CN110737014A - europium-doped calcium fluoride scintillation crystal radiation detector with exit surface matched with lens set - Google Patents

Abstract

The invention relates to scintillation crystal radiation detectors with special light-emitting surfaces matched with lens groups, which construct a -angle and large-depth-of-field lens group matched with each other, increase the collection efficiency of a photosensor on scintillation light and improve the energy resolution, and the specific parameter design considers the matching with the emergent wave band of a scintillation crystal, can increase an incident light sensor after focusing and collecting the scintillation light, improve the energy resolution, correspondingly design the shape of the light-emitting surface of the scintillation crystal matched with the lens group, further improve the measurement efficiency and the measurement precision, and particularly can improve the detection performance by steps when developing a high-performance detector.

Description

europium-doped calcium fluoride scintillation crystal radiation detector with exit surface matched with lens set

Technical Field

The present invention relates to the measurement of nuclear or X-ray radiation, and in particular to the measurement of X-ray radiation, gamma-ray radiation, corpuscular radiation or cosmic radiation, and in particular to scintillation detectors in which the scintillator is a crystal in the measurement of the intensity of the radiation.

Background

Radiation measurement plays an important role in many fields, such as nuclear power station thermal power plant radiation measurement, continuous measurement of radiation dose at a measurement site, industrial and civil buildings, building decoration, building material production and manufacturing, radiation measurement of various building materials, geological exploration, geological prospecting and mine radiation measurement, a channel for security inspection of rays, which can help customs, airport, border inspection and safety inspection of important meeting places, radiation measurement and radiation therapy (CT, PET, ray knife and the like) used in medical treatment need diagnosis and treatment by measuring radiation intensity, is widely applied to radioactive places such as radioactive monitoring, industrial nondestructive inspection, treatment and diagnosis of hospitals, isotope application, waste recovery and the like, radiation measurement monitors radiation to prevent radiation damage, and monitors, diagnoses and calculates.

Radiation detection is the most fundamental research field of radiation measurement, the basic principle of radiation detectors is that radiation detection is performed by using an ionization excitation effect or other physical or chemical changes caused by radiation in gas, liquid or solid, the known types of detectors include gas detectors, scintillation detectors and semiconductor detectors, the gas detectors are complex in structure and the semiconductor detectors are not ideal in detection efficiency, the scintillation detectors are the most commonly used detectors at present, the scintillation detectors are strictly classified into liquid scintillation detectors and solid scintillation detectors, the liquid scintillation detectors are much less portable than the solid scintillation detectors, and the liquid scintillation detectors are basically used for laboratory research, and the solid detectors for measuring radiation by using scintillation crystals are the most researched detector types in the field.

The conventional radiation measuring device with a scintillation crystal is typically configured as shown in fig. 1, and uses a scintillation crystal as a detection crystal, and has a reflective layer disposed on a surface facing an emission source and around the emission source, and a surface is a light-emitting surface, and the surface is connected to a photosensor (typically, a photomultiplier tube) through a light coupling structure, and the photosensor photomultiplier tube is respectively connected to a high voltage divider and a preamplifier, and an input high voltage is applied to the photomultiplier tube through the high voltage divider, and an output signal is sequentially processed by the preamplifier, a linear amplifier and a multichannel analyzer to form a final output signal.

At present, how to increase the energy resolution and the time resolution of the detector by steps is a technical bottleneck for developing a high-performance detector.

In order to improve the performance of the detector, the applicant's technical team develops a new approach and creatively proposes an external light guide concept, the conventional technical idea usually does not aim at the optical path between the scintillation light emitting surface of the crystal and the light sensor, and usually focuses on how to avoid the damage of the ray to the light sensor, which requires changing the optical path or setting a corresponding lens for light transmission when using the optical fiber connection, and setting a corresponding lens unit when imaging is required, however, the applicant's team finds in experiments that in the counting type radiation detector without imaging as shown in fig. 1, the detection efficiency of the photomultiplier tube can be significantly improved and the noise can be reduced after passing through a specially designed lens group, and as is well known, the design of the lens group of the combination of a plurality of lens groups is very complicated, the technical prejudicial prejudice that, in general, the technical personnel in the art think that designing the lens group for improving the corresponding efficiency of the detector itself in a limited space is only a simple description, and does not give any applicable core design parameters, and even if the technical team of the improvement of the lens group in the conventional technical design scheme is only briefly described in a few prior arts, and a great deal with the research data of the technical scheme of the technical system design of the application of the high-based on the experimental system, and the research scheme () is proposed by which the application of the present application.

