A multi-activation foil and method for measuring neutron energy spectrum

Abstract

The application relates to the technical field of neutron measurement, and particularly discloses a multi-activation foil for measuring a neutron energy spectrum and a method. The multi-activation foil comprises a shell and activation sheets arranged in the shell, and the activation sheets sequentially comprise Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe from top to bottom. The activation foil can realize high-resolution measurement of the neutron energy spectrum in a very small space, has the characteristics of miniaturization, wide energy response range, wide neutron flux rate adaptation range, controllable manufacturing tolerance, optimized material ratio and the like, is suitable for neutron energy spectrum and neutron dose measurement of a small-scale area of a nuclear facility, and can be popularized and applied to fine dose field distribution measurement of a large-scale area of the nuclear facility, so as to provide accurate data support for safe operation, shielding verification and radiation protection of the nuclear facility.

Description

Technical Field

[0001] This invention relates to the field of neutron measurement technology, and specifically discloses a multi-activated foil and method for measuring neutron energy spectra. Background Technology

[0002] In nuclear reactor operation, safety assessment, shielding design, and radiation protection, accurate acquisition of neutron spectrum information is a crucial foundation. Neutron spectrum not only directly affects the accuracy of reactor physics calculations but also provides input parameters for the design and optimization of shielding structures. By measuring the neutron spectrum, neutron flux and dose rate distribution can be obtained, allowing for feedback and correction of shielding calculation models and improving the reliability of radiation field predictions. Furthermore, neutron spectrum information can be used to estimate fuel burnup, the irradiation history of specific isotopes, assess material irradiation damage, and even provide a basis for reconstructing post-accident personnel radiation dose. In advanced nuclear energy systems such as fusion reactors, neutron spectrum is a core tool for diagnosing plasma performance, neutron yield, and energy distribution.

[0003] However, in small nuclear facilities (such as small modular reactors (SMRs), microreactors, compact research facilities, or fusion experimental reactors), due to the highly compact equipment layout and limited space, the neutron radiation field can change significantly within the centimeter or even millimeter scale, forming a strong spatial gradient. Traditional neutron spectroscopy methods, such as long counters and liquid scintillator detectors, are often bulky or lack sufficient spatial resolution, making it difficult to achieve multi-point, high-resolution spectral measurements within a limited space. Furthermore, conventional activated foil assemblies typically consist of multiple independent foils, occupying a large space, and are prone to measurement errors in strong gradient fields due to detector position uncertainties.

[0004] Activated foil method, a classic neutron energy spectrum measurement technique, utilizes materials with different neutron reaction thresholds and the variation of their activation reaction cross-section with neutron energy, combined with deconvolution algorithms, to infer the neutron energy spectrum. However, existing activated foil systems have several limitations when applied to complex small-scale radiation fields: First, the combined size of multiple activated foils is large, making dense deployment in confined spaces difficult; second, traditional combination methods lack integrated design, leading to spatial positioning difficulties; third, most activated foil materials have limited response ranges, making it difficult to cover a wide energy range from thermal neutrons to fast neutrons; finally, some materials are prone to saturation at high flux rates, while their sensitivity is insufficient and dynamic range is limited at low flux rates. Current technologies lack systematic consideration for the standardization, miniaturization, and multi-material integrated design of activated foils, making it difficult to meet the demands of modern small nuclear facilities for high spatial resolution, wide energy response, and large dynamic range neutron measurements. Summary of the Invention

[0005] This invention provides a multi-activated foil and method for measuring neutron energy spectrum. The activated foil has the advantages of wide measurement neutron energy spectrum (covering 0.0253eV-20MeV), wide applicable neutron flux range, and small detector size, enabling high-resolution measurement of neutron energy spectrum in a very small space.

[0006] This invention is achieved through the following technical solution: On one hand, the present invention provides a multi-activated foil for measuring neutron energy spectrum, comprising a shell and activated sheets placed inside the shell. The activated sheets, from top to bottom, are composed of Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe. The dimensions of the activated sheets of Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe are Φ17.4mm×1mm, Φ17.4mm×1mm, Φ17.4mm×0.36mm, Φ17.4mm×1mm, Φ17.4mm×1mm, Φ17.4mm×2mm, Φ17.4mm×0.6mm, Φ17.4mm×2mm and Φ17.4mm×1mm, respectively.

