Test of Diamond sCVD Detectors at High Flux of Fast Neutrons

At a Glance

Metadata	Details
Publication Date	2025-08-07
Journal	Particles
Authors	L. Weissman, A. Shor, Sergey Vaintraub
Institutions	Soreq Nuclear Research Center, Israel Atomic Energy Commission
Analysis	Full AI Review Included

Executive Summary

Core Achievement: Single-crystal Chemical Vapor-Deposited (sCVD) diamond detectors were successfully tested and validated for simultaneous spectroscopic and timing measurements under extremely high fast neutron flux conditions.
High Flux Performance: The detectors maintained stable operation and provided meaningful spectroscopic data at neutron flux densities up to 10¹⁰ n/s/cm² (14 MeV neutrons), a rate significantly higher than previously reported for spectroscopic diamond tests.
Spectroscopic Resolution: Excellent energy resolution was confirmed using alpha sources, achieving 13 keV (FWHM) for 5.5 MeV alpha particles with a standard spectroscopic amplifier (1.2 µs shaping time).
Timing Capabilities: Waveform analysis confirmed the fast rise time of the signals, supporting the potential for sub-nanosecond time resolution required for future Time-of-Flight (TOF) facilities.
Operational Limitations: Testing with the pulsed neutron generator (ING-031) introduced strong electronic noise and baseline modulation, limiting the achievable energy resolution quality compared to DC sources.
Primary Application: The detectors are proposed for use at the SARAF Phase II facility as high-rate neutron flux monitors and as active targets for measuring critical nuclear cross-sections, such as the ¹²C(n,n’)3α reaction.

Technical Specifications

Parameter	Value	Unit	Context
Detector Type	Single-crystal CVD (sCVD) B3	N/A	Cividec detectors
Detector Dimensions	140 µm thick, 10 mm²	N/A	Sensitive volume
Detector Bias Voltage	+120	V	Alpha source tests
Dark Leakage Current	Few	nA	Alpha source tests
Alpha Energy Resolution (Spectroscopic)	13	keV (FWHM)	For 5.5 MeV alpha (1.2 µs shaping)
Alpha Energy Resolution (Fast)	~35	keV	For 5.5 MeV alpha (10 ns shaping)
Fast Neutron Flux Density (Stable Operation)	Up to 10¹⁰	n/s/cm²	Achieved stable operation (25 cm distance)
Peak Neutron Rate (Pulse)	6.6 x 10¹³	n/s	During 0.5 µs pulse duration
Neutron Energy	14	MeV	Generated via t(d,n) reaction
Neutron Generator Yield (Average)	~10⁸	n/s (4π)	ING-031 average yield
Amplifier Shaping Time (Fast)	10	ns	C6 fast spectroscopic amplifier
Detector Dead Layer	100	nm	Titanium electrode
Radiation Hardness (Reported)	10	MGy	Superior radiation tolerance

Key Methodologies

Detector Configuration: Two 140 µm thick sCVD diamond detectors were tested in a vacuum chamber (3 x 10^-5 mbar) at a bias of +120 V.
Signal Amplification: Signals were processed using both fast (C6, 10 ns shaping) and spectroscopic (CX-L, 1.2 µs shaping) amplifiers to evaluate timing and energy resolution capabilities.
Data Acquisition: A high-speed digitizer (Acqiris_U5303A, 1.6 GHz sampling rate) was used to record waveforms event-by-event, allowing for post-analysis of energy spectra and pulse shape.
Source Calibration: Energy calibration was performed using a standard triple alpha source (²³⁹Pu, ²⁴¹Am, ²⁴⁴Cm). The response to heavy ions was checked using a ²⁵²Cf fission source, confirming the known pulse-height defect for heavy fragments.
Neutron Irradiation: Tests utilized an ING-031 pulsed neutron generator (14 MeV, 30 Hz frequency). Detectors were placed at 5 cm (high pileup) and 25 cm (resolved events) from the source.
Noise Mitigation: Attempts were made to reduce electronic noise associated with the generator pulse (e.g., ground rearrangement, metallic foil shielding, insulating transformer), but the noise persisted.
Modeling and Simulation: GEANT4 Monte-Carlo simulations (version 4.11.0.0, NRESP71 model) were performed to understand neutron interaction channels (elastic, inelastic, ¹²C(n,n’)3α) and predict Time-of-Flight (TOF) vs. deposited energy correlations.

Commercial Applications

Fusion Energy Diagnostics: Used as robust, radiation-hard neutron spectrometers and flux monitors in high-intensity environments like fusion reactors (e.g., validating performance beyond previously tested fluxes of 10⁹ n/s/cm²).
Accelerator Physics (TOF Tagging): Deployment as fast timing counters (sub-nanosecond resolution potential) for neutron energy tagging in Time-of-Flight facilities, especially under high instantaneous flux during short beam pulses.
High-Rate Neutron Monitoring: Reliable, long-term monitoring of fast neutron flux density (up to 10¹⁰ n/s/cm²) in the vicinity of powerful accelerator targets (e.g., SARAF Phase II).
Nuclear Astrophysics Research: Utilizing the diamond detector as an active target to measure critical cross-sections, such as the ¹²C(n,n’)3α reaction, which is relevant to stellar carbon synthesis.
Homeland Security/Industrial Neutron Sources: Applications requiring highly radiation-hard detectors capable of operating reliably in pulsed, high-dose neutron fields where conventional semiconductor detectors would quickly degrade.

View Original Abstract

We have tested the performance of spectroscopic single-crystal Chemical Vapor-Deposited (sCVD) diamond detectors with radioactive sources and with a pulsed deuterium-tritium neutron generator. The tests demonstrate that the detectors could provide good timing and spectroscopic information at high neutron fluxes. The spectroscopic information can be obtained at a 14 MeV neutron rate as high as 1010 n/cm2/s, despite some limitations associated with pulse character of the used neutron generator. Monte-Carlo simulations were performed in order to achieve better understanding of neutron interaction with the detector material. Possible applications for the use of the detectors at Soreq Applied Research Accelerator Facility (SARAF) are considered. The detectors could be used as reliable neutron rate monitors in the vicinity of a strong accelerator-based source of energetic neutrons. The detectors could also be utilized as time-of-flight tagging counters in nuclear physics experiments under condition of high neutron fluxes during short beam pulses. In particular, measurement of the 12C(n,n′)3α cross-section is discussed.

Tech Support

Original Source

DOI: https://doi.org/10.3390/particles8030075

References

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