Scintillator and radiation measuring device

Abstract

To provide a scintillator capable of obtaining high sensitivity and light emission quantity.SOLUTION: A scintillator is constituted of a eutectic body consisting of a plurality of crystal phases including at least a first crystal phase 101 containing Li and a second crystal phase 102 emitting radiation with radiation excitation. Moreover, each of the plurality of crystal phases constituting the scintillator has a refractive index difference of 0.04 or less. This scintillator functions as a neutron scintillator which generates scintillation light, for example, by the incidence of neutrons.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a scintillator and a radiation measuring device. [Background technology]

[0002] Neutron detectors (measuring devices) have a wide range of application areas, including crystal structure analysis of organic and inorganic substances, medical technology such as boron neutron capture therapy using neutron beams, neutron beam detection at high-energy synchrotron radiation facilities, non-destructive testing, and security fields such as cargo inspection, etc. Furthermore, with the development of neutron utilization technology, there is a demand for neutron detectors with higher sensitivity.

[0003] For example, Patent Document 1 describes Ce-doped Cs 2 LiYCl 6 A single crystal of the compound is disclosed as a neutron scintillator having a light emission yield of 73,000 photons per neutron.

[0004] Furthermore, for example, Patent Document 2 and Non-Patent Document 1 disclose a eutectic consisting of lithium fluoride crystals, calcium fluoride crystals, and strontium fluoride, which contains Ce or Eu as a luminescent center element, and in which calcium fluoride and lithium fluoride emit light when excited by radiation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 8,969,824 [Patent Document 2] JP 2011-232305 A [Non-patent literature]

[0006] [Non-Patent Document 1] T. Yanagida et al., "Scintillation properties of LiF-SrF2 and LiF-CaF2 eutectic", Journal of Luminescence, vol. 144, pp. 212-216, 2013. Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the technology of Patent Document 1, although the single crystal has high transparency and a high amount of light emission, the chemical composition of the compound single crystal is limited, so the Li content cannot be increased. 2 LiYCl 6 The Li molar content in the alloy is as low as 10%, which results in low sensitivity to neutron radiation.

[0008] On the other hand, in the technology according to Patent Document 2 and Non-Patent Document 1, a eutectic scintillator is formed in which layered lithium fluoride crystals, layered calcium fluoride crystals, and strontium fluoride crystals are alternately stacked, and the calcium fluoride crystals and strontium fluoride crystals emit light when excited by radiation. Here, the difference in refractive index between the lithium fluoride crystals and the layered calcium fluoride and strontium fluoride is as large as 0.04 or more at the emission wavelength. Therefore, in this technology, the light emitted by radiation excitation is scattered and absorbed between each crystal phase, so the transmittance is reduced, and the scintillation light is attenuated in the scintillator before reaching the light receiving element, resulting in a problem of reduced light emission.

[0009] As described above, the conventional techniques have the problem that high sensitivity and light emission amount cannot be obtained.

[0010] The present invention has been made to solve the above problems, and has an object to provide a scintillator which can provide high sensitivity and a high amount of light emission. [Means for solving the problem]

[0011] The scintillator according to the present invention is composed of a eutectic crystal composed of a plurality of crystal phases including a first crystal phase containing Li and a second crystal phase that emits light by radiation excitation, and each of the plurality of crystal phases has a refractive index difference of 0.04 or less from each other.

[0012] In one configuration example of the above scintillator, the second crystal phase is composed of at least one of Pr, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Dy, Er, Tm, Yb, Tl, Pb, Bi, Ag, Ti, Cr as a luminescence center Original and contains 0.001 mol% or more of the element with respect to the total amount of the second crystal phase.

[0013] In one configuration example of the above scintillator, the first crystal phase has the chemical formula A x B y X x+2y (0 < x < 1, 0 < y ≤ 1), and contains a halide represented by the formula, A is an element containing at least one of Li, Na, K, Rb, Cs, B is an element containing at least one of Be, Mg, Ca, Sr, Ba, and X is an element containing at least one of F, Cl, Br, I.

