / cos θp).
Therefore, even when the surface density thickness (D) of the shielding plate 130 is unknown, the ratio (Is / Ip) between the measurement result of the first measurement and the measurement result of the second measurement is calculated and applied to the CR4 graph. By doing so, the surface density thickness (D) of the shielding plate 130 can be obtained. Since the CR4 graph does not depend on the components of the shielding plate 130 (soil) as described above, the above relationship is established even in the field of contaminated sites that are radioactively contaminated.

  FIG. 9 is a diagram showing the results of the second example performed using contaminated soil, and shows the relationship between the surface density depth of the measurement object (soil) and the ratio of the measurement results of the first measurement and the second measurement. It is a graph.

  When performing the first measurement and the second measurement in the field of the contamination site, it is preferable to suppress the influence of the environmental radiation flying from the periphery of the measurement apparatus 10 to the detection element 20. Thereby, the radiation Rp having the first length L1 and the radiation Rs having the second length L2 radiated from the deep part 112 and reaching the surface 110 can be accurately discriminated from the environmental radiation and counted. For this reason, the side peripheral portions 32p and 32s of the shield 30 are attached to at least the side periphery of the detection elements 20p and 20s to shield the scattered gamma rays and characteristic X-rays included in the environmental radiation.

  In the first measurement and the second measurement, the characteristic X-ray of the radioactive substance 102 was measured. Thereby, compared with the case where the main gamma ray is measured, the surface density of the shield 30 (side peripheral portions 32p, 32s) can be reduced to about several mm in terms of lead, and the weight of the measuring device 10 can be reduced. Figured.

  That is, in the first measurement and the second measurement, the collimating direction is shielded from the scattered gamma rays and the characteristic X-rays that are the scattered rays of the gamma rays flying from the direction different from the collimating direction of the sensing elements 20p and 20s. From the characteristic X-rays, the scattered gamma rays and the gamma rays flying to the sensing elements 20p and 20s, the characteristic X-rays were discriminated and measured.

The CR4a shown in FIG. 9 is obtained by displaying the CR4 of FIG. 8 on the normal scale on both the vertical axis and the horizontal axis. The measurement result Ip of the first measurement using the first measuring device 11p shown in FIG. 1 was 11.3 cps, and the measurement result Is of the second measurement using the second measuring device 11s was 6.3 cps. Thereby, the ratio (Is / Ip) of the measurement results was 0.48, and the measurement error was ± 0.01. By reading the intersection of Is / Ip = 0.48 and CR4a, the effective surface density thickness (surface density depth) D of the radioactive substance in this measurement object (soil) is 0.13 ± 0.04 [g / cm ² ].
Therefore, by dividing the effective surface density thickness (surface density depth) D by the soil density (for example, 1 g / cm ³ ), the physical depth of this radioactive substance is 0.13 ± 0.04 cm = 1.3 ± 0. It was determined to be 4 mm. As described above, it was found that the depth position of the radioactive substance existing deeper than the surface can be measured easily and accurately by using the measuring apparatus 10 of the present embodiment.

  As described above, according to the present method, the depth distance D from the surface 110 to the deep part 112 can be calculated as the radioactivity characteristic of the measurement object 100.

Further, the radioactivity of the radioactive substance 102 in the deep part 112 can be calculated as the radioactivity characteristic of the measurement object 100. Specifically, the calculated surface density depth (D) and the attenuation rate per surface density (η) [cm ² / g] are applied to the right side of the above equation (4) or (5). By applying the measurement result Ip or Is to the left side, the true radioactivity I ₀ of the radioactive substance in the deep part can be calculated.

A function or table representing the CR4a may be stored as conversion information in a storage unit (not shown) of the data processing device 90 shown in FIG. As a result, the calculation unit 94 of the data processing device 90 refers to the conversion information described above, only by performing the first measurement and the second measurement using the measuring device 10 and acquiring the measurement results Ip and Is. The surface density depth (D) can be calculated. The calculation unit 94 may calculate the physical depth of the radioactive substance by multiplying the surface density depth (D) by the numerical value of the soil density of the measurement target 100, or the radioactive substance according to the formula (4) or (5). it may calculate the true radioactivity I _0. The true radioactivity I ₀ can be calculated in units of radioactivity surface density [Bq / cm ² ] or radioactivity [Bq].

  The present invention is not limited to the above-described embodiment, and includes various modifications and improvements as long as the object of the present invention is achieved.