On the basis of improving the detection efficiency of the detector by using the lens group, researches of the technical team of the applicant find a dead angle of technical ideas in the prior art, the prior art generally uses an external reflecting film and an external antireflection film to improve the emergence efficiency and the emergence time of scintillation light, however, the scintillation crystal itself is actually ignored and is an important part of a light guide assembly, especially after the team of the applicant proposes a latest scheme for guiding the scintillation light by using the lens group, the influence of the scintillation crystal itself on the light emergence efficiency becomes an important factor which can be considered, and the technical team of the applicant proposes a matching relationship between the shape of the emergence surface of the scintillator and the lens group through breakthrough design, and can improve the energy resolution and the time resolution of the detector by steps.

It should be noted that, after more than three years of research in this field, the technical team of the applicant has arrived at a plurality of technical achievements, and in order to avoid the prior art that may become the later application or the conflicting application, the technical achievements are purposely combined between different technologies to form a patent layout, and the corresponding prior art mentioned in the background art is not a publicly disclosed technology, and some is an internal prior art that is not disclosed when the technical team of the applicant researches the corresponding technology, so neither the technology mentioned in the background art nor the claimed prior art can be taken as evidence that the related technology has been publicly known, and can not be taken as evidence of common general knowledge.

Disclosure of Invention

In view of the above problems and bottlenecks in the prior art, the present invention provides scintillation crystal radiation detectors with special light-emitting surfaces matched with lens sets, and mainly aims to provide structures which can further improve light collection rates when developing high performance radiation detectors, so as to improve detection efficiency and precision.

In order to achieve the purpose, the invention is realized by the following technical scheme:

scintillation crystal radiation detector with special light-out surface matched with lens group, including scintillation crystal, optical sensor, preamplification circuit and multi-channel analyzer, the scintillation crystal surface is equipped with reflection layer and reflection reducing layer, the reflection layer is set on the surface except scintillation light-out surface, the reflection reducing layer is set on the scintillation light-out surface, the scintillation crystal is europium-doped calcium fluoride crystal, the scintillation crystal and optical sensor are set in the packaging shell, the multi-channel analyzer is set outside the shell, characterized in that a lens group matched with the wave band of the scintillation light of europium-doped calcium fluoride crystal is set between the scintillation light-out surface and the optical sensor, the scintillation light-out surface has aspheric surface convex structure matched with the scintillation light wave band of europium-doped calcium fluoride crystal;

, the scintillation crystal has a cylindrical body structure except for the scintillation light emergent surface, the axis of the cylindrical body coincides with the optical axis of the lens group and the central axis of the light receiving surface of the light sensor, the lens group sequentially comprises a th lens, a second lens, a third lens, a fourth lens and a fifth lens along the scintillation light emergent direction, the two side surfaces of each lens are aspheric surfaces, and the following aspheric surface equation is satisfied:

y＝(x²/R)/（1+（1－(k+1) (x²/R²)）^1/2+A4x⁴+A6x⁶+A8x⁸+A10x¹⁰+A12x¹²+A14x¹⁴+A16x¹⁶，

wherein R is a radius of curvature (length in mm in absolute value) on the central axis, k is a conic coefficient, A4, A6, A8, A10, A12, A14, A16 are aspherical coefficients,

the values are as follows:

