Dose distribution device for plant seed 241Am-9Be source neutron irradiation

Abstract

The invention discloses a 241Am-9Be source dose distribution irradiation device for neutron irradiation of plant seeds. The 241Am-9Be source dose distribution irradiation device mainly comprises a cylindrical shielding body, a transportation plate, a 241Am-9Be neutron source, a spherical shielding layer, a rubber rod and a sample irradiation area, the neutron source generates a large number of 59.5 keV and 4.438 MeV gamma rays during spontaneous fission, the periphery of the neutron source is wrapped with a spherical lead layer to shield the gamma rays, so that the radiation effect on the plant seeds mainly comes from neutron radiation, meanwhile, the geometric center of the neutron source serves as the sphere center, a sample irradiation area is arranged, and the neutron source is subjected to neutron irradiation. The device ensures the uniformity of the absorbed dose of the plant seeds in each area, can be directly given without tedious measurement and calculation, has the characteristic of standardized dose distribution, can meet the scientific research requirements of neutron irradiation of most legume plant seeds, and has a wide application prospect. And the method can be applied to irradiation of other types of plant seeds and neutron radiation agricultural production and mutation breeding.

Description

Technical Field

[0001] The present invention belongs to the technical field of plant seed irradiation breeding, and specifically relates to a method for 241 Am- 9 Dose distribution device for Be source neutron irradiation. Background Art

[0002] Radiation refers to the process in which matter with mass and energy is emitted from a source and continues to propagate outward. With the continuous advancement of science and technology, scientists have designed a variety of radiation devices, which can be used for non-destructive testing and irradiation processing in the industrial field, for radiation disinfection and sterilization, production of radioactive medical isotopes and cancer treatment in the medical field, and for irradiation-induced breeding to improve crop varieties in the agricultural field. Studying the interaction between radiation and living organisms has always been an important direction of scientific research. With the continuous intersection of the fields of life sciences and nuclear sciences, the study of the relative biological effect (RBE) produced by radiation irradiation has received widespread attention. Based on this, the study of the relative biological effect absorbed dose of organisms is crucial. At the same time, the demand for biological irradiation devices, which are essential for studying the relative biological effect, is increasing day by day, and is developing in the direction of miniaturization, directional quantification, and better irradiation uniformity. Therefore, designing a device that can accurately give the relative biological effect absorbed dose of irradiated organisms can promote the development of fields such as biological sciences, medicine, and agriculture, and contribute to human welfare and social progress.

[0003] In the study of radiation-induced mutagenesis and relative biological effects, neutrons have been attracting more and more attention from scientists due to their mutagenic advantages. Neutrons have unique wavelengths and energies, which can penetrate into biological materials and distinguish isotopes (especially hydrogen and deuterium). Compared with X-rays and gamma rays, neutrons have stronger biological effects and higher radiation mutagenesis rates at the same dose. Different rays have different direct or indirect ionization densities when they interact with matter. Even if the sample absorbs the same dose, the relative biological effects caused are different. In order to compare the biological effects caused by different rays, researchers introduced the quality factor. The quality factor of neutrons is dozens of times that of uncharged particles such as X-rays and gamma rays. When the absorbed dose is the same, the total biological effect caused by neutron beams is much greater than that of uncharged particles such as X-rays and gamma rays. In addition, neutrons have a high linear energy transfer density (LET), so their relative biological effect (RBE) is very high, and they are widely used in radiation biological breeding and neutron treatment of cancer.

