A method for analyzing alpha particle energy spectrum in CR-39 solid track detector in mixed radiation field

Abstract

This invention relates to a method for analyzing the energy spectrum of alpha particles in mixed radiation fields using a CR-39 track detector based on step-by-step etching and energy attenuation. The method first etches the CR-39 with a potassium hydroxide-ethanol-water (PEW) solution, utilizing the significant differences in the tracks revealed by protons, alpha particles, and heavy ions to effectively distinguish alpha particles. To address the problem of a narrow energy window for alpha particle track revealing, this invention proposes a novel etching and identification method. By placing a series of energy-degrading sheets of varying thicknesses in front of the CR-39, the wide-spectrum alpha particles are attenuated to the optimal detection range in the spatial dimension. Simultaneously, through multiple step-by-step etching sessions of varying durations, the measurement window is broadened in the temporal dimension, allowing for the acquisition of the alpha particle energy spectrum in a short time, ultimately achieving accurate reconstruction of the alpha particle energy spectrum. This invention achieves high-purity identification and accurate measurement of alpha particles across a wide energy spectrum in complex mixed radiation fields, offering advantages such as low cost, ease of operation, and reliable results.

Description

Technical Field

[0001] This invention relates to the field of nuclear radiation detection technology, specifically to a method for analyzing the energy spectrum of alpha particles in a mixed radiation field of a CR-39 solid track detector. Background Technology

[0002] Solid-state nuclear track detectors (such as CR-39, chemically known as polyallyl diethylene glycol carbonate) have been widely applied in various technological fields, including radiation detection, personal dose monitoring, and space radiation environment research, due to their excellent detection sensitivity to heavily charged particles (such as alpha particles and heavy ions). Their core detection principle is as follows: when charged particles enter the CR-39 material, they cause radiation damage through ionization, forming latent tracks that cannot be directly observed. Subsequent chemical etching (common etching systems include sodium hydroxide aqueous solution and potassium hydroxide-ethanol-aqueous solution) preferentially etches and amplifies the latent tracks, ultimately forming microscopically observable pits, thus enabling particle detection and related parameter analysis.

[0003] To eliminate the influence of a large number of proton signals in the experiment, the industry has proposed a potassium hydroxide-ethanol-water solution (PEW) etching method. By controlling the composition of the etching system and the process conditions, it can significantly increase the linear energy transfer (LET) threshold of track generation, thereby suppressing the manifestation of proton tracks under specific conditions and achieving preliminary screening of alpha particles [Nishiura Y, et al.]. Review of Scientific Instruments

[2019] . However, the PEW etching method still has a key technical shortcoming: the detectable energy range of alpha particles is extremely limited—under fixed etching process parameters, only alpha particles in a specific energy range can form effectively identifiable pits, while alpha particles outside this range (higher or lower energies) cannot be effectively recorded. For example, when the etching time is set to 40 minutes, typically only alpha particles in the 0.6–2.4 MeV energy range can form observable tracks, which greatly limits the method's ability to comprehensively measure a wide range of alpha particles.

[0004] In summary, existing technologies for particle identification and alpha particle energy spectrum analysis in mixed radiation fields have not yet developed a practical solution that combines ease of operation, high detection efficiency, and broad energy spectrum coverage. Therefore, developing a new method capable of effectively identifying particle types and easily and accurately analyzing the alpha particle energy spectrum in mixed radiation fields has become an urgent technical need in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for analyzing the energy spectrum of alpha particles in a mixed radiation field using a CR-39 solid-state track detector based on step-by-step etching and energy decay, comprising the following steps: Step 1: The energy attenuation device is placed in close contact with the front of the CR-39 solid track detector, and both are exposed to a mixed radiation field for irradiation. The energy attenuation device includes a shielding layer and multiple arrayed energy reduction plates. The shielding layer has through holes corresponding to the positions of each energy reduction plate. Each energy reduction plate is spaced apart on the front surface of the shielding layer and covers the through holes. The thickness of each energy reduction plate is different. Step 2: After irradiation, the CR-39 detector is etched in stages using a mixed solution of potassium hydroxide, alcohol, and water (PEW). Step 3: After each etching, based on the differences in the tracks of protons, alpha particles, and heavier ions exhibited by the mixed solution, alpha particle tracks are identified from the mixed tracks by changes in track morphology parameters. The number of alpha particle tracks in the corresponding region of each energy reduction plate is counted. The alpha particle energy spectrum is reconstructed based on the relationship between the number of tracks and the thickness of the energy reduction plate and the pre-calibrated etching time-energy response relationship.

