Measurement of Neutrons Produced by Inertial Fusion with a Diamond Radiation Detector
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-01-25 |
| Journal | Sensors and Materials |
| Authors | Takehiro Shimaoka, Junichi H. Kaneko, Yasunobu Arikawa, Masakatsu Tsubota Mitsutaka Isobe, Kengo Oda |
| Institutions | National Institute of Advanced Industrial Science and Technology, The University of Osaka |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research validates the use of single-crystal Chemical Vapor Deposition (CVD) diamond detectors for critical diagnostics in Inertial Confinement Fusion (ICF) experiments.
- Breakthrough Detection: Successful first-time observation of Deuterium-Deuterium (DD) neutron signals using a single-crystal CVD diamond detector at fluences of 108 neutrons/shot or higher.
- Noise Mitigation: The measurement system employed extensive electromagnetic shielding, electrical floating (using UPS battery power), and optical fiber triggering to overcome strong electromagnetic noise generated by laser irradiation.
- Material Advantage: Single-crystal diamond offers superior charge collection efficiency and, crucially, exhibits no afterpulse or afterglow, solving major limitations faced by plastic scintillators under intense bremsstrahlung X-ray backgrounds (1012-1015 photons/shot).
- Application Validation: The detectorâs fast response successfully discriminated between X-ray and DD neutron signals (6.2 ns time difference), confirming its suitability for neutron Time-of-Flight (ToF) measurements.
- Future Potential: The detector is expected to be effective for measuring neutron bang time and burn history in future fast ignition experiments (FIREX), where neutron yields are projected to reach 1011 neutrons/shot.
- Performance: The detector demonstrated a charge collection efficiency of nearly 100% for both electrons and holes, ensuring high reliability in yield evaluation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material | Single-crystal CVD Diamond | N/A | Homoepitaxially grown |
| Detector Area | 5 x 5 | mm2 | Freestanding film size |
| Detector Thickness | 150 | ”m | Freestanding film thickness |
| Schottky Electrode | Al (3.0 mm diameter, 100 nm thick) | N/A | Fabricated on as-grown surface |
| Ohmic Electrode | TiC/Au (3.0 mm diameter, 100 nm thick) | N/A | Fabricated on substrate side |
| Charge Collection Efficiency | Almost 100 | % | For both electrons and holes |
| Required Time Resolution | Better than 100 | ps | For bang time measurement |
| Required Detector Distance | Within 5.7 | cm | To achieve 100 ps resolution at 5 keV Ti |
| Actual Detector Distance | 14.5 | cm | Used in GEKKO XII experiment |
| Neutron Yield Detected | 108 | neutrons/shot | Minimum yield successfully measured |
| Expected FIREX Yield | 1011 | neutrons/shot | Expected yield for successful fast ignition |
| Neutron Sensitivity | 2 x 10-8 | mV/neutron | Wave height sensitivity for DD neutrons |
| Expected Output Signal (1011 n/shot) | 2 | V | Based on linear scaling of sensitivity |
| Electromagnetic Noise Level | 2 | mV peak-to-peak | Achieved noise level during measurement |
| X-ray / DD Neutron Time Difference | 6.2 | ns | Corresponds to 14.5 cm distance |
| DD Neutron Energy | 2.45 | MeV | Produced by DD reaction |
Key Methodologies
Section titled âKey MethodologiesâThe experiment focused on high-quality sample preparation and rigorous noise mitigation techniques to enable Time-of-Flight (ToF) measurement of DD neutrons generated by the GEKKO XII laser.
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Sample Preparation (CVD Growth):
- Substrate: HP/HT IIa-type substrate with off-angle control.
- Growth Method: Microwave Plasma CVD (System 5250; ASTEX).
- Growth Conditions: Gas pressure of 110 Torr, substrate temperature of 850 °C, microwave power of 1000 W.
- Gas Mixture: CH4/[H2+CH4] concentration of 0.25%.
- Lift-Off: The grown layer was separated by electrolytic etching to obtain a freestanding film (150 ”m thick).
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Detector Fabrication and Characterization:
- Electrodes: Al Schottky electrode (100 nm thick) deposited on the as-grown surface; TiC/Au Ohmic electrode (100 nm thick) deposited on the substrate side.
- Efficiency Check: Charge collection efficiency was confirmed to be almost 100% using alpha-ray-induced charge distribution measurement.
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Noise Reduction and Electrical Floating:
- Shielding: The detector, coaxial cable, and measurement instruments were installed in a metal GS tube and a laboratory-made Cu shielded box.
- Isolation: The detector port was insulated from the target chamber using an acrylic flange. The entire system was electrically floated using UPS battery power to drive instruments.
- Triggering: The trigger signal was transmitted via an optical fiber and photodiode to eliminate electrical noise coupling.
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Neutron Measurement (GEKKO XII):
- Target: Thin 2-3 ”m thick deuterium-gas-filled CD shells were used to maximize neutron generation (108 neutrons/shot).
- Instrumentation: Bias tee (16 GHz bandwidth), oscilloscope (4 GHz bandwidth, 20 GS/s sampling rate) were used for high-speed signal acquisition.
- Confirmation: Neutron signals were confirmed by comparing the output pulse wave height at the expected arrival time (-37 ns) with shots using deuterium-free CH shells (which showed no signal).
Commercial Applications
Section titled âCommercial ApplicationsâThe development of high-speed, radiation-hard single-crystal diamond detectors is critical for applications requiring diagnostics in extreme environments characterized by high neutron flux and intense X-ray backgrounds.
- Fusion Energy Research:
- Neutron bang time and burn history monitoring in ICF facilities (e.g., NIF, GEKKO XII, FIREX).
- Plasma diagnostics requiring high time resolution (less than 100 ps) under intense X-ray loads.
- High-Energy Physics and Accelerators:
- Beam monitoring and dosimetry in high-flux particle accelerators where radiation damage is a concern.
- Time-resolved detection of nuclear reaction products.
- Nuclear Security and Safeguards:
- Fast, radiation-hard neutron detection systems for monitoring nuclear materials and processes.
- High-Power Electronics (Indirectly Related):
- The underlying single-crystal CVD growth technology is essential for producing high-quality diamond substrates used in high-power, high-frequency electronic devices (e.g., 6ccvd.com products like thermal management materials and high-voltage switches).
- Extreme Environment Sensing:
- Sensors operating in environments with high temperatures and intense radiation fields where conventional semiconductor materials fail.
View Original Abstract
We evaluated the neutron bang time in fast-ignition inertial confinement fusion and the response function of deuterium-deuterium (DD) neutrons for burn history monitoring applications with a single-crystal CVD diamond detector.Signals were successfully obtained for the first time with a single-crystal diamond detector for DD neutrons of above 10 8 neutrons/shot.