CN110824533A

CN110824533A - Radiation detector with special light-emitting surface sodium-doped cesium iodide scintillation crystal

Info

Publication number: CN110824533A
Application number: CN201911189830.2A
Authority: CN
Inventors: 魏娟
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-11-28
Filing date: 2019-11-28
Publication date: 2020-02-21

Abstract

The invention relates to a radiation detector with a scintillation crystal with a special light-emitting surface, wherein the shape of the light-emitting surface of the scintillation crystal is optimized, an optical light guide structure is formed by the light-emitting end of the scintillator, the specific shape design considers the matching with the refractive index and the light-emitting wave band of the scintillation crystal, the light-emitting probability of the emergent light which is totally reflected and emitted for the first time in the prior art can be increased, the measurement efficiency and the measurement precision are improved, and the detection performance can be further improved particularly when a high-performance detector is developed.

Description

Radiation detector with special light-emitting surface sodium-doped cesium iodide scintillation crystal

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 has played an important role in many fields, such as nuclear power plant and thermal power plant radiation measurement, continuous measurement of radiation dose at a measurement site; the radiation measurement is widely applied to radioactive places such as radioactivity monitoring, industrial nondestructive inspection, hospital treatment and diagnosis, isotope application, waste recovery and the like, the radiation measurement monitors radiation to prevent radiation from generating harm on one hand, and plays a role in monitoring and calculating diagnosis and treatment on the other hand.

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.

A typical structure of a conventional scintillation crystal radiation measuring apparatus is shown in fig. 1, in which a scintillation crystal is used as a detection crystal, a reflective layer is disposed on a surface facing an emission source and around the surface, and the remaining surface is an excited light emitting surface, and the excited light emitting surface is connected to a photosensor (typically, a photomultiplier tube, for example) through an optical coupling structure, and the photosensor photomultiplier tube is respectively connected to a high voltage divider and a preamplifier; the input high voltage is loaded on the photomultiplier through the high voltage divider, and the output signal is processed by the preamplifier, the linear amplifier and the multi-channel analyzer in sequence to form the final output signal. Such detectors using scintillation crystals have also been well studied by those skilled in the art because of their ease of use and simplicity of construction to provide the most widely used detectors.

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

The technical team of the applicant researches and discovers the technical thought dead angle in the prior art, the prior art generally uses an external reflecting film and an external antireflection film to improve the emergent efficiency and the emergent time of scintillation light, however, the prior art actually ignores that a scintillation crystal is also a part of an important light guide component, and particularly after the applicant team provides a latest scheme for guiding the scintillation light by a coating film and a lens group, the applicant team unexpectedly discovers that the influence of the scintillation crystal on the light emergent efficiency also becomes an important factor which can be considered.

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 proposed to be applied on the same day and combined with different techniques to form a patent layout, the prior art mentioned in the corresponding background art is not necessarily the one that has been disclosed to the public, and some of the prior art that is not disclosed when the technical team of the applicant researches the corresponding technique, so neither the prior art mentioned in the background art nor the claimed prior art can be taken as the evidence that the related art has been known to the public, and can not be the evidence of common knowledge.

Disclosure of Invention

In view of the problems and bottlenecks in the prior art, the present invention provides a radiation detector with a scintillation crystal having a special light emitting surface, and mainly aims to provide a structure capable of further improving the light emitting rate when developing a high performance radiation detector, so as to improve the detection efficiency and precision.

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

the utility model provides a radiation detector with special plain noodles scintillation crystal, includes scintillation crystal, photosensor, preamplification circuit and multichannel analysis appearance, and the scintillation crystal surface is provided with reflector layer and anti-reflection coating, and the reflector layer setting is on the surface except scintillation light emergence face, and anti-reflection coating sets up at scintillation light emergence face, the scintillation crystal is for mixing sodium cesium iodide crystal, and scintillation crystal and photosensor setting are in encapsulation casing, its characterized in that: the scintillation light emergent surface is provided with an aspheric convex structure matched with the scintillation light waveband of the sodium-doped cesium iodide crystal;

further, the main body of the scintillation crystal except for the scintillation light emergent surface is of a cylindrical structure, the axis of the cylinder is coincident with the central axis of the light receiving surface of the photosensor, and the convex shape of the scintillation light emergent surface meets 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=-0.59，k=7.93E-01，A4=3.37E+00，A6= -1.51E+02，A8= 3.67E+03，A10= -4.76E+04，A12= 3.51E+05，A14= -1.28E+06，A16= 1.65E+06；

further, the light sensor is a photomultiplier, and the distance between the light receiving surface of the photomultiplier and the scintillation light emitting surface is more than 1.4 mm;

further, an area of a light receiving surface of the photomultiplier tube is larger than an area of the scintillation light emitting surface by 20%.

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

the radiation detector in the prior art usually considers the external reflection and anti-reflection of the scintillator, and rarely starts from the shape and 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 wave band of the scintillation crystal, the emergent probability of emergent light which is totally reflected and is emergent for the first time in the prior art can be increased, the measurement efficiency and the measurement precision are improved, and the detection performance can be further improved particularly when a high-performance detector is developed.