[0006] Furthermore, in step 2, in the mixed solution of potassium hydroxide, alcohol and water, potassium hydroxide accounts for 10%-30% by mass, ethanol accounts for 30%-50% by mass, and the remainder is water, and the etching temperature is 50-75°C.

[0007] Furthermore, in step 2, the number of steps of etching is no less than 2.

[0008] Furthermore, in step 3, image registration technology is used to accurately identify the newly generated α-particle tracks in the same area at different etching stages.

[0009] Furthermore, the number of energy-reducing plates is no less than two.

[0010] Furthermore, the material of the energy-reducing sheet is a light element material that has a known ability to stop alpha particles, such as aluminum, polyimide, or Mylar film.

[0011] Furthermore, in step 3, the identification and statistics of the tracks are completed by an automated optical microscope image analysis system, and the morphological parameters include track diameter, perimeter, area, roundness and grayscale contrast.

[0012] Further, in step 3, the reconstruction of the alpha particle energy spectrum specifically involves converting the measured track number distribution into the energy differential distribution of the alpha particle flux or flux.

[0013] Furthermore, before performing step 1, a pre-calibration step is included: using a standard alpha source, latent tracks of alpha particles with different energies are obtained on the CR-39 detector through energy reduction sheets of different thicknesses; the CR-39 detector is etched in stages; after each etching, the track morphology characteristics of alpha particles with different energies at different etching times are scanned and recorded, and an etching time-energy response relationship database is established. Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) Strong particle discrimination capability: By utilizing the characteristics of PEW etching solution being insensitive to protons and having a larger track size of heavy ions under step-by-step etching, combined with image analysis, the interference of protons and heavy ions in the mixed radiation field can be effectively eliminated, and high-purity extraction of α particles can be achieved.

[0014] (2) Wide energy spectrum measurement capability: It breaks the narrow window limitation of single etching for alpha particle energy measurement, and achieves measurement of multiple energy ranges by using multiple energy reduction plates. (3) Rapid etching capability: It can effectively measure α particles with a wide energy spectrum when the total etching time does not exceed 1 hour. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the assembly structure of the energy attenuation device and the CR-39 detector in an embodiment of the present invention.

[0016] Figure reference numerals: 1-Arrayed energy reduction plates; 2-Shielding layer; 3-CR-39; ①~⑨-Energy reduction plates of different thicknesses.

[0017] Figure 2 This is a graph of the alpha particle energy spectrum measurement window in an embodiment of the present invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation schemes and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0019] I. Pre-calibrated etching time-energy response relationship database Before conducting actual measurements, a database of etching time-energy response relationships needs to be established. The specific method is as follows: use 241An Am standard alpha source (emitting alpha particles with an energy of 5.486 MeV) was used. Aluminum film energy-degrading sheets of varying thicknesses (e.g., 0, 5, 10, 15, 20, 30, 40, 50, 60 μm) were placed sequentially in front of a CR-39 detector to attenuate the alpha particles to different energies, thus obtaining the latent tracks of alpha particles with different energies on the CR-39. The irradiated CR-39 was then etched stepwise under the same etching conditions: a water bath temperature of 50°C, a PEW solution ratio of 15% KOH + 30% C2H5OH + 55% H2O, and etching times of 20 min, 30 min, and 40 min, respectively. After each etching, a microscope equipped with an automated track analysis system was used to scan and record the morphological parameters of the tracks (diameter, roundness, etc.) of alpha particles with different energies at different etching times. This established a database of the correspondence between energy, etching time, and track morphology, i.e., an etching time-energy response database, for alpha particle identification and energy spectrum reconstruction in actual measurements.