[0014] In one configuration example of the above scintillator, the first crystal phase contains a halide represented by the chemical formula LiX, and X is an element containing at least one of F, Cl, Br, I.

[0015] The radiation measurement device according to the present invention includes any of the above-described scintillators and a light receiving element that receives the scintillation light emitted by the scintillator.

Effects of the Invention

[0016] As described above, according to the present invention, the first crystal phase of the eutectic crystal constituting the scintillator contains Li, and the refractive index difference between each of the plurality of crystal phases constituting the eutectic crystal is 0.04 or less, so that a scintillator with high sensitivity and emission amount can be provided. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing the structure of a scintillator according to the present invention. [Diagram 2] FIG. 2 is a diagram showing the configuration of the radiation measuring device 200. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a scintillator according to an embodiment of the present invention will be described with reference to FIG. 1. This scintillator is composed of a eutectic consisting of a plurality of crystalline phases including at least a first crystalline phase 101 containing Li and a second crystalline phase 102 that emits light when excited by radiation. The first crystalline phase 101 may be configured to emit light when excited by radiation. The eutectic constituting this scintillator may contain, in addition to the first crystalline phase 101 and the second crystalline phase 102, another crystalline phase containing Li. In addition to the first crystalline phase 101 and the second crystalline phase 102, the eutectic may contain, in addition to the first crystalline phase 101 and the second crystalline phase 102, another crystalline phase that emits light when excited by radiation. The plurality of crystalline phases constituting the scintillator have a mutual refractive index difference of 0.04 or less. The shape of the crystalline phase constituting the eutectic of this scintillator is not limited to a substantially cylindrical shape, an elliptical shape, or a matrix shape, as shown in FIG. 1, and may be composed of various shapes, for example, a three-dimensional lamellar structure including a polygonal shape.

[0019] This scintillator functions as a neutron scintillator that generates scintillation light by the incidence of neutrons, for example. First, when neutrons are incident on the first crystal phase 101 containing Li, the neutrons are converted into the Li 6 It is captured by the Li isotope, and a capture reaction occurs to produce the secondary particles α particles and tritium. The Li contained in the first crystal phase has an excellent linear absorption cross section.

[0020] Next, the secondary particles migrate through the scintillator, which is a eutectic, and reach the second crystal phase 102 that emits light in response to radiation, exciting the second crystal phase 102. Finally, the excited second crystal phase 102 emits scintillation light. Thus, in the scintillator according to the embodiment, the first crystal phase 101 serves as a neutron capture material, and the second crystal phase 102 functions as a phosphor. As described above, the first crystal phase 101 constituting the scintillator contains Li, which has an excellent linear absorption cross section, and therefore this scintillator has high sensitivity to neutrons.

[0021] Furthermore, the scintillator according to the embodiment is characterized in that the difference in refractive index between the plurality of crystal phases constituting the scintillator is 0.04 or less. With this configuration, light generated in the second crystal phase 102 that is incident at an angle that does not satisfy the total reflection condition at the interface with another crystal phase is transmitted without attenuation. As a result, the light transmits between the plurality of crystal phases, spreads within the scintillator, and is finally emitted from the scintillator. As a result, for example, if a light receiving element is disposed near the scintillator, the above-mentioned light is received by the light receiving element.

[0022] The second crystal phase 102 and other crystal phases that emit light when excited by radiation have at least one of Pr, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Dy, Er, Tm, Yb, Tl, Pb, Bi, Ag, Ti, and Cr as a luminescence center. Original It is preferable that the second crystal phase 102 contains 0.001 mol % or more of the element based on the total substance amount.

