阅读说明：本技术 一种用于测量高注量率热中子裂变电离室的靶结构 (Target structure for measuring high-fluence thermal neutron fission ionization chamber ) 是由 李立华 莫玉俊 李玮 刘蕴韬 于 2021-07-16 设计创作，主要内容包括：本发明提供一种用于测量高注量率热中子裂变电离室的靶结构,包括铀靶、衬底和效率调节机构,其中所述铀靶包括底衬和位于底衬中间的靶物质,所述衬底的中心设置有贯穿孔；所述衬底沿远离所述贯穿孔的径向依次设置有第一台阶、第二台阶；所述第一台阶用于放置所述铀靶,所述第二台阶用于放置所述效率调节机构；所述效率调节机构的中心设有中间孔,可根据需要调换具有不同中间孔径大小的效率调节机构。本发明通过效率调节机构可减小铀靶靶物质有效半径的大小,进一步降低了裂变电离室的效率。(The invention provides a target structure for measuring a high-fluence thermal neutron fission ionization chamber, which comprises a uranium target, a substrate and an efficiency adjusting mechanism, wherein the uranium target comprises a bottom lining and a target substance positioned in the middle of the bottom lining, and a through hole is formed in the center of the substrate; the substrate is provided with a first step and a second step in sequence along the radial direction far away from the through hole; the first step is used for placing the uranium target, and the second step is used for placing the efficiency adjusting mechanism; the center of the efficiency adjusting mechanism is provided with a middle hole, and the efficiency adjusting mechanisms with different middle hole diameters can be changed as required. The invention can reduce the effective radius of the uranium target material through the efficiency adjusting mechanism, and further reduces the efficiency of the fission ionization chamber.)

1. A target structure for measuring a high-fluence thermal neutron fission ionization chamber is characterized by comprising a uranium target, a substrate and an efficiency adjusting mechanism, wherein the uranium target comprises a bottom lining and a target substance positioned in the middle of the bottom lining, and a through hole is formed in the center of the substrate;

the substrate is provided with a first step and a second step in sequence along the radial direction far away from the through hole;

the first step is used for placing the uranium target, and the second step is used for placing the efficiency adjusting mechanism;

the center of the efficiency adjusting mechanism is provided with a middle hole, and the efficiency adjusting mechanisms with different middle hole diameters can be changed as required.

2. The target structure according to claim 1, wherein the substrate has a thickness of 0.7-0.9 mm.

3. The target structure according to claim 1, wherein the radius of the through-going hole is 16-18 mm.

4. The target structure according to claim 1, wherein the height of the first step is 0.1-0.3 mm.

5. Target structure according to claim 1, characterized in that the radius of the uranium target is 17-19mm and the thickness is 0.2-0.4 mm.

6. The target structure according to claim 1, wherein the height of the second step is 0.45-0.65 mm.

7. The target structure according to claim 1, wherein the radius of the efficiency-adjusting mechanism is 18-20mm and the thickness is 0.15-0.35 mm.

8. The target structure according to claim 1 or 7, wherein the material of the efficiency adjusting mechanism is oxygen-free copper.

9. The target structure of claim 1, wherein the material of the target material is enriched uranium and the material of the backing is platinum.

10. The target structure of claim 1, wherein the substrate is of a material that is oxygen-free copper.

Technical Field

The invention relates to the technical field of nuclear fission measurement, in particular to a target structure for measuring a high-fluence rate thermal neutron fission ionization chamber.

Background

The fission of U-235 induced by neutrons can make fission fragments obtain kinetic energy above 168MeV, meanwhile, the interaction between the heavy charged particles in the fission fragments and the target substance is strong, and when the energy of the heavy charged particles is high, the stopping power of the nuclear electrons of the target substance to the heavy charged particles is expressed as formula (1):

in formula (1):

z-represents the number of charges incident on the particle;

e-basic charge value;

n-number of target atoms per unit volume;

z-the number of nuclei of the target substance;

m₀-free electron mass;

v-incident particle velocity;

i-represents the mean excitation and ionization energy of the atoms of the target substance;

β -represents v/c;

C/Z-represents a shell correction term.

At low energy of the heavy charged particles, the stopping power of the extra-nuclear electrons of the target substance to the heavy charged particles is represented by formula (2):

in formula (2):

a₀-represents the Bohr radius;

v₀-represents the Bohr velocity.

