Slow neutron conversion body and slow neutron detector

Abstract

The present application, pertaining to the field of slow neutron detection, relates to a slow neutron converter and a slow neutron detector. The slow neutron converter includes a substrate, the substrate including a plurality of holes extending along a first direction and insulating walls between the plurality of holes, wherein the plurality of holes are through holes. The slow neutron converter further includes a boron layer at least covering an exposed surface of the plurality of holes. The slow neutron converter and the slow neutron detector having the slow neutron converter according to the present disclosure are capable of maintaining a high slow neutron detection efficiency. In addition, the manufacturing complexity and manufacturing cost of the detector are reduced, and thus the effective, convenient and low-cost slow neutron detection is achieved.

Claims

1. A slow neutron detector, comprising: a slow neutron converter, wherein the slow neutron converter comprises: a substrate, comprising: a plurality of holes extending along a first direction, and insulating walls between the plurality of holes; and a boron layer, at least covering the exposed surface of the plurality of holes; wherein the plurality of holes are through holes and wherein the plurality of holes are filled with an ionization working gas; a cathode plate, disposed at one end of the slow neutron converter; an electron multiplier, disposed at another end of the slow neutron converter; and an anode plate, disposed opposite to the electron multiplier, an electric field being formed between the cathode plate and the anode plate, wherein the slow neutron detector further comprises: a field cage that surrounds the slow neutron converter; and protection rings disposed on both sides of the field cage.

2. The slow neutron detector according to claim 1, wherein the electron multiplier comprises a gas electron multiplier and a micro mesh gaseous chamber.

3. The slow neutron detector according to claim 1, wherein the field cage has a cylindrical structure.

4. The slow neutron detector according to claim 3, wherein the field cage comprises a plurality of coaxial copper rings, the plurality of coaxial copper rings being applied with a gradient voltage respectively.

5. The slow neutron detector according to claim 1, wherein each hole has a circular or polygonal cross-section.

6. The slow neutron detector according to claim 5, wherein each hole has a regular polygonal cross-section.

7. The slow neutron detector according to claim 6, wherein each hole has a regular hexagonal cross-section, and the plurality of holes are evenly arranged, such that the slow neutron converter has a honeycomb structure.

8. The slow neutron detector according to claim 1, wherein each hole has an inscribed circle whose diameter is in the range of 0.1 mm to 20 mm.

9. The slow neutron detector according to claim 8, wherein each hole has an inscribed circle whose diameter is in the range of 3 mm to 10 mm.

10. The slow neutron detector according to claim 1, wherein the substrate has a height in the range of 1 cm to 30 cm along the first direction.

11. The slow neutron detector according to claim 10, wherein the substrate has a height in the range of 10 cm to 15 cm along the first direction.

12. The slow neutron detector according to claim 1, wherein the boron layer contains .sup.natB.

13. The slow neutron detector according to claim 12, wherein the boron layer has a mass thickness in the range of 0.232 to 0.694 mg/cm.sup.2.

14. The slow neutron detector according to claim 12, wherein the boron layer has a mass thickness in the range of 0.3 to 0.4 mg/cm.sup.2.

15. The slow neutron detector according to claim 12, wherein the boron layer has a mass thickness of 0.37 mg/cm.sup.2.

16. The slow neutron detector according to claim 1, wherein the substrate has a cubic or cuboid shape.

17. The slow neutron detector according to claim 1, wherein the insulating walls have a thickness in the range of 1 ?m to ??m.

18. The slow neutron detector according to claim 1, wherein the insulating walls have a thickness in the range of 5 ?m to 20 ?m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, such that the above and other features and advantages will become more apparent.

(2) FIG. 1 is a three-dimensional diagram of a slow neutron converter according to the exemplary embodiment of the present disclosure;

(3) FIG. 2 is a sectional view of the slow neutron converter as illustrated in FIG. 1;

(4) FIG. 3 is a diagram of a relationship between the slow neutron detection efficiency and the mass thickness of a boron layer of the slow neutron converter according to the present disclosure;

(5) FIG. 4 is a schematic structural diagram of a slow neutron detector according to the exemplary embodiment of the present disclosure;

(6) FIG. 5 is a diagram of working principles of the slow neutron detector according to the present disclosure.

DETAILED DESCRIPTION

(7) Exemplary embodiments of the present disclosure are hereinafter described more fully with reference to the accompany drawings. However, the exemplary embodiments may be implemented in a plurality of manners, and shall not be construed as being limited to the implementations described herein. Instead, such exemplary embodiments are provided to more thoroughly and completely illustrate the present disclosure, and fully convey the concepts of the exemplary embodiments to persons skilled in the art. In the drawings, like reference numerals denote like or similar structures or elements. Therefore, repetitive descriptions thereof are not given any further.

(8) In addition, the described characteristics, structures, or features may be incorporated in one or more embodiments in any suitable manner. In the description hereinafter, more details are provided such that sufficient understanding of the embodiments of the present disclosure may be achieved. However, a person skilled in the art would be aware that the technical solutions of the present disclosure may be practiced without one or more of the specific details, or may be practiced using other methods, components, materials, apparatuses, steps or the like. Under other circumstances, commonly known structures, methods, apparatuses, practices, materials or operations are not illustrated or described in detail to avoid various aspects of the present disclosure from becoming ambiguous.

