CN108152851B

CN108152851B - Fast and slow neutron composite detector

Info

Publication number: CN108152851B
Application number: CN201711205461.2A
Authority: CN
Inventors: 王婷婷; 汲长松; 张庆威
Original assignee: China Nuclear Control System Engineering Co ltd
Current assignee: China Nuclear Control System Engineering Co ltd
Priority date: 2017-11-27
Filing date: 2017-11-27
Publication date: 2020-11-20
Anticipated expiration: 2037-11-27
Also published as: CN108152851A

Abstract

The invention relates to a fast and slow neutron composite detector, which has a cylindrical plastic scintillator as a main body structure, wherein blind holes are punched in the plastic scintillator and are uniformly and hierarchically arranged; placing a lithium glass scintillation column in the blind hole, and coupling the lithium glass scintillation column with the contact surface of the plastic scintillator by using an optical coupling agent; the optical window surface of the plastic scintillator is polished, and other outer surfaces are polished; the plastic scintillator is coated with a reflecting layer except the light window, and the outside of the reflecting layer is covered by the shell; the plastic scintillator light window surface and the light window are sealed by adopting optical cement, the light window is used as a light guide-out surface, and the scintillation light is guided out by the light window. The plastic scintillator is used for measuring incident fast neutrons, the lithium glass adopts a multilayer structure, the number of layers increases from inside to outside layer by layer, and the number of layers is preferably three. The outer layer and the inner layer are used for detecting incident slow neutrons, the inner layer and the central lithium glass can measure slow neutrons after plastics are moderated, and meanwhile, the sensitivity of the incident fast neutrons and the sensitivity of the slow neutrons are improved.

Description

Fast and slow neutron composite detector

Technical Field

The invention relates to the field of neutron detection in nuclear radiation measurement technology, in particular to a fast and slow neutron composite detector.

Background

Neutron measurement is an important content in nuclear radiation monitoring technology, and various measuring instruments such as a neutron fluence rate instrument, a neutron energy spectrometer, a neutron dose equivalent instrument and the like have been developed according to different applications. The neutron detectors commonly used mainly have³He proportional counter, BF₃A proportional counter,⁶Li glass scintillators, plastic scintillators, liquid scintillators, and the like. The detectors commonly used at the present stage are only sensitive to neutrons in a specific energy band, and are extremely low in sensitivity to other energy bands, for example, the first three items are slow neutron detectors, and the last two items are fast neutron detectors. For neutron detection, a detector which has high sensitivity and fast response to both slow neutrons and fast neutrons is required, which is a necessary subject.

At present, plastic scintillator medium carriers have been studied at home and abroad⁶The method of Li nuclide introduces slow neutron detection nuclide into fast neutron detector. Theoretical calculation and experiments are carried out to achieve the effect of improving the neutron sensitivity of the plastic scintillator below 0.5 MeV. But with the mixing⁶The Li concentration is improved, the transparency of the plastic scintillator is obviously reduced, the neutron sensitivity is obviously reduced, and the process needs to be improved. Additional load⁶The Li plastic scintillator has complex manufacturing process and needs to be preparedIntroduction during the polymerization of plastics⁶The species of Li is a nuclear species,⁶li is easy to distribute unevenly, so that the detectors have different properties.

Disclosure of Invention

The invention aims to: aiming at the problems that the neutron detector in the prior art only has high sensitivity to neutrons in different energy bands and cannot meet the requirement of measuring fast neutrons and slow neutrons simultaneously, the fast neutron detector and the slow neutron detector which have the advantages of high sensitivity, simple process and small environmental influence are provided.

The technical scheme of the invention is as follows: a fast and slow neutron composite detector has a cylindrical plastic scintillator, blind holes are punched in the plastic scintillator, and the blind holes are uniformly and hierarchically arranged; placing a lithium glass scintillation column in the blind hole, and coupling the lithium glass scintillation column with the contact surface of the plastic scintillator by using an optical coupling agent; the optical window surface of the plastic scintillator is polished, and other outer surfaces are polished; the plastic scintillator is coated with a reflecting layer except the light window, and the outside of the reflecting layer is wrapped by the shell; the plastic scintillator light window surface and the light window are sealed by optical cement, and the scintillation light is led out by the light window.

The lithium glass scintillation column is arranged in a multilayer structure, and the number of layers increases from inside to outside layer by layer.

The depth of the blind hole is consistent with the length of the lithium glass scintillation column, and the diameter of the hole is slightly larger than that of the lithium glass scintillation column.

The lithium glass scintillation column is rich in⁶A Li core, a scintillator is activated by cerium; and the outer surface of the lithium glass scintillation column is subjected to polishing treatment.