[0004] In the work of radiation-induced mutagenesis, how to choose the appropriate radiation dose to make plants produce a variety of excellent mutations is the primary issue that radiation-induced mutagenesis breeders need to consider. Generally speaking, as the dose increases, the mutation rate of irradiated plant seeds will also increase accordingly. However, too high a dose may inhibit seed germination, and even if it barely germinates, there is a certain probability that it will die after germination. After radiation treatment, a dose with a plant survival rate of more than 50% and a sterility rate of less than 30% is considered to be an appropriate irradiation dose, which is also called a semi-lethal dose. Therefore, in the actual work of radiation-induced mutagenesis, finding this appropriate dose or semi-lethal dose is an aspect that researchers must pay attention to. However, accurately calculating and directly measuring the dose absorbed by the sample has always been a major challenge in the field of neutron irradiation breeding. At present, there is no exact theoretical formula to predict the neutron absorption dose of samples at different locations. The neutron absorption dose estimation methods commonly used by researchers include Monte Carlo simulation and dose equivalent estimation around the neutron source, which not only consumes a lot of manpower and material resources, but also causes certain errors in the measurement accuracy. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problems of long neutron absorption dose estimation cycle, high cost and poor accuracy in the existing neutron irradiation plant seed research and application process, and to provide a method for plant seed neutron absorption dose estimation. 241 Am- 9 Dose distribution device for Be source neutron irradiation.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A kind of plant seeds 241 Am- 9 A dose distribution device for Be source neutron irradiation, comprising a transport plate and a cylindrical shielding body placed on the transport plate; The inner geometric center of the cylindrical shielding body is provided with 241 Am- 9 Be neutron source, 241 Am- 9 The outer periphery of the Be neutron source is covered with a spherical shielding body composed of a solid source shielding body and a detachable shielding limiter which can be split into two parts in the horizontal direction. The outer periphery of the spherical shielding body is provided with a spherical sample irradiation area which can be split into two parts in the horizontal direction. The sample irradiation area is reserved with a 241 Am- 9 A small hole channel for the Be neutron source to enter and exit; two movable hemispherical cylinders located at the same height as the spherical sample irradiation area are provided on one radial side of the cylindrical shielding body, and one end of the movable hemispherical cylinder extends to 241 Am- 9The Be neutron source is connected to the sample irradiation area, and the other end extends to the outside of the cylindrical shielding body and is connected to the sample changing handle. The other radial side of the cylindrical shielding body is provided with a rubber rod connected to the solid source shielding body and can move freely in the small hole channel of the sample irradiation area. The rubber rod is away from 241 Am- 9 One end of the Be neutron source is connected to one end of a source transfer rod, and one end of the source transfer rod is located outside the cylindrical shielding body and is provided with a source transfer handle; The sample irradiation area is 241 Am- 9 The geometric center of the Be neutron source is the sphere center and the radii increase successively, and the inner surface of each spherical area is provided with a seed sample attachment spherical shell.

[0007] As a further preferred embodiment of the technical solution of the present invention, the irradiation area of ​​the spherical sample is 241 Am- 9 The geometric center of the Be neutron source is the sphere center and the five spherical regions have successively increasing radii, and the inner surface radii of the five spherical regions are 2.65 cm, 3.5 cm, 4.35 cm, 5.2 cm, and 6.05 cm respectively.

[0008] Furthermore, the source transfer rod is composed of a polyethylene rod, a hard lead layer and a stainless steel rod with an arc-shaped free end connected in sequence, and the rubber rod is connected to the arc-shaped end of the stainless steel rod.

[0009] Furthermore, the material composition of the cylindrical shielding body from inside to outside is the same as that of the source shifting rod in the extension direction, which is stainless steel with a diameter of 29.8 cm and a height of 29.8 cm, hard lead with a thickness of 0.1 cm, and polyethylene with a thickness of 3 cm.

[0010] Furthermore, partitions are provided on the upper and lower sides of the rubber rod.

[0011] Furthermore, the 241 Am- 9 The Be neutron source is a cylinder of americium-beryllium alloy.

[0012] Furthermore, the 241 Am- 9 The Be neutron source has a diameter of 1.5 cm and a height of 0.6 cm.

[0013] Furthermore, the seed sample attachment spherical shell is a hard lead spherical shell with a thickness of 1.5 mm.

[0014] Furthermore, the upper surface of the transport plate is provided with a groove matched with the bottom of the cylindrical shielding body.

[0015] Furthermore, universal wheels are provided at the bottom of the transport plate.

[0016] The present invention has the following beneficial effects compared with the prior art: 1. The present invention is used for plant seeds 241 Am- 9 The dose distribution device for Be source neutron irradiation mainly includes a cylindrical shield, a transport plate, 241 Am- 9 Be neutron source, spherical shielding layer, rubber rod and sample irradiation area, 241 Am- 9 The neutron yield of the Be neutron source is 2.2×10 6 n∙s -1 ∙Ci -1 , and a large amount of γ rays will be generated at the same time, with a γ-ray yield of 1.31×10 6 n∙s -1 ∙Ci -1 , which is very close to the neutron yield, needs to be shielded. Therefore, a spherical lead layer (spherical shield) is wrapped around the neutron source to shield the gamma rays, so that the main contribution to the radiation effect on plant seeds comes from neutron radiation, which meets the requirements of neutron irradiation of plant seeds; at the same time, 241 Am- 9 The Be neutron source is the center of the sphere, and five spherical areas with increasing radii are set around the spherical shielding body as sample irradiation areas. The sample irradiation area makes the absorbed dose of plant seeds in each area have good uniformity, and makes the absorbed dose of seeds between the spherical areas have obvious gradients, and makes full use of the limited space resources near the neutron source; in addition, the cylindrical shielding body can reflect part of the neutrons emitted by the neutron source back to the sample irradiation area, making full use of the limited neutron yield. Therefore, the present invention can irradiate seeds of any neutron absorbed dose according to the gradient, and the absorbed dose of seeds in each gradient has good uniformity. This makes the neutron irradiation of plant seeds have the characteristics of standardized dose distribution, which can meet the needs of most scientific research on neutron irradiation of legume seeds and wheat, corn, etc. In addition, it can also be used for neutron radiation agricultural production and mutation breeding.

