Simulation Of The Neutron Response Functions Of Diamond Detectors With The Nresp Code

At a Glance

Metadata	Details
Publication Date	2016-10-26
Authors	M. Zbořil, J.E. Guerrero Araque, R. Nolte, A. Zimbal
Citations	6
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Fast Neutron Spectrometry

Executive Summary

Application Validation: Single Crystal CVD (SCD) diamond is confirmed as the superior material for high-resolution spectrometry of fast neutrons, particularly for demanding applications like plasma diagnostics in the ITER fusion project.
Simulation Methodology: The Monte Carlo particle transport code NRESP was successfully adapted and utilized to calculate the neutron response functions (Pulse Height Spectra, PHS) of SCD detectors.
Energy Range Focus: Simulations and benchmarks cover the critical neutron energy range of 7.0 MeV < E_n < 16.0 MeV, essential for fusion reaction analysis.
Reaction Modeling: The NRESP code accurately models complex neutron-induced nuclear reactions in ¹²C, including multi-particle breakup channels (e.g., ¹²C(n,$\alpha$)$^{9}$Be).
Material Requirement: The study underscores the necessity of ultra-high purity SCD material (hydrogen content at ppb level or lower) to ensure accurate simulation and measurement fidelity.
Performance Gap: The research highlights that discrepancies in modeling the low-energy tail of the PHS suggest that charge collection properties—directly related to material quality and defect density—are not yet fully understood or optimized.
6CCVD Value: 6CCVD provides the necessary high-purity, detector-grade SCD material and custom fabrication services (dimensions, metalization) required to replicate and advance this critical research.

Technical Specifications

Parameter	Value	Unit	Context
Detector Material	Single Crystal CVD Diamond	N/A	Optimized for high resolution spectrometry
Experimental Detector Dimensions	4.6 x 4.6 x 0.5	mm³	Used for PHS benchmark measurements
Simulated Neutron Energy Range	7.0 < E_n < 16.0	MeV	Relevant for nuclear fusion plasma diagnostics
Inelastic Scattering Threshold	4.85	MeV	¹²C(n,n’)¹²C* reaction
¹²C(n,$\alpha$)$^{9}$Be Threshold	> 7.2	MeV	Key two-body reaction for neutron spectrometry
Required Material Purity	ppb level	N/A	Hydrogen content set to zero in simulation
Range of 20 MeV Protons in Carbon	1.1 - 1.3	mm	Calculated using SRIM code
Range of 20 MeV Deuterons in Carbon	0.8	mm	Calculated using SRIM code
Range of 20 MeV $\alpha$ Particles in Carbon	0.1	mm	Calculated using SRIM code

Key Methodologies

The simulation and benchmarking process involved adapting the NRESP Monte Carlo code and utilizing high-quality experimental data:

Code Adaptation: The Fortran-based NRESP code, originally developed for liquid scintillation detectors, was modified to simulate neutron-induced reactions occurring specifically within a diamond detector.
Geometry Definition: The simulation geometry was precisely matched to the sensitive volume of the experimental scCVD diamond detector (4.6 x 4.6 x 0.5 mm³).
Purity Modeling: The material was modeled as pure carbon, with hydrogen content set to zero to simulate the ultra-high purity required for detector-grade SCD.
Cross Section Data: Cross sections for neutron-induced reactions in ¹²C were verified against the ENDF/B-VII.1 library.
Angular Distributions: Non-isotropic angular distributions in the center-of-mass system were implemented for key reactions (e.g., ¹²C(n,n)¹²C and ¹²C(n,$\alpha$)$^{9}$Be).
Energy Deposition Model: The nonlinear light output function (used for scintillators) was replaced by a linear relationship between the deposited energy (E_dep) and the resulting pulse height, reflecting the operation of a solid-state diamond detector.
Stopping Power Implementation: Ranges of charged products ($\alpha$ particles, protons, and deuterons) in carbon were calculated using the SRIM code and implemented in a tabulated form within NRESP.
Experimental Benchmark: Simulated PHS were compared against nine experimental PHS measured using quasi-mono-energetic neutron beams (E_n ranging from 7.0 MeV to 16.0 MeV) at the PTB ion accelerator facility (PIAF).