[0023] When the second crystal phase 102 or another crystal phase that emits light upon excitation with radiation contains Nd, Pr, Ce, Eu, Tm, Tl, or Sm, it exhibits a high-speed fluorescence lifetime of several ns to several hundreds of nsec due to fd transition, and when it contains Nd, Sm, Eu, Gd, Tb, Dy, Ho, Dy, Er, Tm, Yb, or Cr, it exhibits a fluorescence lifetime of several hundred nsec to several μn seconds due to ff transition. Also, when the second crystal phase 102 contains Yb, it may exhibit high-speed emission of approximately several nsec due to charge transfer emission depending on the composition of the host crystal.

[0024] The first crystal phase 101 contains a halide represented by the chemical formula A x B y X x+2y (0 < x < 1, 0 < y ≤ 1), where A is an element containing at least one of Li, Na, K, Rb, and Cs, B is an element containing at least one of Be, Mg, Ca, Sr, and Ba, and X is an element containing at least one of F, Cl, Br, and I. Also, the first crystal phase 101 can contain a halide represented by the chemical formula LiX, where X is an element containing at least one of F, Cl, Br, and I.

[0025] In the first crystal phase 101, the 6 Li isotope ratio of the contained Li element is preferably 20 - 99%. 6 By setting the Li isotope ratio to 20% or more, the probability of the above-described capture reaction increases, and the neutron detection efficiency improves. On the other hand, considering the cost related to isotope enrichment, 6 the Li isotope ratio is preferably 99% or less.

[0026] In order to further improve the above-described neutron beam sensitivity and optical waveguide function of the scintillator according to the embodiment, the Li content is preferably included in an amount of 15 mol% or more, more preferably 25 mol% or more, based on the molar amount of each ion of the scintillator. Also, the refractive index difference between each crystal phase is preferably 0.3 or less, the light emission amount is preferably 15000 photons per neutron, and more preferably 30000 photons per neutron. Also, the refractive index difference between each crystal phase is preferably less than 0.04 at the emission wavelength, more preferably 0.03 or less, and even more preferably 0.02 or less.

[0027] According to the embodiment, the difference in refractive index between the crystal phases of the eutectic constituting the scintillator is small, at 0.04 or less, so that light emitted by radiation excitation diffuses to the surroundings without attenuation. As a result, according to the embodiment, a neutron scintillator having high transparency at the emission wavelength and a high amount of light emission can be obtained. Furthermore, by making the eutectic have the first crystal phase 101 containing Li, the Li content can be increased, and a scintillator having high sensitivity to neutron rays can be obtained. Furthermore, a neutron measurement device using this scintillator can measure neutron rays with high sensitivity.

[0028] Incidentally, in order to obtain a scintillator having the eutectic structure described with reference to Fig. 1, it is preferable to manufacture a scintillator with a roughly eutectic composition. However, it is not necessary to deviate from the eutectic composition, and a range of ±20 mol% of the eutectic composition can be considered as an acceptable range for the eutectic composition ratio.

[0029] The reason for defining the allowable range of the composition described above is that a eutectic having a structure as shown in Fig. 1 can be obtained by solidifying the above materials near the eutectic composition. Outside the allowable range, that is, when the composition ratio deviates from the range of the eutectic composition ±15 mol%, one crystal phase will precipitate first, but if the difference in refractive index between the crystal phases is small, the scintillator light generated in the scintillator reaches the light receiving element with little attenuation, so there is no problem even if crystal phases of irregular shapes and sizes precipitate, and the structure of the eutectic and the shape of the crystal phases can be any shape.

[0030] [Manufacturing of scintillator eutectic] The scintillator eutectic can be manufactured by any method that melts and solidifies the desired material system with the optimal composition. For example, it can be manufactured by a method that grows a crystal from a melt, such as the Czochralski method, the micro-pulling down method, the Bridgman method, the EFG (Edge-defined Film-fed Growth) method, or the Kyropoulos method. It can also be manufactured by the floating zone method.

[0031] In addition, the grain size of the crystal phase of the scintillator and the average value of the period of the nearest neighbor distance between crystal phases depend on the solidification rate, and in particular, the period of the nearest neighbor distance is said to have the following correlation. In other words, if the period is λ and the solidification rate is v, then λ2·v = constant. Therefore, by controlling the solidification rate, it is possible to control the grain size of the crystal phase and the period of the nearest neighbor distance between crystal phases.