[0007] In this invention, the shell is an Al shell, which is a cylinder with an open top and a hollow interior.

[0008] In this invention, the outer diameter of the Al shell is 20mm, the inner diameter is 18mm, the wall thickness is 1mm, and the bottom thickness is 1mm.

[0009] In this invention, the diameter tolerance of the bottom surface of the Al shell is 0.12 mm, the height tolerance is 0.1 mm, and the tolerances for bottom thickness and wall thickness are 0.05 mm.

[0010] In this invention, the radial tolerance of the activated sheet is 0.1 mm, and the height tolerance is 0.05 mm.

[0011] In this invention, the purity of the activated sheet materials Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe is not less than 99.9%.

[0012] In this invention, the proportions of each nuclide in the activated sheet material Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe are the natural abundances.

[0013] On the other hand, the present invention provides a method for measuring neutron energy spectrum, employing the above-mentioned multi-activated foil for measuring neutron energy spectrum, comprising the following steps: 1) The prepared multi-activated foil matrix is ​​loaded into an irradiation fixture and placed in a specific location of the nuclear facility for irradiation; 2) After irradiation, the multi-activated foil was removed, and the mononuclear activation rate was measured based on the dose rate level on the surface of the activated foil; 3) Based on the measurement results and the known neutron energy response function, the neutron energy spectrum at the measurement location is solved using neutron spectrum analysis software.

[0014] In this invention, in step 2): If the surface dose rate is below 0.5 μSv / h, conduct experimental measurements. If the target nuclide count reaches 1000, stop the measurement. If the target nuclide count is less than 1000, the measurement time is fixed at 3 hours.

[0015] The technical solution of the present invention has at least the following advantages and beneficial effects: (1) The overall size is Φ20mm×12mm, which is greatly reduced to the centimeter level. Compared with the existing online neutron spectrometer, the size is reduced by an order of magnitude. It is particularly suitable for measurement in narrow spaces and large neutron gradients, and is also suitable for neutron energy spectrum measurement in large-scale spaces.

[0016] (2) The multi-activated foil is made of materials that are sensitive to thermal neutrons, medium-energy neutrons and fast neutrons. It has a wide neutron energy response range, covering thermal neutrons from 0.0253eV to 20MeV. It is significantly different from the typical multi-activated foil used for BNCT (neutron energy response range 0.5eV-10keV), the typical multi-activated foil used for DT neutron source measurement with moderator (neutron energy response range 10eV-20MeV), and the typical multi-activated foil used for Cf-252 neutron source measurement (neutron energy response range 1eV-20MeV). The neutron energy response range of this invention is wider and it is suitable for neutron energy spectrum measurement of various nuclear facilities such as fission reactors, fusion reactors and medical accelerators.

[0017] (3) Through simulation calculations, the irradiation time, activation foil thickness, and placement sequence were designed to achieve a wide range of neutron flux rates for the multi-electrode foil, with an applicable range of 7.75 × 10⁻⁶. 4 -3.22×10 10 n / (cm 2 It can accurately measure the neutron energy spectrum, especially at high neutron flux density, and is comparable to typical multi-activated foils used for BNCT (applicable neutron flux measurement range greater than or equal to 5.0 × 10⁻⁶ ppm). 8 n / (cm 2 ·s), a typical multi-activated foil used for measurements at the DT neutron source and Cf-252 neutron source (neutron flux measurement range 1). 10 6 -1 10 7 n / (cm 2 ·s), a typical multi-activated foil used for spallation neutron source measurements (neutron flux measurement range should be greater than 1×10).10 n / (cm 2 ·s), a typical multi-activated foil for fast neutron pulse reactor measurements (neutron flux measurement range should be greater than 2.77 × 10⁻⁶). 9 n / (cm 2 There are significant differences between the two (·s).