6CCVD Solutions & Capabilities

This research confirms that the successful development of high-resolution neutron spectrometers hinges on the quality and precise fabrication of the Single Crystal Diamond (SCD) material. 6CCVD is uniquely positioned to supply the necessary detector-grade materials and customization services required to replicate and advance this work.

Applicable Materials

To replicate or extend this high-resolution neutron spectrometry research, the following 6CCVD material is required:

Detector Grade Single Crystal Diamond (SCD): Our SCD material is grown via MPCVD with extremely low nitrogen and defect concentrations, ensuring the ultra-high purity (ppb level) necessary for maximizing charge collection distance (CCD) and minimizing background noise, directly addressing the purity requirements of the NRESP simulation.

Customization Potential

The experimental setup utilized a specific detector geometry (4.6 x 4.6 x 0.5 mm³) with circular electrodes. 6CCVD offers comprehensive customization capabilities:

Research Requirement	6CCVD Capability	Technical Benefit
Custom Dimensions: Specific size (4.6 x 4.6 mm) and thickness (0.5 mm) required for accurate response function modeling.	Precision Fabrication: We offer custom plates and wafers up to 125 mm (PCD) and SCD thicknesses from 0.1 µm up to 500 µm, with substrates up to 10 mm. Precision laser cutting ensures exact geometric matching.	Enables precise replication or scaling of detector geometry, critical for matching simulated NRESP response matrices.
Electrode Structure: Circular electrodes used in the benchmark experiment.	Custom Metalization: In-house capability for depositing Au, Pt, Pd, Ti, W, and Cu. We can apply custom electrode patterns (circular, square, or interdigitated) to optimize the internal electric field.	Optimizes charge collection efficiency and uniformity, directly addressing the need for better understanding of charge collection properties noted in the paper’s discussion.
Surface Quality: Ultra-smooth surfaces required for reliable contact deposition and minimizing surface leakage.	High-Quality Polishing: SCD polishing achieves surface roughness (Ra) < 1 nm.	Ensures ideal metal-diamond interfaces, improving detector stability and long-term performance in high-fluence environments.

Engineering Support

The discussion section of the paper highlights that the accurate modeling of the low-energy tail of the PHS requires a better understanding of the charge collection properties of the diamond detector. This is a direct function of the material’s crystalline quality (defect density, trap concentration).

6CCVD’s in-house PhD team specializes in correlating MPCVD growth parameters with resulting electronic properties, such as charge collection distance (CCD) and carrier mobility. We offer expert consultation to assist engineers and scientists in selecting the optimal SCD grade and thickness to maximize charge collection efficiency for similar fast neutron spectrometry projects.

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

View Original Abstract

Detectors based on single crystal synthetic diamond are well suited for high resolution spectrometry of fast neutrons. Their radiation hardness and ability to operate in extreme conditions make them suitable for neutron plasma diagnostics for the ITER project. The task of plasma diagnostics via high resolution neutron spectrometry requires a good knowledge of the response matrix of the detector within a wide energy range. In this work, the Monte Carlo particle transport code NRESP is used for the calculation of the neutron response functions of diamond detectors in the energy range 7 MeV En 16 MeV. The NRESP code, originally developed at the PhysikalischTechnische Bundesanstalt (PTB) for the calculation of the neutron response functions of liquid scintillation detectors, was adapted for the simulation of the neutron-induced reactions which occur in a diamond detector. The simulated response functions are compared to measurements in quasi-mono-energetic neutron beams performed at the PTB ion accelerator facility (PIAF).

Tech Support

Original Source

DOI: https://doi.org/10.22323/1.240.0098