[0017] 2. The outer material of the cylindrical shield of the present invention is polyethylene. As a common light element, the reaction interface between H and neutrons is large, that is, the probability of H interacting with neutrons such as elastic scattering, inelastic scattering and neutron capture is very high, and it can absorb and slow down neutrons to play a role in radiation protection. Therefore, materials with a high proportion of H elements are often used in the field of radiation protection. Therefore, the applicant selects polyethylene with a high H content as the main material of the cylindrical shield for slowing down and absorbing neutrons. The size and 241 Am- 9The design of the installation position of the Be neutron source enables its radiation protection capability to reach a safe level. At the same time, the present invention opens a small hole channel for the radiation source to enter and exit in the sample irradiation area, and sets a rubber rod that can move freely in the channel. On the one hand, the irradiation area is opened so that the radiation source located at the center of the irradiation area can be guided by the rubber rod to be put in and taken out, which is convenient for the placement and replacement of the radiation source or the sample. On the other hand, the rubber rod is very close to the element composition of the irradiated sample, which can make up for the asymmetry of neutron scattering caused by the lack of material inside the irradiation area after the hole is opened, so it is also ensured that the asymmetric shape after the hole is opened will not have a great influence on the uniformity of the absorbed dose of the seed.

[0018] 3. The top of the transport plate of the present invention has a groove with a radius of 18 cm, on which the cylindrical shielding body can be embedded to reduce shaking. The universal wheels at the bottom can carry the cylindrical shielding body and move flexibly, which is easy to use.

[0019] 4. The raw materials required for the present invention are lead, hard lead, stainless steel and polyethylene, which are cheap, easy to obtain, easy to make and inexpensive. 241 Am- 9 Be neutron sources are also relatively easy to obtain. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of a cylindrical shielding body of the present invention; Figure 2 for Figure 1 A longitudinal section view of Figure 3 A schematic diagram of the side surface of the transport plate of the present invention; Figure 4 It is a schematic cross-sectional view of the whole device of the present invention; Figure 5 For the present invention 241 Am- 9 A partial enlarged view of the Be neutron source and the sample irradiation area; Figure 6 It is a partial enlarged view of the source transfer rod of the present invention; The meanings of the reference numerals are as follows: 1. cylindrical shielding body; 2. sample changing handle; 3. 241 Am- 9 Be neutron source; 4. Sample irradiation area; 5. Movable hemispherical cylinder; 6. Removable shielding limiter; 7. Seed sample attachment spherical shell; 8. Rubber rod; 9. Partition; 10. Transport board; 11. Universal wheel; 12. Source transfer handle; 13. Solid source shielding body; 14. Stainless steel rod; 15. Hard lead layer; 16. Polyethylene rod. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] like Figure 1-6 As shown, a method for neutron irradiation of plant seeds 241 Am- 9 The Be source dose distribution irradiation device comprises a cylindrical shielding body 1 and a transport plate 10. The top of the transport plate 10 has a groove with a radius of 18 cm for placing the cylindrical shielding body 1. The bottom of the transport plate 10 is provided with four universal wheels 11 for easy movement of the device. The cylindrical shielding body 1 has a diameter of 36 cm and a height of 36 cm. 241 Am- 9 Be neutron source 3, 241 Am- 9 The outer periphery of the Be neutron source 3 is covered with a lead spherical shielding body with a diameter of 5 cm, which is composed of a solid source shielding body 13 and a detachable shielding limiter 6 that can be split into two parts in the horizontal direction. The outer periphery of the spherical shielding body is provided with a spherical sample irradiation area 4 that can be split into two parts in the horizontal direction. The sample irradiation area 4 is reserved with a 241 Am- 9 The Be neutron source 3 enters and exits the small hole channel; the cylindrical shield 1 is provided with two movable hemispherical cylinders 5 at the same height as the spherical sample irradiation area 4 on the radial right side of the inner side, and the movable hemispherical cylinders 5 have a diameter of 6.9 cm and a height of 18 cm, and one end of the movable hemispherical cylinders 5 extends to 241 Am- 9 The other end of the Be neutron source 3 extends to the outside of the cylindrical shield 1 and is connected to the sample change handle 2. The cylindrical shield 1 is provided with a rubber rod 8 connected to the solid source shield 13 and can move freely in the small hole channel of the sample irradiation area 4. The rubber rod 8 is a cylinder with a diameter of 2 cm. The rubber rod 8 is away from the sample irradiation area 4. 241 Am- 9 One end of the Be neutron source 3 is connected to one end of a source transfer rod, and a source transfer handle 12 is provided at one end of the source transfer rod located outside the cylindrical shielding body 1 .