[0032] [Use of scintillators] A scintillator having a phase separation structure can be used as a radiation measuring device (detector) for neutrons and the like by combining with a light receiving element. In particular, the scintillator according to the embodiment has a light guide function, and can be applied to a situation where light needs to be guided in a specific direction toward a light receiving element without providing a partition. For example, it can be combined with a light receiving element such as a position sensitive photomultiplier tube, a semiconductor light receiving element array, an image intensifier, or a CCD camera. In these cases, it is possible to adjust the emission wavelength of the scintillator to match the light receiving sensitivity characteristics of the light receiving element by adding other materials or a luminescent center substance to the light emitting phase (second crystal phase 102).

[0033] For example, as shown in FIG. 2, by combining a scintillator 201 with a light receiving element 202 capable of receiving scintillation light emitted by the scintillator 201, it becomes possible to use it as a radiation measuring device 200.

[0034] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Furthermore, not all of the combinations of features described in the examples are necessarily essential to the solution of the present invention.

[0035] [Example] First, as shown in Examples 1 to 8 in Table 1, the combinations of the crystal phases were weighed to obtain the respective composition ratios. A sample in which 1 mol% of europium halide was added to the total substance amount was thoroughly mixed with this mixed powder to prepare a powder. In addition, for lithium halide, 6The raw material used had a Li isotope ratio of 95%.

[0036] Next, the mixture of the above-mentioned raw materials was filled into a quartz tube with an inner diameter of 6 mm, and the inside of the quartz tube was filled with 2.0×10 -4 After evacuation to a pressure of less than 1 Pa, the quartz tube was sealed with a gas burner.

[0037] Next, the raw material mixture in the quartz tube was heated by a heater to melt and solidify. After this heating, the rate at which the temperature of the melt was lowered, i.e., the solidification rate, was 20 mm / hr. Through this temperature lowering operation, the melt was completely solidified, and the eutectic in the example was obtained.

[0038] [Comparative Example] First, the combinations of the crystal phases in Comparative Example 1 and Comparative Example 2 shown in Table 1 were weighed to obtain the respective composition ratios. A powder was prepared by thoroughly mixing this mixed powder with a sample in which 1 mol% of europium fluoride was added to the total substance amount. In addition, for lithium fluoride, 6 The raw material used had a Li isotope ratio of 95%.

[0039] Next, the prepared raw material mixture was filled into a carbon crucible having an inner diameter of 6 mm, and the crucible was placed in a vacuum chamber equipped with a heater. Furthermore, the inside of the vacuum chamber was evacuated to 2.0 × 10 -4 After evacuation to a pressure of less than 1 Pa, argon gas was introduced.

[0040] After the gas replacement operation in the vacuum chamber was performed, the raw material mixture was heated by a heater to melt and solidify. The rate at which the temperature of the melt was lowered after this heating, i.e., the solidification rate, was 20 mm / hr. By this temperature lowering operation, the melt was completely solidified, and the eutectic of the comparative example was obtained.

[0041] Next, the eutectic bodies obtained in Examples 1 to 8 and Comparative Examples 1 and 2 were crushed into powders, and powder X-ray diffraction measurements were performed to identify the crystal phase. The obtained eutectic bodies were cut into pieces with a thickness of 0.1 mm using a wire saw equipped with a diamond wire, and the cut surfaces were mirror-polished to obtain wafers. The transmittance of the obtained wafers was measured. Furthermore, the obtained wafers were irradiated with X-rays, and an emission spectrum was obtained using a spectroscope, and the peak wavelength of the obtained spectrum was determined as the emission wavelength.