The above embodiment includes the following technical idea.
(1) A method for measuring radiation radiated from a radioactive substance existing deeper than a surface to be measured, the radiation radiated from the deep part and having a first length of passing distance from the deep part to the surface And a second measurement that measures radiation that is radiated from the deep part and has a second length that is longer than the first length by the passage distance from the deep part to the surface, and A radiation measurement method, wherein the radioactivity characteristic in the deep part is calculated based on a ratio between a measurement result measured in the first measurement and a measurement result measured in the second measurement.
(2) The radiation measurement method according to (1), wherein a depth distance from the surface to the deep part is calculated as the radioactivity characteristic.
(3) The radiation measuring method according to (1), wherein the radioactivity of the radioactive substance in the deep part is calculated as the radioactivity characteristic.
(4) The radiation measurement method according to any one of (1) to (3), wherein the radiation measurement method is performed using a collimated detection element that detects photons, and is incident on the detection element in the first measurement. A radiation measurement method, wherein the average incident angle in the second measurement is made larger than the average incident angle of the photons.
(5) The radiation measurement method according to (4), wherein in the first measurement, the detection element is directly opposed to the surface, and a detection direction of the detection element is matched with a collimating direction.
(6) The radiation measurement method according to (4) or (5), wherein a characteristic X-ray of the radioactive substance is measured in the first measurement and the second measurement.
(7) In the first measurement and the second measurement, the collimating direction in a state in which scattered gamma rays and characteristic X-rays that are scattered gamma rays flying to the sensing element from directions different from the collimating direction of the sensing element are shielded The radiation measurement method according to (6), wherein the characteristic X-rays flying from the light to the detection element, the scattered gamma rays, and the gamma rays are discriminated and measured.
(8) A collimator used in the radiation measurement method according to any one of (1) to (7) above, a mounting unit that is mounted on a radiation measurement device including a detection element that detects radiation, An inclination opening opening in a direction inclined with respect to the detection direction of the detection element in a state where the attachment part is attached to the radiation measuring apparatus, and the detection of the radiation incident on the inclination opening A collimator that shields the radiation having an average incident angle with respect to a direction equal to or less than a predetermined value.
(9) A directional measuring device that includes a collimated sensing element that detects photons, and that measures radiation emitted by a radioactive substance that exists deeper than the surface of the measurement target, the collimating direction of the sensing element being Variable or selectable, a first measurement that measures radiation radiated from the deep part and having a first length passing distance from the deep part to the surface; and radiated from the deep part to the surface from the deep part And a second measurement that measures radiation having a second length that is longer than the first length.
(10) The radiation measuring apparatus according to (9), including a plurality of collimators that are detachably attached to the detection element and have different collimating directions.
(11) The radiation measuring apparatus according to (9), further including a collimator that is detachably attached to the detection element and has a variable collimating direction.
(12) One of the collimating directions is coincident with the detecting direction of the detecting element, and the other collimating direction is inclined with respect to the detecting direction of the detecting element. The radiation measuring apparatus according to (11).

DESCRIPTION OF SYMBOLS 10 Measuring apparatus 11 Measuring instrument 11p 1st measuring instrument 11s 2nd measuring instrument 12 Housing 20, 20p, 20s Detection element 22 Detection surface 24 Photoelectric conversion apparatus 26 Amplifier 27 Signal terminal 28 Power supply terminal 30 Shielding body 32p, 32s Side circumference 34 Base end portion 36 Top surface portion 40p, 40s Collimator 41 Opening 41s Inclined opening 42 Bulkhead 44 Shielding region 46 Lid member 47 Mounting portion 70 Base 90 Data processing device 92 Wave height analysis portion 94 Calculation portion 96 Output portion 100 Measurement object 102 Radioactive substance 110 Surface 112 Deep portion 120 Standard plane source 130 Shield plate 140 Base θ Incident angle θp Average incident angle θs Average incident angle η Attenuation rate (attenuation coefficient)
D Depth distance (surface density depth)
I, Ip, Is Intensity I0 Initial intensity (true radioactivity)
L1 1st length L2 2nd length P1 Characteristic X-ray peak R, Rp, Rs Radiation SP1 Radiation spectrum

Claims (12)

A method for measuring radiation emitted by a radioactive substance existing deeper than the surface of a measurement object,
A first measurement that measures radiation radiated from the deep part and having a first length of a passing distance from the deep part to the surface;
Performing a second measurement of radiation radiated from the deep part and measuring a radiation having a second length that is longer than the first length by a distance from the deep part to the surface;
A radiation measurement method, wherein the radioactivity characteristic in the deep part is calculated based on a ratio between a measurement result measured in the first measurement and a measurement result measured in the second measurement.   The radiation measurement method according to claim 1, wherein a depth distance from the surface to the deep part is calculated as the radioactivity characteristic.   The radiation measurement method according to claim 1, wherein the radioactivity of the radioactive substance in the deep part is calculated as the radioactivity characteristic. The radiation measurement method according to any one of claims 1 to 3, wherein the radiation measurement method is performed using a collimated sensing element that detects photons.
The radiation measurement method characterized in that the average incident angle in the second measurement is made larger than the average incident angle of the photons incident on the sensing element in the first measurement.   The radiation measurement method according to claim 4, wherein in the first measurement, the detection element is directly opposed to the surface, and a detection direction of the detection element is matched with a collimating direction.   6. The radiation measurement method according to claim 4, wherein a characteristic X-ray of the radioactive substance is measured in the first measurement and the second measurement.   In the first measurement and the second measurement, the detection from the collimation direction in a state where the scattered gamma rays and the characteristic X-rays, which are scattered gamma rays flying to the detection element from directions different from the collimation direction of the detection element, are shielded. The radiation measuring method according to claim 6, wherein the characteristic X-rays that come to the element, the scattered gamma rays, and the gamma rays are discriminated and measured. A collimator used in the radiation measurement method according to claim 1,
A mounting portion mounted on a radiation measuring device including a detection element for detecting radiation, and an inclination opening in a direction inclined with respect to the detection direction of the detection element in a state where the mounting portion is mounted on the radiation measuring device. An opening, and
A collimator for shielding the radiation having an average incident angle with respect to the detection direction out of the radiation incident on the inclined opening. A directional measuring device that includes a collimated sensing element that detects photons, and that measures radiation emitted by radioactive materials that exist deeper than the surface of the measurement object,
The collimating direction of the sensing element is variable or selectable, and a first measurement for measuring radiation that is radiated from the deep part and has a first length from the deep part to the surface; and radiated from the deep part. And a second measurement that measures radiation having a second length that is longer than the first length by a passing distance from the deep part to the surface.   The radiation measurement apparatus according to claim 9, further comprising a plurality of collimators that are detachably attached to the detection element and have different collimating directions.   The radiation measuring apparatus according to claim 9, further comprising a collimator that is detachably attached to the detection element and has a variable collimating direction.   The one collimating direction coincides with the detection direction of the detection element, and the other collimation direction is inclined with respect to the detection direction of the detection element. Radiation measurement device.

Images