lens surface

R

k

A4

A6

A8

A10

A12

A14

A16

1-R

0.80

-5.17E-01

7.58E-02

5.31E-02

1.45E-01

-9.98E-01

-1.71E-01

5.71E+00

-1.59E+01

1-L

4.46

4.29E-01

-3.83E-01

1.11E+00

-1.78E+00

-9.42E-01

-1.94E+00

-8.56E-01

9.23E+00

2-R

-12.10

2.01E+02

-1.07E-01

1.55E+04

-2.71E+00

1.72E+00

2.59E+00

-2.33E+01

4.54E+01

2-L

3.58

2.59E-01

1.38E-01

1.16E+00

-2.40E+00

1.27E-01

1.22E+01

5.85E+01

-1.21E+02

3-R

-22.83

1.70E-03

-5.67E-01

-1.93E-01

1.63E+00

-1.52E+01

1.46E+01

1.72E+02

-3.05E+02

3-L

274.06

-7.53E+01

-4.41E-01

-7.60E-02

2.83E+03

-1.83E+00

-2.38E+04

3.22E+01

-3.72E+01

4-R

-2.68

2.14E+04

5.54E-05

-4.18E-02

2.79E-01

-9.71E-01

1.25E+00

-3.09E-01

-1.84E-01

4-L

-0.63

-2.62E+00

-1.30E-01

1.12E-01

2.17E+03

-3.12E-01

1.12E-01

4.13E-02

-2.60E-02

5-R

-2.25

-1.99E-01

-2.71E-01

2.38E-01

-9.04E-02

1.65E-02

-1.09E-04

-3.36E-04

2.04E-06

5-L

0.90

-7.97E-02

-1.71E-01

1.30E-01

-7.23E-02

2.07E-02

-1.40E-03

-8.52E-04

1.46E-04

Wherein N-R columns in the lens surface columns represent the object side surface of the Nth lens, and N-L represents the image side surface of the Nth lens;

the convex shape of the glittering light emitting surface satisfies the following aspheric surface formula:

y＝(x²/R)/（1+（1－(k+1) (x²/R²)）^1/2+A4x⁴+A6x⁶+A8x⁸+A10x¹⁰+A12x¹²+A14x¹⁴+A16x¹⁶，

wherein, R is the curvature radius (the length unit of the absolute value is mm) on the central axis, k is the cone coefficient, A4, A6, A8, A10, A12, A14 and A16 are aspheric coefficients, and the values are as follows:

R=-3.83，k=1.58966，A4=0.00111，A6=-0.00602，A8=0.02353，A10=-0.0391，A12=0.02458，A14=-0.00308，A16=-0.00092；

, the light sensor is a silicon photomultiplier;

, the focal lengths of the to fifth lenses are respectively 1.79 mm, -4.37 mm, -31.78 mm, 1.46mm, -1.22 mm;

, the thickness of the th lens to the fifth lens is 0.37 mm, 0.19 mm, 0.11 mm, 0.43 mm and 0.24mm respectively.

, the distance between the object side surface of the lens and the flash light exit surface is more than 0.6 mm;

further , the object side surface of the lens is larger than 20% of the area of the scintillator exit surface.

Compared with the prior art, the invention has the advantages that:

1) the invention breaks through the traditional technical thought, overcomes the inherent defects that the data volume is too large and is difficult to select and optimize when the lens group is designed aiming at the main emergent wave band of the scintillation crystal, constructs a matched -angle and large-depth-of-field lens group, increases the collection efficiency of the optical sensor to the scintillation light and improves the energy resolution, and the specific parameter design considers the matching with the emergent wave band of the scintillation crystal, can increase the incident optical sensor after focusing and collecting the scintillation light, improves the energy resolution, correspondingly improves the measurement efficiency and the measurement precision, and especially can further improve the detection performance by steps when developing a high-performance detector;

2) the radiation detector in the prior art usually considers the external reflection and the permeability increase of a scintillator, and rarely starts from the shape and the performance of the scintillation crystal, the invention initiatively provides a concept of optimizing the shape of the light emergent surface of the scintillation crystal, an optical light guide structure is formed by the emergent end of the scintillator, the specific shape design of the optical light guide structure considers the matching with the emergent waveband of the scintillation crystal, the emergent probability of emergent light which is totally reflected by th emergent light in the prior art can be increased, the measurement efficiency and the measurement precision are improved, when the optical light guide structure is matched with a lens, the improvement is particularly obvious, and when a high-performance detector is developed, the detection performance can be improved by steps.