[0020] II. Actual Measurement of Alpha Particle Energy Spectrum in Mixed Radiation Field This embodiment uses the measurement of the alpha spectrum generated by laser fusion (such as deuterium-tritium fusion, hydrogen-boron fusion) as an example for illustration.

[0021] 1. Preparation of an energy decay device A multilayer energy attenuation device was fabricated, comprising a shielding layer and multiple arrayed energy reduction plates, each plate being spaced apart on the front surface of the shielding layer and having a different thickness. The shielding layer ensures that alpha particles and other high-energy charged particles can only pass through the energy reduction plate region, reducing background signal interference. This energy attenuation device attenuates alpha particles of different energies to an energy range (e.g., 1-3 MeV) that the CR-39 detector can effectively respond to when the etching time is less than 1 hour.

[0022] This embodiment adopts Figure 1 The diagram shows a nine-grid energy attenuation device. This device includes a 1cm thick stainless steel shielding layer with through-holes corresponding to the positions of each energy-attenuating element; and nine arrayed aluminum film energy-attenuating elements disposed on the front surface of the shielding layer, each covering the through-holes. The nine energy-attenuating elements are spaced apart and have thicknesses of 0, 5, 10, 15, 20, 30, 40, 50, and 60 μm, respectively. A thickness of 0 μm indicates that no energy-attenuating element is placed at that position, and particles directly enter the CR-39 detector through the through-holes. The shielding layer is used to prevent particles from entering the CR-39 detector from the gaps between the energy-attenuating elements.

[0023] The corresponding alpha particle energy detection window is as follows Figure 2 As shown. By setting energy reduction plates of different thicknesses, the broad-spectrum alpha particles are attenuated to within the response window corresponding to each etching time. Combined with step-by-step etching, a complete measurement of the broad-spectrum alpha particles can be achieved.

[0024] 2. Irradiation The energy attenuation device was closely attached to the front of the CR-39 detector and placed together in various directions at a distance of about 50 cm from the target to receive fusion product irradiation.

[0025] 3. Step-by-step etching and track statistics After irradiation, remove the attenuation device and perform step-by-step etching of the CR-39 detector under the following etching conditions: water bath temperature 50°C, PEW solution ratio 15% KOH + 30% C2H5OH + 55% H2O. The etching conditions must be consistent with those used during pre-calibration.

[0026] First etching (T1=20 min): After etching, a microscope equipped with an automatic track analysis system was used to scan the CR-39 region corresponding to each de-energized sheet, and the position and number of all tracks (such as diameter and roundness) that conform to the characteristics of alpha particles at the current etching time were recorded.

[0027] Second etching (T2=30 min): The same CR-39 detector was etched a second time for 30 minutes. After etching, a second scan was performed, and the following two types of tracks were identified using image registration technology: (1) Tracks that appear at time T1 and conform to the characteristics of α particles at time T2, count the number of tracks N1, N2, N3...N9 in each region; (2) Tracks that did not appear at time T1 but appeared after etching at time T2 correspond to α particles with higher energy (not reaching the manifestation threshold at time T1).

[0028] Third etching (T3=40 min): The same CR-39 detector is etched a third time for 40 minutes. After etching, the image is scanned again, and the above identification and statistical process is repeated to record the number of tracks in the corresponding region of each de-energized sheet. If necessary, more etchings (T4, T5, etc.) can be performed, and the above identification and statistical process is repeated after each etching to further broaden the measurement window.