(9) The present disclosure provides a novel detector, wherein a slow neutron converter is fabricated by using a boron layer structure. The detector implements the functions such as slow neutron absorption, ionization of charged particles, electron drift, and then amplifies signals by using an electron multiplier.

(10) FIG. 1 is a three-dimensional diagram of a slow neutron converter according to an exemplary embodiment of the present disclosure. FIG. 2 is a sectional view of the slow neutron converter as illustrated in FIG. 1. It should be understood that the structure schematically illustrated in FIG. 1 and FIG. 2 is merely an example of the slow neutron converter according to the present disclosure. The present disclosure it not limited thereto.

(11) As illustrated in FIG. 1 and FIG. 2, a slow neutron converter 100 according to the present disclosure may include a substrate 120.

(12) The substrate 120 may include a plurality of holes 124 penetrating through the substrate along a first direction, and insulating walls 122 between the plurality of holes.

(13) Each hole 124 may have a circular or polygonal cross-section. According to some embodiments, each hole has a regular polygonal cross-section. According to some embodiments, each hole has a regular hexagonal cross-section, and the plurality of holes are evenly arranged, such that the slow neutron converter has a honeycomb structure, as illustrated in FIG. 1 and FIG. 2, but the present disclosure is not limited thereto. The holes 124 may be filled with an ionization working gas, which would be described in detail hereinafter.

(14) As illustrated in FIG. 2, the slow neutron converter 100 further includes a boron layer 126 at least covering the exposed surface of the plurality of holes 124. According to some embodiments, the boron layer 126 may be made by means of dip-coating or other suitable manners.

(15) The holes 124 may have a smooth exposed surface, such that the boron layer covering the substrate 120 has better uniformity and surface roughness (for example, a flatness of less than 0.1 ?m).

(16) According to the present disclosure, .sup.natB (natural boron) or .sup.10B (purified boron) may be used as a material for slow neutron conversion.

(17) According to some embodiments, the substrate 120 has a cubic or cuboid shape. However, the present disclosure sets no limitation to the specific shape.

(18) According to some embodiments, the insulating walls 122 may have a thickness in the range of 1 ?m to 50 ?m. For example, the insulating walls may have a thickness in the range of 5 ?m to 20 ?m.

(19) According to some embodiments, the insulating walls 122 contain NOMEX paper.

(20) FIG. 3 is a curve diagram of a relationship between the slow neutron detection efficiency and the mass thickness of a boron layer of the slow neutron converter according to the present disclosure.

(21) As illustrated in FIG. 3, if .sup.natB is used as a slow neutron conversion material, when a mass thickness of the boron layer is maintained in the range of 0.232 to 0.694 mg/cm.sup.2 (the corresponding thickness is 1 to 3 ?m when the density is 2.35 g/cm.sup.3), a high slow neutron detection efficiency may be achieved.

(22) According to some embodiments, the boron layer has a mass thickness in the range of 0.232 to 0.694 mg/cm.sup.2. According to some embodiments, the boron layer has a mass thickness in the range of 0.3 to 0.4 mg/cm.sup.2. According to some further embodiments, the boron layer has a mass thickness of 0.37 mg/cm.sup.2.

(23) The present inventors have identified that an over-thin boron layer may cause a reduction in the probability of reaction between the boron layer and slow neutrons, whereas an over-thick boron layer may cause that it is hard for heavy charged particles generated by the reaction to enter into the honeycomb holes from the coating of the converter. The both cases may greatly reduce the overall slow neutron detection efficiency.

(24) In addition, the slow neutron converter needs to have a suitable aperture. According to some embodiments, each hole 124 has an inscribed circle whose diameter is in the range of 0.1 mm to 20 mm. According to some embodiments, each hole 124 has an inscribed circle whose diameter is in the range of 3 mm to 10 mm. In the present disclosure, a hole's inscribed circle refers to a circle that is tangent to most number of sides of the hole.

(25) In addition, the slow neutron converter also needs to have a suitable height, so as to achieve both a higher slow neutron detection efficiency and a better electron migration efficiency. According to some embodiments, the substrate 120 has a height in the range of 1 cm to 30 cm. For example, the substrate 120 may have a height in the range of 10 cm to 15 cm.

(26) According to some embodiments, boron powders in the magnitude of nanometers are uniformly deposited on a NOMEX paper substrate to form a honeycomb structure, and then through cutting and shearing, a slow neutron converter satisfying the requirements in terms of aperture, length and boron layer thickness may be obtained.

(27) FIG. 4 schematically illustrates a structural diagram of a slow neutron detector according to an exemplary embodiment of the present disclosure.

