Semiconductor Detector Study for Detecting Fusion Neutrons using Geant4 Simulations
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-05-05 |
| Journal | HNPS Advances in Nuclear Physics |
| Authors | K. Kaperoni, Î. Diakaki, M. Kokkoris, M. Axiotis, Anastasia Ziagkova |
| Institutions | National Centre of Scientific Research âDemokritosâ, National Technical University of Athens |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study utilized GEANT4 simulations to evaluate Silicon (Si), Diamond (C), and Silicon Carbide (SiC) semiconductor detectors for measuring 2.45 MeV fusion neutrons (D-D plasma), focusing on performance in extreme environments like the International Thermonuclear Experimental Reactor (ITER).
- Core Objective: Compare the energy deposition spectra of 50 ”m thick Si, C, and SiC detectors when exposed to 2.45 MeV neutrons, simulating conditions for upcoming ITER D-D plasma tests.
- Material Suitability: Diamond (C) and SiC demonstrated superior performance, exhibiting clear energy deposition thresholds (around 0.4 MeV) enabling effective discrimination between neutron signals and gamma-ray contamination.
- Si Limitation: Silicon (Si) was found to be an inappropriate material for 2.45 MeV neutron detection due to significant spectral overlap between neutron and gamma-ray signals, attributed to its higher atomic number (Z).
- Simulation Methodology: A realistic quasi-monoenergetic neutron beam was modeled using the 3H(p,n) reaction on a TiT target (Ep=3.805 MeV), replicating the setup at the NCSR âDemokritosâ TANDEM accelerator facility.
- Biasing Necessity: Due to the low cross-section of the reactions, two-stage biasing techniques were critical: a factor of 900 for proton-to-neutron production and optimized factors for neutron detection (e.g., factor 100 for C) to achieve high statistical accuracy with minimal deviation (4.12% for C).
- Future Validation: The simulation results are intended to guide the upcoming experimental validation using CIVIDEC detectors at NCSR âDemokritosâ and will inform future studies involving 14 MeV (D-T fusion) neutrons.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target Neutron Energy | 2.45 | MeV | Neutrons produced by D-D fusion plasma |
| Detector Dimensions (Simulated) | 4 x 4 x 50 | mm x mm x ”m | Solid volume detector geometry |
| Incident Proton Energy (Ep) | 3.805 | MeV | Input for 3H(p,n) reaction on TiT target |
| TiT Target Thickness | 0.00057 | cm | Solid target for quasi-monoenergetic neutron production |
| TiT Target Density | 3.75 | g/cm3 | Composition: 42.8% 3H and 57.1% Ti |
| C/SiC Neutron/Gamma Threshold | ~0.4 | MeV | Energy threshold for distinguishing neutron signals from gamma-rays |
| C Detector Biasing Factor | 100 | N/A | Factor used for neutron detection in C (4.12% deviation from unbiased) |
| Si/SiC Minimum Biasing Factor | 2 | N/A | Lowest tested factor for Si/SiC detection (resulting in 11.56% and 7.03% deviation, respectively) |
| ITER Max Neutron Flux (D-T) | Up to 1014 | n/cm2 | Required irradiation resistance for detectors |
| ITER Vacuum Vessel Temperature | 70 to 100 | °C | Standard operating temperature for in-vessel diagnostics |
| ITER Baking Temperature (Tritium Removal) | 200 (Vessel) / 340 (Divertor) | °C | Required survival temperature during shutdown periods |
Key Methodologies
Section titled âKey MethodologiesâThe study relied on the GEANT4 simulation toolkit, employing advanced biasing techniques to ensure statistically robust results for low cross-section nuclear reactions.
- Detector Modeling: C (Diamond), Si, and SiC detectors were modeled as 50 ”m thick solid volumes. The QGSP-BIC physics list was selected to handle hadronic interactions (elastic, inelastic, and capture processes).
- Neutron Source Replication: The experimental setup of the NCSR âDemokritosâ facility was simulated, including the proton beam line, a thin Molybdenum (Mo) entrance foil, the TiT solid target, and a Copper (Cu) beam stop.
- Neutron Production Biasing: A high biasing factor (900) was applied to the primary proton beam within the TiT target volume. This technique increased the probability of the 3H(p,n) reaction occurring, generating a high-statistics quasi-monoenergetic neutron beam (mean energy 2.405 MeV).
- Neutron Detection Biasing: A second stage of biasing was implemented within the detector volume to increase the counting rate of neutron energy deposition events. This was achieved by multiplying the macroscopic cross section (Σt) by a biasing factor, effectively reducing the mean free interaction length (λ).
- Biasing Factor Optimization: Extensive tests were performed to determine the optimal biasing factor for each material that minimized deviation from the unbiased (analogue) simulation case (109 neutrons).
- C required a factor of 100 (4.12% deviation).
- Si and SiC required the lowest tested factor of 2 (due to intense cross-section resonances in Si).
- Gamma-Ray Analysis: Energy deposition spectra were collected for three typical gamma-ray energies (500 keV, 1 MeV, 2 MeV) to assess the materialâs ability to distinguish neutron signals from photon background, confirming the low Z materials (C, SiC) were superior.
Commercial Applications
Section titled âCommercial ApplicationsâThe research directly supports the development and validation of radiation-hardened semiconductor detectors critical for fusion energy and high-radiation environments.
- Fusion Reactor Diagnostics (ITER): Providing validated simulation data for designing neutron flux monitors capable of operating under extreme conditions (high flux, high temperature, strong magnetic fields).
- Radiation-Hardened Sensor Technology: Development of robust detectors based on Diamond and Silicon Carbide, materials known for their high bandgap energy and superior radiation tolerance compared to traditional Silicon.
- High-Flux Neutron Monitoring: Applicable in accelerator facilities, nuclear research reactors, and industrial neutron sources where accurate, high-rate neutron spectroscopy is required.
- Nuclear Physics Research: Validation of GEANT4 biasing techniques for low cross-section reactions, improving the efficiency and accuracy of future simulation studies in experimental nuclear physics.
- High-Temperature Electronics: Utilizing the intrinsic thermal and electrical properties of SiC and Diamond for sensor applications where operational temperatures exceed 100 °C.
View Original Abstract
Accurate neutron flux measurements in fusion reactors are essential, in order to determine the feasibility and progress of the reaction as well as for safety issues. Semiconductor neutron detectors exhibit promising characteristics for operation in the extreme environmental conditions of fusion reactors. Silicon, Diamond and Silicon Carbide are the most studied and anticipated materials for constructing detectors with high efficiency and irradiation resistance. The ITER fusion reactor is expected to run D-D plasma measurements in the near future, so the detection of 2.45 MeV neutrons with appropriate detectors is of great and immediate importance. In the present work the study of 2.45 MeV neutrons interactions with a silicon, diamond and silicon carbide detector was made, using GEANT4 [1] simulations, in order to compare their response. An experimental study will follow at the neutron production facility of the TANDEM accelerator of the I.N.P.P. of the NCSR âDemokritosâ, with detectors provided by CIVIDEC Instrumentation GmbH, so the geometry of the simulations was built accordingly. A quasi-monoenergetic neutron beam of 2.45 MeV was produced through 3H(p,n) reactions in a TiT target. Due to the low cross section of the reaction, biasing techniques were implemented in the simulation to increase the counting rate and thus producing realistic results. These biasing techniques were studied, with various tests and the parameters affecting the choice of the biasing factor are shown and discussed.