[0023] Specifically, 241 Am- 9 The Be neutron source 3 is an americium-beryllium alloy cylinder with a diameter of 1.5 cm and a height of 0.6 cm. It is an isotope neutron source with a neutron yield of 2.2×10 6 n∙s -1 ∙Ci -1 , half-life is 432.2a, 241 Am- 9 The average energy of neutrons from the Be neutron source is 4.5 MeV. When it undergoes spontaneous fission, it will also produce a large number of 59.5 keV and 4.438 MeV gamma rays, of which the gamma ray yield is 1.31×10 6 n∙s -1 ∙Ci -1, the sample irradiation zone 4 is 241 Am- 9 The geometric center of the Be neutron source 3 is the center of the sphere and there are five spherical areas with increasing radii. The inner surface radii of the five spherical areas are 2.65 cm, 3.5 cm, 4.35 cm, 5.2 cm, and 6.05 cm respectively. The inner surface of the spherical area is provided with a hard lead seed sample attachment spherical shell 7 with a seed sample attachment thickness of 1.5 mm.

[0024] Specifically, the source transfer rod is composed of a polyethylene rod 16, a hard lead layer 15 and a stainless steel rod 14 with an arc-shaped free end connected in sequence, and the rubber rod 8 is connected to the arc-shaped end of the stainless steel rod 14.

[0025] Specifically, the material composition of the cylindrical shielding body 13 from inside to outside is the same as that of the source shifting rod in the extending direction, namely, stainless steel with a diameter of 29.8 cm and a height of 29.8 cm, hard lead with a thickness of 0.1 cm, and polyethylene with a thickness of 3 cm.

[0026] Specifically, hard lead partitions 9 with a thickness of 1.5 mm are provided on the upper and lower sides of the rubber rod 8 .

[0027] Before each irradiation, the sample irradiation area 4 is first pulled out through the sample changing handle 2 installed on the movable hemispherical cylinder 5, and the plant seeds are filled into the five seed sample attached spherical shells 7 through the opening at the back of the split body and filled up, and then they are sealed with tape and pushed into the cylindrical shielding body 1 as they are. After irradiation, the sample irradiation area 4 is pulled out again, the tape is removed, the sample is removed and replaced, and this process is repeated. 241 Am- 9 When the Be neutron source 3) is moved, the source moving handle 12 installed on the left side of the device is pulled to drive the source moving rod and the rubber rod 8 connected thereto, thereby driving the solid source shielding body 13 connected to the rubber rod 8 to move, thereby driving 241 Am- 9 The Be neutron source 3 performs the required shift.

[0028] The absorbed dose rates of the five spherical areas of the sample irradiation area 4 are given by simulation technology for different types of plant seeds. The acquisition process is as follows: 241 Am- 9 On the basis of the Be neutron source model, according to the energy spectrum data of neutrons and gamma rays, the neutron kerma factor and the mass energy absorption coefficient of rays, it is simulated and calculated based on the Monte Carlo method.

[0029] Table 1 shows the neutron absorption dose rates of pea seeds in the five spherical areas of the device when the activity of the radiation source is 10Ci.

[0030] Table 1 Neutron absorbed dose rates in five spherical regions Table 2 shows the relative errors of neutron absorbed dose rates of pea seeds in the five spherical regions of the device.

