Selective data analysis for diamond detectors in neutron fields

At a Glance

Metadata	Details
Publication Date	2017-01-01
Journal	EPJ Web of Conferences
Authors	C. Weiß, H. Frais-Kölbl, E. Griesmayer, P. Kavrigin
Institutions	CIVIDEC Instrumentation (Austria), Fachhochschule Wiener Neustadt
Citations	1
Analysis	Full AI Review Included

Selective Data Analysis in MPCVD Diamond Detectors for Neutron Applications: 6CCVD Technical Brief

This technical brief analyzes the requirements and achievements detailed in “Selective data analysis for diamond detectors in neutron fields” (Weiss et al., 2017) and aligns them with the advanced capabilities of 6CCVD’s specialized MPCVD diamond materials and processing services.

Executive Summary

This research validates the use of high-electronic grade Single Crystal Diamond (SCD) detectors coupled with Transient Current Technique (TCT) analysis for superior particle discrimination in demanding neutron environments, driving the requirement for ultra-high purity diamond material.

Superior Particle Discrimination: The intrinsic electronic properties of SCD allow for the identification and separation of incident particles (neutrons, $\gamma$-rays, heavy ions) based on subtle differences in the induced signal shape (rectangular vs. triangular).
Background Rejection: Signal shape analysis successfully suppressed high background contamination (e.g., proton recoils and $\gamma$-flux) that conventionally masks critical neutron reaction spectra in both thermal and fast fields.
High Purity Requirement: Replication and advancement of this technique necessitates high electronic grade MPCVD SCD with extremely low impurity levels, specifically < 5 ppb Nitrogen (N) and < 0.03 ppb Nitrogen-Vacancy (NV) centers, to maintain intrinsic detector signal quality.
Quantifiable Success: In fast neutron cross-section measurements (e.g., ${}^{13}$C(n,$\alpha$)${}^{10}$Be), background rejection reached 99.95% efficiency, enabling previously inaccessible spectroscopic analysis.
Technical Focus: Key parameters for particle identification include Full Width at Half Maximum (FWHM), base width ($w_{b}$), and the derived Form Factor ($F$), which compare calculated vs. measured signal area ($F = (h \cdot w_{b}) / A$).
6CCVD Value: 6CCVD provides the necessary ultra-high purity, custom-thick SCD wafers, coupled with in-house metalization capabilities, essential for manufacturing optimized TCT detectors.

Technical Specifications

The following table extracts critical hard data points and material requirements necessary for the function and performance of TCT-based diamond detectors described in the paper.

Parameter	Value	Unit	Context
Required N Concentration	< 5	ppb	Necessary for high electronic grade SCVD
Required NV Center Conc.	< 0.03	ppb	To avoid deterioration of intrinsic signal
Typical Sensor Thickness ($d$)	500	µm	Used in reported thermal and mixed-field experiments
Typical Applied E-Field	1	V/µm	Standard operating condition for drift analysis
Electron Drift Velocity ($v_{d,e-}$)	6.0 $\pm$ 0.1	10${}^{4}$ m/s	Measured at 1 V/µm E-field
Hole Drift Velocity ($v_{d,h+}$)	8.5 $\pm$ 0.2	10${}^{4}$ m/s	Measured at 1 V/µm E-field
Ballistic Center Drift Time ($t_{d,bc}$)	Shortest possible	ns	Narrowest signal base width
Max Signal Interaction Rate	10	MHz	Capability of required real-time analysis system
FWHM (Anode Ionization)	6	ns	Narrowest signal (e${}^{-}$ drift dominated) for 500 µm sensor
FWHM (Cathode Ionization)	9	ns	Widest signal ($h$$^{+}$ drift dominated) for 500 µm sensor
Background Rejection Achieved	99.95	%	Rejection of proton recoils in fast neutron beam

Key Methodologies

The core of the presented technique relies on the careful preparation and analysis of high-quality SCD material signals using TCT.

