Simultaneous measurement of energy spectrum and fluence of neutrons using a diamond detector
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-07-14 |
| Journal | Scientific Reports |
| Authors | Jie Liu, Haoyu Jiang, Zengqi Cui, Yiwei Hu, Haofan Bai |
| Institutions | Peking University, State Key Laboratory of Nuclear Physics and Technology |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details the first successful realization of simultaneous measurement of neutron energy spectrum and absolute fluence using a single Chemical Vapor Deposition (CVD) diamond detector.
- Core Achievement: Simultaneous determination of neutron energy spectrum and absolute fluence was achieved by deconvolving the measured pulse height spectrum using a systematically derived absolute response matrix.
- Material Advantage: CVD diamond detectors were selected for their outstanding radiation hardness and high-temperature endurance, making them uniquely suitable for intense neutron fields in fusion devices (e.g., ITER, EAST).
- Response Matrix Generation: A comprehensive absolute response matrix (1.0 to 20.0 MeV) was generated using a self-developed Monte Carlo simulation code, incorporating ten critical neutron-induced reactions on 12C and 13C.
- Validation (d-d Neutrons): Measurements of d-d neutrons (5.0 to 10.5 MeV) showed excellent consistency in main-energy fluence when compared against the 238U fission chamber reference. Spectral results matched those obtained using an EJ-309 liquid scintillator.
- Validation (d-t Neutrons): The detector successfully measured the spectrum and fluence of 14.2 MeV d-t neutrons, with fluence results consistent with the associated alpha particle method.
- Methodology: The GRAVEL iterative unfolding method was applied to the pulse height spectra using the simulated absolute response matrix.
- Future Work: Accuracy of spectral and fluence measurements depends heavily on the precision of nuclear reaction data used in the simulation, necessitating further measurements and evaluations of carbon reaction data, especially at higher neutron energies.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material | Natural Diamond (CVD) | N/A | Selected for radiation hardness and high-temperature endurance. |
| Detector Dimensions | 4.0 x 4.0 x 0.5 | mm3 | Volume used in Monte Carlo simulation. |
| Neutron Energy Range (Simulated) | 1.0 to 20.0 | MeV | Absolute response matrix generated with 0.1 MeV intervals. |
| Energy Resolution Correction | 4 | % | Applied during simulation of deposited energy. |
| Simulation Incident Neutrons | 4 x 106 | N/A | Number of neutrons simulated per response function. |
| Simulation Fluence Normalization | 2.5 x 107 | n/cm2 | Used to calculate the absolute response function. |
| d-d Neutron Energies Tested | 5.0, 5.5, 8.5, 9.5, 10.5 | MeV | Measured using Van de Graaff and HI-13 tandem accelerators. |
| d-t Neutron Energy Tested | 14.2 | MeV | Measured using Cockcroft-Walton generator (300 keV deuteron beam). |
| Main-Energy Fluence (5.0 MeV, Diamond) | 3.21 x 107 | n/cm2 | Compared to 238U fission chamber reference (3.17 ± 0.11 x 107 n/cm2). |
| Main-Energy Fluence (14.2 MeV, Diamond) | 3.75 x 108 | n/cm2 | Compared to associated alpha particle reference (3.62 ± 0.18 x 108 n/cm2). |
| Low-Energy Neutron Proportion (5.0 MeV, Diamond) | 14.6 | % | Compared to EJ-309 liquid scintillator (16.8%). |
| Low-Energy Neutron Proportion (10.5 MeV, Diamond) | 51.2 | % | Compared to EJ-309 liquid scintillator (38.5%). |
Key Methodologies
Section titled âKey MethodologiesâThe simultaneous measurement relies on a highly detailed Monte Carlo simulation to generate the absolute response matrix, followed by experimental validation and data unfolding.
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Response Matrix Simulation (Monte Carlo Method):
- Code Development: A self-developed code realized with MATLAB was used for the Monte Carlo simulation.
- Reaction Inclusion: Ten nuclear reaction channels (seven for 12C, three for 13C) were included, covering elastic, inelastic, and multi-body reactions (e.g., 12C(n, n+3α)).
- Nuclear Data Sourcing: Data libraries (ENDF/B-VIII.0, CENDL-3.2, JEFF-3.3) and calculated data (TALYS-1.9 code) were used for cross sections, angular differential cross sections (two-body reactions), and double differential cross sections (multi-body reactions).
- Particle Tracking: Neutrons were tracked in 1.0 ”m steps. Charged secondary particles were tracked in 0.01 MeV energy steps until their energy was less than 0.01 MeV or they escaped the 4.0 x 4.0 x 0.5 mm3 diamond volume.
- Normalization: Response functions were generated from 4 x 106 incident neutrons and normalized by the simulated fluence (2.5 x 107 n/cm2) to yield the absolute response matrix.
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Experimental Setup (d-d and d-t Sources):
- d-d Source Setup: Experiments used a deuterium gas target. Detectors included the diamond detector, an EJ-309 liquid scintillator, and a 238U fission chamber for reference measurements.
- d-t Source Setup: Experiments used a solid tritium-titanium (T-Ti) target (1.0 mg/cm2 thickness). The diamond detector was placed 193 cm from the target at 80° relative to the deuteron beam.
- Signal Acquisition: The diamond detector utilized a CIVIDEC fast charge amplifier C6, with signals recorded by a commercial CAEN DT5730 digitizer (10 bit, 500 MHz).
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Data Unfolding:
- Method: The GRAVEL iterative unfolding method was applied to the measured pulse height spectra.
- Output: The unfolding process simultaneously yielded both the neutron energy spectrum and the absolute neutron fluence, based on the simulated absolute response matrix.
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated capability of simultaneous neutron spectrum and fluence measurement using CVD diamond detectors is highly valuable for applications requiring robust, high-precision neutron diagnostics in extreme environments.
- Fusion Reactor Diagnostics (ITER, EAST):
- Neutron Yield Monitoring: Providing accurate, absolute fluence measurements essential for determining fusion power output.
- Plasma Physics: Delivering high-resolution energy spectra necessary for diagnosing ion temperatures and other critical plasma parameters in high-flux, high-temperature environments where traditional detectors fail.
- Nuclear Research and Development:
- Accelerator Facilities: Monitoring intense neutron fields generated by high-power accelerators used for materials testing or isotope production.
- Nuclear Data Measurement: Utilizing the diamond detector as an active target to precisely measure cross sections of neutron-induced reactions on carbon, improving fundamental nuclear data libraries (ENDF/B, JEFF).
- Advanced Dosimetry:
- High-Flux Dosimetry: Developing compact, fast-response detectors capable of simultaneous spectral and fluence measurements for improved radiation protection and safety in nuclear facilities.
- High-Temperature Sensing:
- Leveraging the diamond materialâs intrinsic high-temperature endurance (up to 1000 °C) for neutron monitoring in hot sections of advanced fission or fusion reactors.