Measurement of Neutrons Produced by Inertial Fusion with a Diamond Radiation Detector

At a Glance

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	The University of Osaka, Hokkaido University
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Single-Crystal CVD Diamond for ICF Neutron Diagnostics

This document analyzes the research paper “Measurement of Neutrons Produced by Inertial Fusion with a Diamond Radiation Detector” and outlines how 6CCVD’s specialized Microwave Plasma CVD (MPCVD) diamond materials and fabrication services can support and advance this critical research area.

Executive Summary

The research successfully demonstrated the use of a Single-Crystal Diamond (SCD) detector for monitoring Deuterium-Deuterium (DD) neutron production in fast-ignition Inertial Confinement Fusion (ICF) experiments.

Core Achievement: First successful detection of DD neutron signals (2.45 MeV) using an SCD detector at yields above 10⁸ neutrons/shot.
Material Superiority: SCD was chosen over Polycrystalline Diamond (PCD) due to its superior charge collection efficiency (CCE) and lack of afterpulse, crucial for operation under intense X-ray/bremsstrahlung noise (up to 10¹⁵ photons/shot).
Performance Metrics: The detector achieved an almost 100% CCE for both electrons and holes, validating the high quality of the homoepitaxial CVD growth.
Application: The detector is confirmed suitable for measuring neutron bang time and burn history, requiring a time resolution better than 100 ps.
Noise Mitigation: Successful signal acquisition required extensive electromagnetic shielding, electrical floating of the system, and optical fiber triggering to overcome 2 mV peak-to-peak noise.
Future Scaling: Achieving the target neutron yield (10¹¹ neutrons/shot) in future FIREX experiments is expected to produce a 2 V output signal, confirming the viability of SCD for high-gain fusion diagnostics.

Technical Specifications

Parameter	Value	Unit	Context
Detector Material	Single-Crystal Diamond (SCD)	N/A	Homoepitaxially grown CVD
Detector Area	5 x 5	mm²	Freestanding film
Detector Thickness	150	µm	Lifted off by electrolytic etching
Schottky Electrode Material	Aluminum (Al)	N/A	Resistance heating deposition
Ohmic Electrode Material	TiC/Au	N/A	Electron beam deposition
Electrode Diameter	3.0	mm	Both Schottky and Ohmic
Electrode Thickness	100	nm	Both Schottky and Ohmic
Neutron Type Measured	DD Neutrons	N/A	2.45 MeV energy
Minimum Detected Yield	10⁸	neutrons/shot	First successful SCD detection
Required Time Resolution	< 100	ps	For 5 keV ion temperature measurement
Measured Neutron Sensitivity	2 x 10^-8	mV/neutron	In terms of wave height
Measured EM Noise Level	2	mV	Peak-to-peak (after shielding)
Expected Future Signal (10¹¹ yield)	2	V	Projected output signal
Charge Collection Efficiency (CCE)	Almost 100	%	Evaluated via alpha-ray measurement

Key Methodologies

The single-crystal diamond detector was fabricated using advanced MPCVD techniques and precise metalization processes:

Substrate Preparation: An off-angle-controlled High Pressure/High Temperature (HP/HT) IIa-type substrate was used for homoepitaxial growth.
MPCVD Growth: A Microwave Plasma CVD system (ASTEX 5250) was utilized under the following conditions:
- Gas Pressure: 110 Torr
- Substrate Temperature: 850 °C
- Microwave Power: 1000 W
- Methane Concentration (CH₄/[H₂+CH₄]): 0.25%
Film Separation: The grown SCD layer was lifted off the substrate using electrolytic etching to obtain a freestanding film 150 µm thick.
Schottky Contact Fabrication: A 100 nm thick Aluminum (Al) electrode (Φ3.0 mm) was fabricated on the as-grown surface via resistance heating deposition.
Ohmic Contact Fabrication: A 100 nm thick TiC/Au electrode (Φ3.0 mm) was fabricated on the substrate side surface via electron beam deposition.
Performance Validation: The detector’s charge collection efficiency was confirmed to be nearly 100% using alpha-ray induced charge distribution measurement.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-purity, custom-fabricated SCD materials required for next-generation ICF diagnostics, enabling researchers to replicate and scale the results achieved in this paper.

Applicable Materials

The success of this research hinges on the high quality and purity of the SCD material, which minimizes charge trapping and eliminates afterpulse effects common in PCD under high X-ray flux.

Material Requirement	6CCVD Solution	Technical Advantage
High-Purity SCD	Optical Grade Single Crystal Diamond (SCD)	Ultra-low defect density ensures near 100% Charge Collection Efficiency (CCE) and eliminates afterpulse, critical for high-speed, high-noise environments.
Freestanding Film	Custom SCD Plates (0.1 µm to 500 µm)	We supply SCD films in the required 150 µm thickness, ready for lift-off or provided as freestanding plates, simplifying detector fabrication.
Future High-Flux Needs	Heavy Boron-Doped Diamond (BDD)	For applications requiring enhanced conductivity or specialized neutron conversion layers, 6CCVD offers BDD films up to 500 µm thick.

Customization Potential

The paper utilized specific dimensions (5 x 5 mm²) and a custom metal stack (Al/TiC/Au). 6CCVD’s in-house fabrication capabilities directly address these needs:

Custom Dimensions: While the paper used 5 x 5 mm², 6CCVD can supply SCD plates up to 500 µm thick and PCD wafers up to 125 mm in diameter, allowing for increased detector area to boost neutron sensitivity (as recommended in the conclusion).
Advanced Metalization: The required Al (Schottky) and TiC/Au (Ohmic) contacts are fully supported. 6CCVD offers internal metalization services including Au, Pt, Pd, Ti, W, and Cu stacks, deposited via electron beam or sputtering, ensuring optimal ohmic and Schottky performance for high-voltage applications.
Surface Finish: To ensure optimal contact and performance, 6CCVD guarantees ultra-smooth surfaces with polishing down to Ra < 1 nm for SCD, exceeding standard requirements for detector fabrication.
Global Logistics: 6CCVD provides reliable global shipping (DDU default, DDP available), ensuring prompt delivery of custom materials to international research facilities like those involved in the GEKKO XII and FIREX projects.

Engineering Support

6CCVD’s in-house PhD team specializes in optimizing MPCVD growth recipes and material selection for extreme radiation environments. We can assist researchers in scaling up the detector design for the 10¹¹ neutrons/shot yield target by:

Material Optimization: Consulting on the optimal SCD thickness and crystal orientation to maximize neutron interaction cross-section while maintaining fast response time.
Electrode Design: Assisting with the design and fabrication of custom metal stacks and geometries to minimize electromagnetic noise pickup and improve high-frequency signal integrity (up to 16 GHz bandwidth required in the experiment).
Process Replication: Providing materials grown under tightly controlled conditions, similar to the 110 Torr, 850 °C, and 0.25% CH₄ concentration parameters cited, ensuring high reproducibility for critical ICF diagnostics projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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.

Tech Support

Original Source

DOI: https://doi.org/10.18494/sam4671