[0018] (4) The activated foil of the present invention can realize high-resolution measurement of neutron energy spectrum and neutron dose in a very small space. It has the characteristics of miniaturization, wide energy response range and wide neutron flux rate adaptability. It solves the problem of insufficient measurement accuracy of neutron radiation field in small-scale space. It is not only suitable for the measurement of neutron energy spectrum and neutron dose in small-scale areas of nuclear facilities, but can also be extended to the measurement of fine dose field distribution in large-scale areas of nuclear facilities, providing accurate data support for the safe operation, shielding verification and radiation protection of nuclear facilities. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of the multi-activated foil for measuring neutron energy spectrum provided by the present invention; Figure 2 A top view of the multi-activated foil for measuring neutron energy spectrum provided by the present invention; Figure 3 A front view of the multi-activated foil for measuring neutron energy spectrum provided by the present invention; Figure 4 Provided by the present invention Figure 3 Sectional view at point AA.

[0020] Reference numerals: 1-Ni, 2-Sc, 3-Au, 4-W, 5-Cu, 6-Pt, 7-In, 8-Zn, 9-Fe, 10-Al shell. Detailed Implementation

[0021] The following is a detailed description of the implementation method in conjunction with the accompanying drawings.

[0022] Example 1 Reference Figures 1-4 This embodiment provides a multi-activated foil for measuring neutron energy spectrum, including a shell and activation sheets placed inside the shell. The activation sheets, from top to bottom, include Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe. The dimensions of the Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe activation sheets are Φ17.4mm×1mm, Φ17.4mm×1mm, Φ17.4mm×0.36mm, Φ17.4mm×1mm, Φ17.4mm×1mm, Φ17.4mm×2mm, Φ17.4mm×0.6mm, Φ17.4mm×2mm and Φ17.4mm×1mm, respectively.

[0023] In this invention, the shell is an Al shell, which is a cylinder with an open top and a hollow interior.

[0024] In this invention, the outer diameter of the Al shell is 20mm, the inner diameter is 18mm, the wall thickness is 1mm, and the bottom thickness is 1mm.

[0025] In this invention, the diameter tolerance of the bottom surface of the Al shell is 0.12 mm, the height tolerance is 0.1 mm, and the tolerances for bottom thickness and wall thickness are 0.05 mm.

[0026] In this invention, the radial tolerance of the activated sheet is 0.1 mm, and the height tolerance is 0.05 mm.

[0027] In this invention, the purity of the activated sheet materials Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe is not less than 99.9%.

[0028] In this invention, the proportions of each nuclide in the activated sheet material Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe are the natural abundances.

[0029] A method for measuring neutron energy spectra, employing the aforementioned multi-activated foil for measuring neutron energy spectra, includes the following steps: 1) The prepared multi-activated foil matrix is ​​loaded into an irradiation fixture and placed in a specific location of the nuclear facility for irradiation; 2) After irradiation, remove the multi-activated foil and measure the mononuclear activation rate based on the surface dose rate level of the activated foil. If the surface dose rate is below 0.5 μSv / h, continue the experiment; if the target nuclide count reaches 1000, stop the measurement; if the target nuclide count is below 1000, fix the measurement time to 3 hours. The main measurement steps are as follows: 2-1) Background measurement: Background measurement should be performed before or after detection as needed, and the background spectrum should be saved. If a significant full-energy peak of an artificial radionuclide appears in the background, the detector or lead chamber should be checked for contamination, and if so, it should be removed in time.

[0030] 2-2) Sample Measurement: Open the lead chamber door and place the sample to be measured on the detector inside the lead chamber. The detection position and geometric conditions should be consistent with those during efficiency calibration. Press the shortcut key "Alt+1" or the "Go" button in the toolbar to start the measurement. After the measurement is completed, click "File" → "Save As" in the menu to save the corresponding spectral file to the computer. Before the next round of measurement or when a remeasurement is required, press the key "Alt+3" or the clear screen button in the toolbar to clear the screen.

[0031] 2-3) Nuclide analysis: retrieve the sample spectrum and background spectrum to be analyzed, select the nuclide library file and the corresponding calibration file of the sample, and perform qualitative and quantitative analysis on the sample after subtracting the background spectrum.