The size of the plastic scintillator is 10 mm-100 mm in diameter and 10mm-200mm in length.

The size of the lithium glass scintillation column is phi 1 mm-phi 10mm in diameter and 5mm-200mm in length.

The reflecting layer is used for preventing light from escaping and improving the light collection efficiency.

The shell is subjected to light shielding and anti-interference treatment in advance, and the size of the shell is adapted to the size of the composite detector.

The optical window is an organic glass light guide.

The invention has the following remarkable effects:

the multi-column high-sensitivity fast and slow neutron detector provided by the invention utilizes a plurality of lithium glass scintillation columns which are arranged in a plastic scintillator in a layered manner to carry out neutron detection, and has the following benefits and effects:

1) can measure incident fast and slow neutrons simultaneously, and has high neutron sensitivity

Plastic scintillators are used to measure incident fast neutrons, and lithium glass is distributed in multiple layers, preferably three layers. The outer layer and the inner layer are used for detecting incident slow neutrons, the inner layer and the central layer can measure fast neutrons moderated by the plastic scintillator, and meanwhile, the sensitivity of the incident fast neutrons and the sensitivity of the incident slow neutrons are improved.

2) Improving gamma inhibition performance

The detector is a neutron detector, and the interference of gamma on the measurement is reduced as much as possible. The product nuclei in the neutron nuclear reaction are heavy charged particles, the range is short, and the lithium glass adopts a multi-column structure, so that the neutron sensitivity can be effectively improved, and the gamma interference can be reduced.

3) Is not influenced by lithium concentration and has flexible adjustment of neutron sensitivity

The transparency of the traditional lithium-loaded plastic scintillator is reduced along with the increase of lithium concentration, and the neutron sensitivity is greatly limited. The detector can not be influenced by lithium concentration, lithium scintillation columns combined at different positions are distributed according to specific requirements, and neutron sensitivity can be flexibly adjusted.

4) The detector has simple manufacturing process and isotropy

The lithium glass scintillator does not deliquesce, does not need to be packaged, only needs optical coupling when manufacturing the combined detector, and greatly simplifies the process compared with the traditional lithium-carrying process which needs to introduce nuclides in the plastic polymerization process. And in the scintillator of the present invention⁶The Li nuclide is uniformly distributed, and the detector has the same property.

Drawings

FIG. 1 is a bottom view of a composite probe;

FIG. 2 is a front view of a multi-column composite detector;

FIG. 3 is a schematic diagram of a blind hole in a plastic scintillator;

in the figure: 1. plastic scintillator, 2 lithium glass scintillation column, 3 light window, 4 reflecting layer and 5 casing.

Detailed Description

The fast and slow neutron composite detector of the invention is further described in detail with reference to the accompanying drawings and specific embodiments.

A fast and slow neutron composite detector has a cylindrical plastic scintillator 1 as a main body structure, wherein blind holes are punched in the plastic scintillator 1 and are uniformly and hierarchically arranged; a lithium glass scintillation column 2 is placed in the blind hole, and the contact surface of the lithium glass scintillation column 2 and the plastic scintillator 1 is coupled by using an optical coupling agent; the optical window surface of the plastic scintillator 1 is polished, and other outer surfaces are polished; the plastic scintillator 1 is coated with a reflecting layer 4 except for a light window, and the outside of the reflecting layer 4 is wrapped by a shell 5; the optical window surface of the plastic scintillator 1 and the optical window 3 are sealed by optical cement, and the scintillation light is led out from the optical window 3.

The lithium glass scintillation column 2 is arranged in a multilayer structure, and the number of layers increases from inside to outside layer by layer.

The blind holes are arranged into three layers, 12 blind holes are arranged on the outer layer, 6 blind holes are arranged on the inner layer, and 1 blind hole is arranged in the center. The depth of the blind hole is consistent with the length of the lithium glass scintillation column 2, and the diameter of the hole is slightly larger than that of the lithium glass scintillation column 2.

The lithium glass scintillation column 2 is rich in⁶A Li core, a scintillator is activated by cerium; and the outer surface of the lithium glass scintillation column 2 is polished.

The size of the plastic scintillator 1 is 10mm to 100mm in diameter and 10mm to 200mm in length, preferably 45mm x 75mm in diameter. The size of the lithium glass scintillation column 2 is phi 1 mm-phi 10mm in diameter, 5mm-200mm in length, and preferably phi 4mm x 70 mm.

The reflecting layer 4 is used for preventing light from escaping and improving the light collection efficiency. The shell 5 is subjected to light shielding and anti-interference treatment in advance, and the size of the shell is adapted to the size of the composite detector. The optical window 3 is an organic glass light guide.