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 a specially designed geometry of a scintillation light exit face of the present invention;

in the figure: r: radiation source S1: scintillation crystal light exit surface S2: scintillation crystal light reflection surface S3: light-receiving surface 1 of photomultiplier: scintillation crystal 2: the optical sensor 3: internal circuit 4: the detector packaging shell 5: external power supplies and circuits.

Detailed Description

The present invention is further explained with reference to the accompanying drawings, and as shown in fig. 2, a radiation detector with a scintillation crystal with a special light emitting surface comprises a scintillation crystal 1, a photosensor 2, a preamplifier circuit and a multichannel analyzer 3, wherein a light reflecting layer and an anti-reflection layer are arranged on the surface of the scintillation crystal, the light reflecting layer is arranged on a surface S2 except for the scintillation light emitting surface, the anti-reflection layer is arranged on the scintillation light emitting surface S1, and the scintillation crystal is a sodium-doped cesium iodide csi (na) crystal.

Sodium-doped cesium iodide CsI (Na) is one of conventional scintillation crystals known in the prior art, the refractive index of the crystal is 1.84, the peak wavelength is 420nm, low-energy visible photons generated inside the crystal are distributed isotropically, when the visible photons generated inside the crystal reach the end scintillation light emitting surface S1, under the influence of the transmittance of the light emitting surface, part of the photons are reflected back to the inside of the crystal and are emitted after being reflected for multiple times, the primary light emitting rate of the crystal is reduced, the number of the detected photons reaching PMT for the first time is reduced, the time resolution of the detector is influenced, in order to improve the primary light emitting rate of the large-angle photons of the detector and improve the time resolution of the detector, the shape design of the light emitting surface of a large amount of data is performed around the wavelength of 420nm, and the aspheric surface shape as shown in FIG. 3 is obtained through actual tests and performance comparison, although FIG. 3, the actual parameters satisfy the following relationship:

the main body of the scintillation crystal except the scintillation light emitting surface S1 is a cylinder structure, the axis of the cylinder is coincident with the central axis of the light receiving surface S3 of a photosensor (a photosensor is taken as an experimental device in the design, however, other photosensors such as a silicon photocell well known to those skilled in the art can also be applied), and the convex shape of the scintillation light emitting surface satisfies the following aspheric surface formula:

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.

In combination with the emitting angle of the aspheric surface, the distance between the light receiving surface of the photomultiplier and the scintillation light emitting surface is inconsistent with the traditional experience, the performance improvement within 1.4mm is not obvious through the test, the performance is improved after the distance is larger than 1.4mm, at the moment, the light receiving surface of the photomultiplier needs to be large enough to cover the emitting range of the emitting light, and when the distance is larger than 1.4mm, the area of the light receiving surface of the photomultiplier is at least 20% larger than that of the scintillation light emitting surface to completely receive the emitted scintillation light.

Compared with a large amount of experimental data, the average data of the design comparison experiment of the invention is as follows, except that the related design of the crystal scintillation light emitting surface is different, and other conditions are the same, the design of the invention is not adopted, the average reflectivity of the crystal scintillation light emitting surface reaches about 55% when the angle is more than 48 degrees, the total reflection rapidly occurs along with the increase of the angle, and the total reflection can not be emitted once, but the once emitting rate is improved by about 18% by adopting the design of the invention, and the loss of the counting rate on the whole detection efficiency due to the time resolution is reduced by about 3%.

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

1. The utility model provides a radiation detector with special plain noodles scintillation crystal, includes scintillation crystal, photosensor, preamplification circuit and multichannel analysis appearance, and the scintillation crystal surface is provided with reflector layer and anti-reflection coating, and the reflector layer setting is on the surface except scintillation light emergence face, and anti-reflection coating sets up at scintillation light emergence face, the scintillation crystal is for mixing sodium cesium iodide crystal, and scintillation crystal and photosensor setting are in encapsulation casing, its characterized in that: the scintillation light emergent surface is provided with an aspheric convex structure matched with the scintillation light waveband of the sodium-doped cesium iodide crystal.

2. The radiation detector of claim 1, wherein: the main body of the scintillation crystal except the scintillation light emergent surface is of a cylindrical structure, the axis of the cylinder is superposed with the central axis of the light receiving surface of the optical sensor, and the convex shape of the scintillation light emergent surface meets the following aspheric surface formula:

R=-0.59，k=7.93E-01，A4=3.37E+00，A6= -1.51E+02，A8= 3.67E+03，A10= -4.76E+04，A12= 3.51E+05，A14= -1.28E+06，A16= 1.65E+06。

3. the radiation detector of claim 1, wherein: the light sensor is a photomultiplier, and the distance between the light receiving surface of the photomultiplier and the scintillation light emitting surface is larger than 1.4 mm.

4. The radiation detector of claim 1, wherein: the area of the light receiving surface of the photomultiplier is greater than 20% of the area of the scintillation light emitting surface.