Further, the stopping power of the nuclei of the target substance against the heavy charged particles can be represented by formula (3):

in formula (3):

m₂-nuclear mass representing the target substance;

a-atomic radius of the target substance;

R₀-the closest distance of the incident particle to the nucleus of the target substance.

The formulas (1), (2) and (3) are shown in the references [ atomic nucleus physical experiment method, Wu Zhi Hua, Zhao national Qing, Lu Fu quan, etc. Beijing: atomic energy Press, 1997: 296-.

As can be seen from the formulas (1), (2) and (3), the interaction between the heavy charged particles and the target substance is in a positive relationship with the charge of the heavy charged particles, regardless of whether the energy of the heavy charged particles is high or low, and therefore, the energy deposited by the heavy charged particles in the ionized gas is much greater than the energy deposited by the particles released by the decay of the target substance, regardless of the kinetic energy of the heavy charged particles or the interaction between the heavy charged particles and the target substance; for uranium targets, the energy deposited by the heavy charged particles in the ionized gas is far greater than that deposited by alpha particles (less than 4.8MeV) released by the decay of U isotope and is further greater than that deposited by other background substances, so the U-235 fission ionization chamber is a very good neutron detector.

In a conventional uranium target, uranium is plated on a platinum substrate, as shown in fig. 2 of the accompanying drawings, a small circle part in fig. 2 is uranium, and a large circle part is a platinum substrate.

The characteristic curve of the fission cross section of the neutron and the U-235 is shown in the attached figure 1. In the low energy region, because the fission cross section of the neutron and the U-235 is larger, and because the plating target process is used for plating uranium substances in the central region of the substrate, a collimating hole is made of polytetrafluoroethylene in the center of the substrate in the process, the diameter of the collimating hole is generally more than 1cm in order not to influence the electric field during electroplating, and meanwhile, the effective thickness of the plating target is generally more than 10 mu g/cm². Thus, high fluence (greater than 10) is measured in a U-235 fission ionization chamber⁹cm^-2s^-1) When neutrons are generated, the counting rate is high easily, and the detector is blocked.

Disclosure of Invention

In view of this, the invention aims to design a target structure, which reduces the efficiency of the fission ionization chamber for detecting thermal neutrons, reduces the counting rate of the fission ionization chamber for measuring the thermal neutrons, and avoids the situation of blocking of a detector.

The invention provides a target structure for measuring a high-fluence thermal neutron fission ionization chamber, which comprises a uranium target, a substrate and an efficiency adjusting mechanism, wherein the uranium target comprises a bottom lining and a target substance positioned in the middle of the bottom lining, and a through hole is formed in the center of the substrate;

the substrate is provided with a first step and a second step in sequence along the radial direction far away from the through hole;

the first step is used for placing the uranium target, and the second step is used for placing the efficiency adjusting mechanism;

the center of the efficiency adjusting mechanism is provided with a middle hole, and the efficiency adjusting mechanisms with different middle hole diameters can be changed as required.

Further, the thickness of the substrate is 0.7-0.9 mm;

preferably, the thickness of the substrate is 0.8 mm.

Further, the radius of the through hole is 16-18 mm;

preferably, the through-going hole has a radius of 17 mm.

Further, the height of the first step is 0.1-0.3 mm;

preferably, the height of the first step is 0.2 mm.

Further, the radius of the uranium target is 17-19mm, and the thickness is 0.2-0.4 mm;

preferably, the uranium target has a radius of 18mm and a thickness of 0.3 mm.

Further, the height of the second step is 0.45-0.65 mm;

preferably, the height of the second step is 0.55 mm.

Further, the radius of the efficiency adjusting mechanism is 18-20mm, and the thickness is 0.15-0.35 mm;

preferably, the radius of the efficiency adjustment mechanism is 19mm and the thickness is 0.25 mm.

Further, the material of the efficiency adjusting mechanism is oxygen-free copper.

Further, the material of the target substance is enriched uranium, and the material of the bottom lining is platinum.

Further, the substrate is made of oxygen-free copper.