Drawings

FIG. 1 is a schematic diagram of a prior art radiation detector;

FIG. 2 is a schematic view of a radiation detector of the present invention;

FIG. 3 is a schematic diagram of the lens geometry and the lens exit face of the present invention (the relative size relationship is not considered in the figure);

in the figure, R is a radioactive source L, a lens group S1, a scintillation crystal light emitting surface S2, a scintillation crystal light reflecting surface S3, a light receiving surface 1 of a photomultiplier, a scintillation crystal 2, a photosensor 3, an internal circuit 4, a detector packaging shell 5, an external power supply and a circuit, L1-L5, and a fifth lens .

Detailed Description

The invention will be further described with reference to , as shown in fig. 2, scintillation crystal radiation detectors with special light-emitting surfaces matched with lens groups include a scintillation crystal 1, a photosensor 2, a preamplifier circuit and multi-channel analyzers 3 and 5, the scintillation crystal surface is provided with a light-reflecting layer and an anti-reflection layer, the light-reflecting layer is arranged on a surface S2 except a scintillation light-emitting surface, the anti-reflection layer is arranged on a scintillation light-emitting surface S1, the scintillation crystal is a europium-doped calcium fluoride crystal, the scintillation crystal 1 and the photosensor 3 are arranged in a packaging shell 4, the multi-channel analyzer is arranged outside the shell, and a lens group L matched with a waveband of scintillation light of the europium-doped calcium fluoride crystal is arranged between the scintillation light-emitting surface S2 and the photosensor 3.

Europium-doped calcium fluoride is of a conventional scintillation crystal known in the prior art, low-energy visible photons generated inside the crystal are distributed isotropically, when the visible photons generated inside the crystal reach a tail scintillation light emitting surface S1, the emission angle range is large, the energy resolution of a detector is affected, in order to improve the collection rate of large-angle photons of the detector and improve the energy resolution of the detector, a lens group design of a large amount of data is carried out around the wavelength of europium-doped calcium fluoride scintillation light, and an aspheric shape lens group as shown in FIG. 3 is obtained through practical tests and performance comparison, of course, FIG. 3 is only a schematic diagram and does not represent absolute distance and relative size relationships, and it is known in the art that aspheric relationships use the intersection point of an aspheric surface and an axis as an origin, only aspheric coordinates of the scintillation light emitting surface are shown in FIG. 3, y axes of coordinate systems formed by other aspheric relationships do not coincide with y axes of coordinates of the aspheric surface of the scintillation light emitting surface, and practical parameters satisfy the following relationships:

the main body of the scintillation crystal except for the scintillation light emergent surface is of a cylindrical structure, the axis of the cylindrical structure coincides with the optical axis of the lens group and the central axis of the light receiving surface of the optical sensor, the lens group sequentially comprises a th lens L1, a second lens L2, a third lens L3, a fourth lens L4 and a fifth lens L5 along the scintillation light emergent direction, the two side surfaces of each lens are aspheric surfaces, and the following aspheric surface equations are satisfied:

y＝(x²/R)/（1+（1－(k+1) (x²/R²)）^1/2+A4x⁴+A6x⁶+A8x⁸+A10x¹⁰+A12x¹²+A14x¹⁴+A16x¹⁶，

wherein R is a radius of curvature (length in mm in absolute value) on the central axis, k is a conic coefficient, A4, A6, A8, A10, A12, A14, A16 are aspherical coefficients,

the values are as follows:

lens surface

R

k

A4

A6

A8

A10

A12

A14

A16

1-R

0.80

-5.17E-01

7.58E-02

5.31E-02

1.45E-01

-9.98E-01

-1.71E-01

5.71E+00

-1.59E+01

1-L

4.46

4.29E-01

-3.83E-01

1.11E+00

-1.78E+00

-9.42E-01

-1.94E+00

-8.56E-01

9.23E+00

2-R

-12.10

2.01E+02

-1.07E-01

1.55E+04

-2.71E+00

1.72E+00

2.59E+00

-2.33E+01

4.54E+01

2-L

3.58

2.59E-01

1.38E-01

1.16E+00

-2.40E+00

1.27E-01

1.22E+01

5.85E+01

-1.21E+02

3-R

-22.83

1.70E-03

-5.67E-01

-1.93E-01

1.63E+00

-1.52E+01

1.46E+01

1.72E+02

-3.05E+02

3-L

274.06

-7.53E+01

-4.41E-01

-7.60E-02

2.83E+03

-1.83E+00

-2.38E+04

3.22E+01

-3.72E+01

4-R

-2.68

2.14E+04

5.54E-05

-4.18E-02

2.79E-01

-9.71E-01

1.25E+00

-3.09E-01

-1.84E-01

4-L

-0.63

-2.62E+00

-1.30E-01

1.12E-01

2.17E+03

-3.12E-01

1.12E-01

4.13E-02

-2.60E-02

5-R

-2.25

-1.99E-01

-2.71E-01

2.38E-01

-9.04E-02

1.65E-02

-1.09E-04

-3.36E-04

2.04E-06

5-L

0.90

-7.97E-02

-1.71E-01

1.30E-01

-7.23E-02

2.07E-02

-1.40E-03

-8.52E-04

1.46E-04

Wherein N-R columns in the lens surface columns represent the object side surface of the Nth lens, and N-L represents the image side surface of the Nth lens;

the convex shape of the glittering light emitting surface satisfies the following aspheric surface formula:

y＝(x²/R)/（1+（1－(k+1) (x²/R²)）^1/2+A4x⁴+A6x⁶+A8x⁸+A10x¹⁰+A12x¹²+A14x¹⁴+A16x¹⁶，

wherein, R is the curvature radius (the length unit of the absolute value is mm) on the central axis, k is the cone coefficient, A4, A6, A8, A10, A12, A14 and A16 are aspheric coefficients, and the values are as follows:

R=-3.83，k=1.58966，A4=0.00111，A6=-0.00602，A8=0.02353，A10=-0.0391，A12=0.02458，A14=-0.00308，A16=-0.00092。

the focal lengths of the th to the fifth lenses are respectively 1.79 mm, -4.37 mm, -31.78 mm, 1.46mm, -1.22mm, and the thicknesses are respectively 0.37 mm, 0.19 mm, 0.11 mm, 0.43 mm and 0.24 mm.

The light sensor used in this experiment was a photomultiplier tube, but other light sensors known to those skilled in the art may be used.

In combination with the aspheric emission angle, the distance between the object-side surface of the th lens and the scintillation light emission surface is not from the traditional experience, performance improvement within 0.6mm is not obvious through experiments, performance is improved after the distance is larger than 0.6mm, at this time, the object-side surface of the th lens needs to be large enough to cover the emission range of the emitted light, when the distance is larger than 0.6mm, the area of the object-side surface of the th lens is larger than the area of the scintillation light emission surface by at least 20% to be capable of completely receiving the emitted scintillation light, fig. 3 is only a shape schematic, and a graph is not drawn according to the actual relative size.

It should be noted that, the aspheric formula is a known formula for lens design, and the difficulty lies in specific aspheric parameter design, after the parameters of the aspheric formula are disclosed, the conventional manufacturing technology in the prior art can easily implement the aspheric processing, and the specific processing manner is not described again.

Through comparison of a large amount of experimental data, the average data of the design comparison experiment of the invention is as follows, when other conditions are the same, the design of the lens group and the light emitting surface of the invention is not adopted, the detected number of the coincident events is reduced by more than 10%, and the arrangement of the visible lens group and the crystal light emitting surface can effectively improve the energy resolution of the system.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims (7)

1. scintillation crystal radiation detector with special light-emitting surface matched with lens set, including scintillation crystal, optical sensor, preamplification circuit and multi-channel analyzer, the surface of scintillation crystal is equipped with reflecting layer and reflection reducing layer, the reflecting layer is set on the surface except scintillation light-emitting surface, the reflection reducing layer is set on the scintillation light-emitting surface, the scintillation crystal is europium-doped calcium fluoride crystal, the scintillation crystal and optical sensor are set in the packaging shell, the multi-channel analyzer is set outside the shell, characterized in that a lens set matched with the wave band of the scintillation light of europium-doped calcium fluoride crystal is set between the scintillation light-emitting surface and the optical sensor, the scintillation light-emitting surface has aspheric surface convex structure matched with the scintillation light wave band of europium-doped calcium fluoride crystal.
2. 2. The radiation detector of claim 1, wherein:

   the main part of scintillation crystal except that scintillation light outgoing face is the cylinder structure, and the axis of cylinder and the optical axis of battery of lens and the central axis coincidence of the light receiving surface of light sensor, the battery of lens includes lens, second lens, third lens, fourth lens and fifth lens in proper order along scintillation light outgoing direction, and the both sides surface of each lens is the aspheric surface to satisfy following aspheric surface equation:

   y＝(x²/R)/（1+（1－(k+1) (x²/R²)）^1/2+A4x⁴+A6x⁶+A8x⁸+A10x¹⁰+A12x¹²+A14x¹⁴+A16x¹⁶，

   wherein R is a radius of curvature (length in mm in absolute value) on the central axis, k is a conic coefficient, A4, A6, A8, A10, A12, A14, A16 are aspherical coefficients,

   the values are as follows:

   lens surface R k A4 A6 A8 A10 A12 A14 A16 1-R 0.80 -5.17E-01 7.58E-02 5.31E-02 1.45E-01 -9.98E-01 -1.71E-01 5.71E+00 -1.59E+01 1-L 4.46 4.29E-01 -3.83E-01 1.11E+00 -1.78E+00 -9.42E-01 -1.94E+00 -8.56E-01 9.23E+00 2-R -12.10 2.01E+02 -1.07E-01 1.55E+04 -2.71E+00 1.72E+00 2.59E+00 -2.33E+01 4.54E+01 2-L 3.58 2.59E-01 1.38E-01 1.16E+00 -2.40E+00 1.27E-01 1.22E+01 5.85E+01 -1.21E+02 3-R -22.83 1.70E-03 -5.67E-01 -1.93E-01 1.63E+00 -1.52E+01 1.46E+01 1.72E+02 -3.05E+02 3-L 274.06 -7.53E+01 -4.41E-01 -7.60E-02 2.83E+03 -1.83E+00 -2.38E+04 3.22E+01 -3.72E+01 4-R -2.68 2.14E+04 5.54E-05 -4.18E-02 2.79E-01 -9.71E-01 1.25E+00 -3.09E-01 -1.84E-01 4-L -0.63 -2.62E+00 -1.30E-01 1.12E-01 2.17E+03 -3.12E-01 1.12E-01 4.13E-02 -2.60E-02 5-R -2.25 -1.99E-01 -2.71E-01 2.38E-01 -9.04E-02 1.65E-02 -1.09E-04 -3.36E-04 2.04E-06 5-L 0.90 -7.97E-02 -1.71E-01 1.30E-01 -7.23E-02 2.07E-02 -1.40E-03 -8.52E-04 1.46E-04

   Wherein N-R in the lens surface column represents an object side surface of the Nth lens, and N-L represents an image side surface of the Nth lens;

   the convex shape of the glittering light emitting surface satisfies the following aspheric surface formula:

   y＝(x²/R)/（1+（1－(k+1) (x²/R²)）^1/2+A4x⁴+A6x⁶+A8x⁸+A10x¹⁰+A12x¹²+A14x¹⁴+A16x¹⁶，

   wherein, R is the curvature radius (the length unit of the absolute value is mm) on the central axis, k is the cone coefficient, A4, A6, A8, A10, A12, A14 and A16 are aspheric coefficients, and the values are as follows:

   R=-3.83，k=1.58966，A4=0.00111，A6=-0.00602，A8=0.02353，A10=-0.0391，A12=0.02458，A14=-0.00308，A16=-0.00092。
3. 3. the radiation detector of claim 1, wherein: the light sensor is a silicon photomultiplier.
4. 4. The radiation detector as set forth in claim 1, wherein the th through fifth lenses have focal lengths of 1.79 mm, -4.37 mm, -31.78 mm, 1.46mm, -1.22mm, respectively.
5. 5. The radiation detector as set forth in claim 1, wherein the th through fifth lenses have thicknesses of 0.37 mm, 0.19 mm, 0.11 mm, 0.43 mm, and 0.24mm, respectively.
6. 6. The radiation detector as set forth in claim 1, wherein a distance between an object-side surface of the th lens and the scintillator exit surface is greater than 0.6 mm.
7. 7. The radiation detector as set forth in claim 1, wherein the object-side surface of the th lens is larger than 20% of the area of the scintillation light exit surface.

Images