The nuclear reaction method is to detect neutrons by detecting charged products generated by nuclear reaction between neutrons and nuclides. The nuclear reaction method is only suitable for detecting slow neutrons. The nuclear back-flushing method is based on elastic scattering of fast neutrons to light nuclei to generate charged back-flushing nuclei, and detection neutrons are detected through the detection back-flushing nuclei.

The plastic scintillator detects fast neutrons by a nuclear back-flushing method, and the generated back-flushed protons deposit energy in the plastic to form flashing light. The fast neutrons are subjected to multiple elastic scattering, and then the energy is reduced, and the fast neutrons are moderated into slow neutrons. Plastic scintillators are only suitable for detecting fast neutrons, where the sensitivity of the neutrons drops very fast at energies less than 1 MeV. The lithium glass scintillator detects slow neutrons using a nuclear reaction method. The generated charged particles can be deposited energetically in the glass scintillator to form scintillating light.

The working process is as follows: after the neutrons enter the scintillator of this embodiment, the incident slow neutrons preferentially react with the outer-layer lithium glass scintillation column, and part of the undetected slow neutrons can react with the inner-layer lithium glass, so that the product nuclei can be deposited in the glass scintillator to form scintillation light. The slow neutron efficiency is improved due to the layered structure; the incident fast neutrons and the plastic scintillator H nucleus generate elastic scattering, and the generated recoil protons deposit energy in the plastic to form scintillation light. The energy of fast neutrons is reduced after multiple elastic scattering in the plastic scintillator, and the moderated neutrons can reach the inner position of the detector through a section of deceleration length and are detected by the inner layer and the central lithium glass column, so that the fast neutron detection efficiency is improved.

Detecting fast neutrons by a plastic scintillator; the outer and inner lithium glass scintillation columns detect slow neutrons, and in addition, fast neutrons can still be detected by the inner and central lithium glass scintillation columns after being elastically scattered in the plastic scintillator to become slow neutrons. The slow neutron and fast neutron efficiencies can be simultaneously improved.

In this embodiment, the lithium glass has a multi-pillar structure. Glass scintillators have some response to gamma, which is detrimental to detecting neutrons. The column structure can effectively reduce the output amplitude of gamma signals and reduce the interference of gamma. The multi-column composite detector provided by the invention can be applied to the field of high-sensitivity fast and slow neutron detection.

Claims

1. A fast and slow neutron composite detector is characterized in that: the main body structure is a cylindrical plastic scintillator (1), blind holes are punched in the plastic scintillator (1), and the blind holes are uniformly and hierarchically arranged; a lithium glass scintillation column (2) is placed in the blind hole, and the contact surface of the lithium glass scintillation column (2) and the plastic scintillator (1) is coupled by using an optical coupling agent; the optical window surface of the plastic scintillator (1) is polished, and other outer surfaces are polished; the plastic scintillator (1) is coated with a reflecting layer (4) except for a light window, and the outside of the reflecting layer (4) is wrapped by a shell (5); the optical window surface of the plastic scintillator (1) and the optical window (3) are sealed by optical cement, and the scintillation light is led out by the optical window (3).

2. A fast and slow neutron composite detector as in claim 1, wherein: the lithium glass scintillation column (2) is arranged in a multilayer structure, and the number of layers increases from inside to outside layer by layer.

3. A fast and slow neutron composite detector as in claim 1, wherein: the depth of the blind hole is consistent with the length of the lithium glass scintillation column (2), and the diameter of the blind hole is slightly larger than that of the lithium glass scintillation column (2).

4. A fast and slow neutron composite detector as in claim 1, wherein: the lithium glass scintillation column (2) is rich in⁶A Li core, a scintillator is activated by cerium; the outer surface of the lithium glass scintillation column (2) is polished.

5. A fast and slow neutron composite detector as in claim 1, wherein: the size of the plastic scintillator (1) is 10 mm-100 mm in diameter and 10mm-200mm in length.

6. A fast and slow neutron composite detector as in claim 1, wherein: the lithium glass scintillation column (2) has the size of diameter phi 1 mm-phi 10mm and the length of 5mm-200 mm.

7. A fast and slow neutron composite detector as in claim 1, wherein: the reflecting layer (4) is used for preventing light from escaping and improving the light collection efficiency.

8. A fast and slow neutron composite detector as in claim 1, wherein: the shell (5) is subjected to light shielding and anti-interference treatment in advance, and the size of the shell is adapted to the size of the composite detector.

9. A fast and slow neutron composite detector as in claim 1, wherein: the optical window (3) is an organic glass light guide.