[0032] 2-4) Calculate the mononuclear activation rate of the target nuclide in the activated sample according to the following formula: (1) In the formula: R i —Mononuclear activation rate of the target nuclide in the activated sample; N—Net peak area of ​​the full-energy peak measured in the sample; t c —Sample measurement time, seconds; F1—the decay correction factor for short-lived nuclides during the measurement period, calculated using equation (2). If the half-life of the nuclide being analyzed is greater than 100 compared to the time of the sample measurement, F1 can be set to 1. F2—γ conformation additive correction factor. For nuclides emitting monoenergetic γ-rays, or when the corresponding correction factor for the estimated γ-rays being analyzed is not large, F2 can be taken as 1; otherwise, F2 should be estimated. E—Detection efficiency of the full-energy gamma-ray peak at the corresponding energy; m—mass of the sample, in grams; M—molar mass of the nuclide to be activated in the sample, g / mol; w—mass percentage of the nuclide to be activated in the activated sample; N A —Avogadro's constant; e—natural constant; η—the branching ratio of gamma-ray emission at the corresponding energy; λ—decay constant of a radionuclide, s -1 ; Δt—Nucleotide decay time, which is the time interval between the sampling time and the sample measurement time, in seconds.

[0033] (2) In the formula: F1—decay correction factor for short-lived nuclides during the measurement period. If the half-life of the nuclide being analyzed is greater than 100 compared with the time of sample measurement, F1 can be taken as 1. λ—decay constant of a radionuclide, s -1 ; T c — is the time of sample measurement (i.e., the actual time of sample measurement), in seconds; e—natural constant.

[0034] 3) Based on the measurement results and the known neutron energy response function, the neutron energy spectrum at the measurement location is solved using neutron spectrum analysis software.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-activated foil for measuring neutron energy spectra, characterized in that, The device includes a housing and activation sheets placed inside the housing. The activation sheets, from top to bottom, consist of Ni, Sc, Au, W, Cu, Pt, In, Zn, and Fe. The dimensions of the activation sheets for Ni, Sc, Au, W, Cu, Pt, In, Zn, and Fe are Φ17.4mm×1mm, Φ17.4mm×1mm, Φ17.4mm×0.36mm, Φ17.4mm×1mm, Φ17.4mm×1mm, Φ17.4mm×2mm, Φ17.4mm×0.6mm, Φ17.4mm×2mm, and Φ17.4mm×1mm, respectively.

2. The multi-activated foil for measuring neutron energy spectra according to claim 1, characterized in that, The shell is an Al shell, which is a cylinder with an open top and a hollow interior.

3. The multi-activated foil for measuring neutron energy spectra according to claim 2, characterized in that, The Al shell has an outer diameter of 20mm, an inner diameter of 18mm, a wall thickness of 1mm, and a bottom thickness of 1mm.

4. The multi-activated foil for measuring neutron energy spectra according to claim 2 or 3, characterized in that, The tolerance for the bottom diameter of the Al shell is 0.12 mm, the tolerance for the height is 0.1 mm, and the tolerances for the bottom thickness and wall thickness are 0.05 mm.

5. The multi-activated foil for measuring neutron energy spectra according to claim 1, characterized in that, The radial tolerance of the activated sheet is 0.1 mm, and the height tolerance is 0.05 mm.

6. The multi-activated foil for measuring neutron energy spectra according to claim 1, characterized in that, The purity of the activated sheet materials Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe is not less than 99.9%.

7. The multi-activated foil for measuring neutron energy spectra according to claim 1, characterized in that, The proportions of each nuclide in the activated sheet material Ni, Sc, Au, W, Cu, Pt, In, Zn and Fe are at their natural abundance.

8. A method for measuring the neutron energy spectrum, characterized in that, The method of measuring neutron energy spectrum using the multi-activated foil according to any one of claims 1-7 includes the following steps: 1) The prepared multi-activated foil matrix is ​​loaded into an irradiation fixture and placed in a specific location of the nuclear facility for irradiation; 2) After irradiation, the multi-activated foil was removed, and the mononuclear activation rate was measured based on the dose rate on the surface of the activated foil; 3) Based on the measurement results and the known neutron energy response function, the neutron energy spectrum at the measurement location is solved using neutron spectrum analysis software.

9. The method according to claim 8, characterized in that, In step 2): If the surface dose rate is below 0.5 μSv / h, conduct experimental measurements. If the target nuclide count reaches 1000, stop the measurement. If the target nuclide count is less than 1000, the measurement time is fixed at 3 hours.

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