(28) As illustrated in FIG. 4, the slow neutron detector 500 may include a slow neutron converter 520. The slow neutron converter 520 may be a slow neutron converter as described above. The slow neutron detector 500 further includes a cathode plate 510 arranged at one end of the slow neutron converter 520, an electron multiplier 530 arranged at the other end of the slow neutron converter 520, and an anode plate 540 arranged opposite to the electron multiplier 530. An electric field is formed between the cathode plate 510 and the anode plate 520, to drive electrons to drift towards the electron multiplier, which will be described hereinafter.

(29) As described above, the slow neutron converter 520 may include the substrate 120 and the boron layer 126. The plurality of holes 124 of the substrate 120 are filled with an ionization working gas, to produce electrons, which will be described hereinafter. A working gas having a small electron transverse diffusion coefficient may be used, such that the electrons are subjected to less transverse diffusion during the migration process. According to some embodiments, the ionization working gas may be a mixed gas having 95% argon gas and 5% carbon dioxide gas. However, the present disclosure sets no limitation to the working gas, which may be any suitable working gas.

(30) According to some embodiments, the electron multiplier 530 may include a gas electron multiplier, a micro mesh gaseous structure chamber and the like. The electron multiplier is capable of multiplying the quantity of electrons passed, thereby ensuring formation of effective electrical signals.

(31) According to some embodiments, as illustrated in FIG. 4, the slow neutron detector 500 may further include a field cage 550 having a cylindrical structure, wherein the field cage 550 surrounds the slow neutron converter. The field cage 550 may include a plurality of coaxial copper rings, wherein the plurality of coaxial copper rings are respectively applied with a gradient voltage. The field cage 550 may achieve an effect of isolation and shielding, and may restrain equipotential surfaces of an internal gas environment to be parallel in most regions, that is, forming an approximate uniform electric field.

(32) In addition, according to some embodiments, the slow neutron detector 500 may further include protection rings (not illustrated). The protection rings may be arranged on both sides of the field cage, and configured to provide electric levels for planes on both ends, thereby achieving assistance to the formation of the uniform electric field.

(33) FIG. 5 is a diagram illustrating working principles of the slow neutron detector according to the present disclosure. The working principles of the slow neutron detector 500 according to the present disclosure will be described with reference to FIG. 4 and FIG. 5.

(34) As illustrated in FIG. 4 and FIG. 5, the slow neutron detection process according to the present disclosure may be divided into three stages: absorption of slow neutrons to formation of electrons, migration of electrons, multiplication of electrons and signal collection.

(35) A physical process at the stage from absorption of slow neutrons to formation of electrons takes place inside the slow neutron converter. Incident slow neutrons 501 are subjected to a .sup.10B (n, ?) .sup.7Li reaction in the boron layer 126, and heavy charged particles ? and .sup.7Li are produced, the movement directions of which are inverse to each other, and which are evenly distributed within a 4? solid angle. Therefore, in each reaction, at most one particle will enter the gas environment of the honeycomb holes 124. When the ? particles or .sup.7Li particles move into the gas environment inside the holes, energy may be deposited by means of the ionization effect, and thus electrons are produced. If these electrons are detected by a detector, corresponding electrical signals may be formed.

(36) At this stage, the possible slow neutron detection efficiency of the entire detector is determined by both the probability of slow neutrons subjected to the .sup.10B (n, ?) .sup.7Li reaction when the slow neutrons penetrate through the boron layer 126 and the average probability that the ? particles or .sup.7Li particles enter the holes 124. As described above with reference to FIG. 3, when the boron layer has a mass thickness in the range of 0.232 to 0.694 mg/cm.sup.2 (the corresponding thickness is 1 to 3 ?m when the density is 2.35 g/cm.sup.3), a high slow neutron detection efficiency may be achieved.

(37) Due to the ionization effect of the heavy charged particles, initial positions of the produced electrons are distributed inside various honeycomb holes of the entire slow neutron converter. To make these electrons to form output electrical signals, the technical solution according to the present disclosure causes the electrons to migrate out of the holes. As described above, under the electric field, the electrons are driven to drift towards one end of the slow neutron converter, that is, drift towards the electron multiplier 530.

(38) The electron multiplier 530 is capable of multiplying the quantity of electrons passed, thereby ensuring formation of effective electrical signals. A gas electron multiplier (GEM), a micro mesh gaseous structure chamber (micromegas) or other electron multiplier may all cooperate with the slow neutron converter having the boron layer to normally work.

(39) The electrons are collected by the anode plate 540 and thus electrical signals are formed, which is not described herein any further.

(40) Through the above detailed description, a person skilled in the art will easily understand that the system and method according to the embodiments of the present disclosure have one or more of the following advantages.

(41) By using the slow neutron converter having the boron layer according to the present disclosure, a gas slow neutron detector having a good performance may be manufactured.

(42) While maintaining a high slow neutron detection efficiency, the manufacturing complexity and manufacturing cost of the detector are reduced.

(43) Detailed above are exemplary embodiments of the present disclosure. It shall be understood that the present disclosure is not limited to the above exemplary embodiments. Instead, the present disclosure is intended to cover various modifications and equivalent deployments within the spirit and scope of the appended claims.