[0031] Table 2 Relative errors of neutron absorbed dose rates in five spherical regions A human tissue equivalent point was placed at 50cm from the top and side of the device to conduct Monte Carlo simulation of the absorbed dose rate, simulating the neutron and gamma-ray absorbed doses that the human body may receive when changing samples, to test radiation safety issues. The results showed that without placing any irradiated samples, the neutron absorbed dose rates at 50cm from the top and side were 8.79μSv / h and 9.95μSv / h, respectively, and the gamma-ray absorbed dose rates were 0.13μSv / h and 0.14μSv / h, respectively. According to GB18871-2002 "Ionizing Radiation Protection and Radiation Source Safety Standards", the radiation standards for human safety are: the annual average effective dose for 5 consecutive years (but no retrospective average can be made) ≤20mSv; the effective dose in any year ≤50mSv; the annual equivalent dose of the eye lens ≤150mSv; the annual equivalent dose of the limbs (hands and feet) or skin ≤500mSv. Considering the characteristics and usage of this device, this standard can be met during operation and it is safe and harmless to the human body when used at a safe distance.

Claims

1. A kind of plant seeds 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: It comprises a transport plate (10), and a cylindrical shielding body (1) placed on the transport plate (10); The cylindrical shielding body (1) has a 241 Am- 9 Be neutron source (3), 241 Am- 9 The Be neutron source (3) is coated with a spherical shielding body composed of a solid source shielding body (13) and a detachable shielding stopper (6) which can be split into two parts in a horizontal direction. The spherical shielding body is provided with a spherical sample irradiation area (4) which can be split into two parts in a horizontal direction. The sample irradiation area (4) has a reserved area for 241 Am- 9 A small hole channel for the Be neutron source (3) to enter and exit; two movable hemispherical cylinders (5) located at the same height as the spherical sample irradiation area (4) are provided on one side of the inner radial direction of the cylindrical shielding body (1), and one end of the movable hemispherical cylinder (5) extends to 241 Am- 9 The Be neutron source (3) is connected to the sample irradiation zone (4), and the other end extends to the outside of the cylindrical shield (1) and is connected to the sample change handle (2). The cylindrical shield (1) is provided with a rubber rod (8) on the other side of the inner radial direction, which is connected to the solid source shield (13) and can move freely in the small hole channel of the sample irradiation zone (4). The rubber rod (8) is away from 241 Am- 9 One end of the Be neutron source (3) is connected to one end of a source transfer rod, and one end of the source transfer rod is located outside the cylindrical shielding body (1) and is provided with a source transfer handle (12); The sample irradiation zone (4) is 241 Am- 9 The Be neutron source (3) is composed of a plurality of spherical regions whose geometric center is the sphere center and whose radii increase successively, and the inner surface of each spherical region is provided with a seed sample attachment spherical shell (7).

2. A method for plant seeds according to claim 1 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: The spherical sample irradiation area (4) is 241 Am- 9 The Be neutron source (3) is composed of five spherical regions with the geometric center being the sphere center and the radii increasing successively, and the inner surface radii of the five spherical regions are 2.65 cm, 3.5 cm, 4.35 cm, 5.2 cm, and 6.05 cm successively.

3. A method for plant seeds according to claim 2 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: The source transfer rod is composed of a polyethylene rod (16), a hard lead layer (15) and a stainless steel rod (14) with an arc-shaped free end, which are connected in sequence, and the rubber rod (8) is connected to the arc-shaped end of the stainless steel rod (14).

4. A method for plant seeds according to claim 3 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: The material composition of the cylindrical shielding body (13) from inside to outside is the same as that of the source transfer rod in the extension direction, namely, stainless steel with a diameter of 29.8 cm and a height of 29.8 cm, hard lead with a thickness of 0.1 cm, and polyethylene with a thickness of 3 cm.

5. A method for plant seeds according to claim 3 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: The rubber rod (8) is provided with partitions (9) on the upper and lower sides.

6. A method for plant seeds according to claim 1 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: Said 241 Am- 9 The Be neutron source is a cylinder of americium-beryllium alloy.

7. A method for plant seeds according to claim 6. 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: Said 241 Am- 9 The Be neutron source has a diameter of 1.5 cm and a height of 0.6 cm.

8. A method for plant seeds according to any one of claims 1 to 7. 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: The seed sample attachment spherical shell (7) is a hard lead spherical shell with a thickness of 1.5 mm.

9. A method for plant seeds according to any one of claims 1 to 7. 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: The upper surface of the transport plate (10) is provided with a groove which matches the bottom of the cylindrical shielding body (1).

10. A method for plant seeds according to any one of claims 1 to 7 241 Am- 9 The dose distribution device for Be source neutron irradiation is characterized in that: The bottom of the transport plate (10) is provided with a universal wheel (11).

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