[0042] [Fabrication and characterization of neutron detectors] The response characteristics of the neutron scintillator to neutrons were evaluated by the following method. First, the neutron scintillator was attached to the photoelectric surface of a photomultiplier tube (Hamamatsu Photonics, R7600U) on a surface perpendicular to the solidification direction to create a neutron detector (measurement device). The neutron detector was then covered with a black vinyl sheet light-shielding material to prevent outside light from entering the photoelectric surface of the photomultiplier tube, and a neutron detector with a radioactivity of 1MBq was then inserted. 252 Neutrons from Cf were moderated through a neutron moderator made of a 40 mm thick polyethylene block and irradiated.

[0043] To measure the scintillation light emitted from the neutron scintillator, a high voltage of 800V was applied to the photomultiplier tube from the power supply line, and the scintillation light was converted into an electrical signal, which was output from the signal output line. Here, the electrical signal output from the photomultiplier tube was a pulsed signal reflecting the scintillation light, and the pulse height represented the luminous intensity of the scintillation light. The electrical signal output from the photomultiplier tube was shaped and amplified by a shaping amplifier, and then input to a multi-pulse height analyzer for analysis, creating a pulse height distribution spectrum, and the amount of light emitted was calculated by comparing it with Li-glass, the reference material for neutron scintillators.

[0044] Table 1 shows the evaluation results of the eutectic bodies obtained in Examples 1 to 8 and Comparative Examples 1 and 2. In the scintillators of Comparative Examples 1 and 2, the difference in refractive index between the respective crystal phases is 0.04 or more, so the transmittance is low. Furthermore, the amount of emitted light is low, so the performance is reduced when used as a neutron detector (measuring instrument). Generally, neutron detectors use large neutron scintillators with a diameter of more than 1 inch and a thickness of more than 1 inch, so in the scintillators of Comparative Examples 1 and 2, which have low transmittance, the larger the size and thickness of the crystals, the greater the attenuation of light in the scintillator, and the further the amount of emitted light is reduced.

[0045] The eutectic bodies shown in Examples 1 to 8 have a transmittance of 65% or more because the difference in refractive index between the crystal phases is 0.03 or less. Furthermore, the amount of light emitted is high at 35,000 photons or more per neutron, and the molar content of Li is also high at 14% or more, so a neutron detector with excellent sensitivity can be realized.

[0046] [Table 1]

[0047] As described above, according to the present invention, the first crystal phase of the eutectic that constitutes the scintillator contains Li, and the refractive index difference between each of the multiple crystal phases that constitute the eutectic is 0.04 or less, making it possible to provide a scintillator that has high sensitivity and high light emission.

[0048] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0049] 101...first crystal phase, 102...second crystal phase.

Claims

1. The present invention is composed of a eutectic having a plurality of crystalline phases including a first crystalline phase containing Li and a second crystalline phase that emits light when excited by radiation; The refractive index difference between each of the plurality of crystal phases is 0.04 or less, The second crystal phase contains at least one element selected from the group consisting of Pr, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Dy, Er, Tm, Yb, Tl, Pb, Bi, Ag, Ti, and Cr as a luminescence center in an amount of 0.001 mol% or more with respect to the total amount of substance of the second crystal phase; The first crystalline phase contains a halide represented by a chemical formula A x B y X x+2y (0<x<1, 0<y≦1), A is Li; B is an element including at least one of Be, Mg, Ca, Sr, and Ba; X is an element containing at least one of Cl, Br, and I. A scintillator comprising:

2. A eutectic consisting of a plurality of crystalline phases including a first crystalline phase containing Li and a second crystalline phase that emits light upon excitation with radiation; The refractive index difference between each of the plurality of crystal phases is 0.04 or less, The second crystal phase contains at least one element selected from the group consisting of Pr, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Dy, Er, Tm, Yb, Tl, Pb, Bi, Ag, Ti, and Cr as a luminescence center in an amount of 0.001 mol% or more with respect to the total amount of substance of the second crystal phase; The first crystal phase contains a halide represented by a chemical formula LiX, where X is an element containing at least one of Cl, Br, and I.

3. A scintillator according to claim 1 or 2; a light receiving element for receiving scintillation light emitted by the scintillator; A radiation measuring device comprising:

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