The effect of the invention is expressed as a multiple of the reduction in efficiency, and the efficiency ratio of the U-235 fission ionization chamber can be expressed as the effective area ratio of the target substance exposed to the ionized gas. The radius of a collimation hole of the traditional uranium target is 12.5mm, the radius of a center hole of the efficiency adjusting mechanism of the target structure is 2.5mm, and the ratio of the efficiency of the fission ionization chamber adopting the traditional uranium target to the efficiency of the target structure is as follows:if the aperture size of the middle hole of the efficiency regulating mechanism is further reduced, such as to 0.5mm of radius, the efficiency of the fission ionization chamber adopting the target structure of the invention is that of the traditional uranium target

Compared with the prior art, the invention has the beneficial effects that:

the invention can reduce the effective radius of the uranium target material through the efficiency adjusting mechanism, and further reduces the efficiency of the fission ionization chamber.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

FIG. 1 is a characteristic plot of neutrons versus a fissile section of U-235;

FIG. 2 is a schematic diagram of the structure of a uranium target of the prior art;

FIG. 3 is a schematic view of a substrate structure according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of an efficiency adjustment mechanism according to an embodiment of the present invention;

fig. 5 is a schematic diagram of the overall structure of a target structure (no uranium target) according to an embodiment of the invention.

In the drawings, the reference numbers denote:

1. a substrate; 11. a through hole; 12. a first step; 13. a second step; 2. a uranium target; 21. a target substance; 22. a bottom lining; 3. an efficiency adjusting mechanism; 31. a middle hole.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

In the description of the present invention, it should be noted that the terms "inside", "outside", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and operate, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the term "connected" is to be interpreted broadly, e.g. as a fixed connection, a detachable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be connected internally or indirectly to each other. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The embodiments of the present invention will be specifically explained with reference to the accompanying drawings:

as shown in fig. 2-5 in particular, the embodiment of the present invention provides a target structure for a fission ionization chamber, including a uranium target 2, a substrate 1 and an efficiency adjusting mechanism 3, where the uranium target 2 includes a bottom liner 22 and a target substance 21 located in the middle of the bottom liner, and a through hole 11 is provided in the center of the substrate 1;

the substrate is sequentially provided with a first step 12 and a second step 13 along the radial direction far away from the through hole;

the first step 12 is used for placing the uranium target 2, and the second step 13 is used for placing the efficiency adjusting mechanism 3;

the center of the efficiency adjusting mechanism 3 is provided with a middle hole 31, the invention can provide a plurality of efficiency adjusting mechanisms with different middle hole diameters, and the efficiency adjusting mechanisms can be replaced according to the requirement, thereby adjusting the size of the middle hole 31 of the efficiency adjusting mechanism.

The thickness of the substrate 1 is 0.7-0.9 mm;

preferably, the thickness of the substrate 1 is 0.8 mm.

The radius of the through hole 11 is 16-18 mm;

preferably, the radius of the through-going hole 11 is 17 mm.

The height of the first step 12 is 0.1-0.3 mm;

preferably, the height of the first step 12 is 0.2 mm.

The radius of the uranium target 2 is 17-19mm, and the thickness is 0.2-0.4 mm;

preferably, the uranium target 2 has a radius of 18mm and a thickness of 0.3 mm.

The height of the second step 13 is 0.45-0.65 mm;

preferably, the height of the second step 13 is 0.55 mm.

The radius of the efficiency adjusting mechanism 3 is 18-20mm, and the thickness is 0.15-0.35 mm;

preferably, the radius of the efficiency adjustment mechanism 3 is 19mm and the thickness is 0.25 mm.

The efficiency adjusting mechanism 3 is made of oxygen-free copper.

The material of the target substance 21 is uranium, and the material of the bottom lining 22 is platinum.

The substrate 1 is made of oxygen-free copper.

The effect of the invention is expressed as a multiple of the reduction in efficiency, and the efficiency ratio of the U-235 fission ionization chamber can be expressed as the effective area ratio of the target substance exposed to the ionized gas. The radius of a collimation hole of the traditional uranium target is 12.5mm, the radius of a center hole of the efficiency adjusting mechanism of the target structure is 2.5mm, and the ratio of the efficiency of the fission ionization chamber adopting the traditional uranium target to the efficiency of the target structure is as follows:if the aperture size of the middle hole of the efficiency regulating mechanism is further reduced, such as to 0.5mm of radius, the efficiency of the fission ionization chamber adopting the target structure of the invention is that of the traditional uranium target

Compared with the prior art, the invention has the beneficial effects that:

the invention can reduce the effective radius of the uranium target material through the efficiency adjusting mechanism, and further reduces the efficiency of the fission ionization chamber.

So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention; various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.