[0029] During the above scanning process, if the tracks that appeared in the previous etchings are found to be significantly larger in a certain scan, or if there are other morphological features that are significantly different from the calibrated tracks, they are excluded from the alpha particles.

[0030] 4. Energy Spectrum Reconstruction Each energy degrader thickness d corresponds to an energy threshold. E d Only when the energy is higher E dOnly alpha particles can penetrate the degrading plate and form tracks on CR-39. Therefore, the number of tracks reflects energies higher than [a certain value]. E d The number of alpha particles was determined. By analyzing the curve N(d) of the track number as a function of the de-energizing plate thickness, and using the stopping power data of alpha particles in the de-energizing plate, the differential energy spectrum of the incident alpha particles was calculated by fitting it with a pre-calibrated etching time-energy response database.

[0031] Those skilled in the art should understand that the energy-degrading sheet material, shielding layer material, etching conditions, etc., described above are merely illustrative examples and are not intended to limit the present invention. For example, the energy-degrading sheet may also be made of other lightweight materials such as polyimide or Mylar film; the shielding layer may also be made of other high-density materials; the etching temperature, time, and solution ratio can be adjusted within the range defined in the claims according to actual needs. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for analyzing the energy spectrum of alpha particles in a mixed radiation field of a CR-39 solid-state track detector, characterized in that, Includes the following steps: Step 1: The energy attenuation device is placed in close contact with the front of the CR-39 solid track detector, and both are exposed to a mixed radiation field for irradiation. The energy attenuation device includes a shielding layer and multiple arrayed energy reduction plates. The shielding layer has through holes corresponding to the positions of each energy reduction plate. Each energy reduction plate is spaced apart on the front surface of the shielding layer and covers the through holes. The thickness of each energy reduction plate is different. Step 2: After irradiation, the CR-39 detector is etched in stages using a mixed solution of potassium hydroxide, alcohol, and water (PEW). Step 3: After each etching, based on the differences in the tracks of protons, alpha particles, and heavier ions exhibited by the mixed solution, alpha particle tracks are identified from the mixed tracks by changes in track morphology parameters. The number of alpha particle tracks in the corresponding region of each energy reduction plate is counted. The alpha particle energy spectrum is reconstructed based on the relationship between the number of tracks and the thickness of the energy reduction plate and the pre-calibrated etching time-energy response relationship.

2. The method according to claim 1, characterized in that, In step 2, the mixed solution of potassium hydroxide, alcohol and water contains 10%-30% potassium hydroxide by mass, 30%-50% ethanol by mass, and the remainder is water. The etching temperature is 50-75°C.

3. The method according to claim 1, characterized in that, In step 2, the number of step-by-step etching operations shall not be less than 2.

4. The method according to claim 1, characterized in that, In step 3, image registration technology is used to accurately identify the newly generated alpha particle tracks in the same area at different etching stages.

5. The method according to claim 1, characterized in that, The number of energy-reducing plates shall not be less than two.

6. The method according to claim 1, characterized in that, The energy-reducing plate is made of a light element material that has a known ability to stop alpha particles.

7. The method according to claim 6, characterized in that, The energy-reducing sheet is made of aluminum, polyimide, or Mylar film.

8. The method according to claim 1, characterized in that, In step 3, the identification and statistics of the tracks are completed by an automated optical microscope image analysis system. The morphological parameters include track diameter, perimeter, area, roundness, and grayscale contrast.

9. The method according to claim 1, characterized in that, In step 3, the reconstruction of the alpha particle energy spectrum specifically involves converting the measured track number distribution into the energy differential distribution of the alpha particle flux or flux.

10. The method according to claim 1, characterized in that, Before performing step 1, a pre-calibration step is also included: using a standard alpha source, the latent tracks of alpha particles with different energies on the CR-39 are obtained through energy reduction sheets of different thicknesses, the CR-39 detector is etched in stages, and the track morphology characteristics of alpha particles with different energies at different etching times are scanned and recorded after each etching, and an etching time-energy response relationship database is established.

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