Material Selection: Use of high-electronic grade SCD (< 5 ppb N) to maximize carrier mobility and minimize trapping, ensuring the measured signal reflects the intrinsic ionization current.
Ionization and Charge Generation: Incident particles (e.g., $\alpha$-particles, protons, or MIPs) ionize the diamond lattice, creating free electron ($e^{-}$) and hole ($h^{+}$) charge carrier pairs.
Bias Field Application: A bias voltage is applied across the diamond thickness ($d$), creating an electric field (up to 1 V/µm) to induce free charge carrier drift to the respective electrodes.
TCT Signal Acquisition: The drifting charges induce a current ($I$) in the external circuit (Shockley-Ramo theorem). This requires specialized 50 $\Omega$ systems, 2 GHz broadband amplifiers, and low-capacitance detectors to capture the fast (nanosecond-scale) timing properties.
Signal Shape Analysis (SSA): Analysis focuses on extracted parameters:
- Amplitude ($h$): Height of the signal.
- Area ($A$): Proportional to the deposited energy.
- Width Parameters ($w_{b}$ / FWHM): Indicate the duration of charge drift, which is highly dependent on the location of the ionization (e.g., ballistic center vs. near-electrode).
Particle Identification via Form Factor ($F$): Calculating the ratio $F = (h \cdot w_{b}) / A$. This distinguishes particle types based on the resultant signal shape: $F \approx 1$ for rectangular signals (heavy ions, point-like ionization) and $F \approx 2$ for triangular signals (MIPs, $\gamma$-rays, homogeneous ionization).

6CCVD Solutions & Capabilities

6CCVD is an industry leader in manufacturing the advanced MPCVD diamond materials required to replicate and extend the sophisticated neutron detection research presented in this paper.

Requirement from Paper	6CCVD Capability & Solution	Engineering Advantage
High-Electronic Grade Material (N < 5 ppb, NV < 0.03 ppb)	Optical Grade Single Crystal Diamond (SCD) wafers are grown specifically for superior electronic performance and high carrier mobility, meeting the stringent purity requirements for TCT detectors.	Enables intrinsic signal retention, critical for distinguishing particle interactions based on drift time analysis (TCT/SSA).
Custom Thickness & Dimensions (500 µm typical)	SCD Material: Thickness control from 0.1 µm up to 500 µm. Substrate Material: Available up to 10 mm thick for high-energy applications. Dimensions: Plates/wafers up to 125 mm (PCD).	Precise thickness optimization is essential as drift time and FWHM are directly proportional to sensor thickness ($d$).
Detector Polishing/Surface Quality (For robust metallization)	Ultra-High Polishing: Guaranteed Ra < 1 nm for SCD material.	Excellent surface finish ensures optimal deposition of electrodes, reducing contact resistance and surface scattering noise critical for high-speed GHz TCT electronics.
Electrode Fabrication (Bias field application)	Internal Metalization Services: Capabilities for high-quality electrode deposition, including Au, Pt, Pd, Ti, W, and Cu layers.	Allows engineers to define custom contact geometries (e.g., coplanar, interdigitated, Schottky contacts) necessary for creating ohmic contacts and optimized electric field uniformity required for accurate drift measurements.
Advanced Research Support (Replication/Extension)	In-House PhD Engineering Team: 6CCVD offers consultation on material parameters (purity, doping, thickness, metal scheme) to optimize sensors for neutron detection, high-flux environments, and TCT analysis.	Accelerates R&D cycles by ensuring immediate access to materials perfectly matched to specific nuclear reactor or plasma diagnostic requirements.

Applicable Materials

To replicate the core findings of this research, 6CCVD recommends:

Optical Grade SCD: Essential for achieving the ultra-low impurity levels (< 5 ppb N) required for high spectroscopic performance and low charge trapping necessary for TCT measurements in neutron fields.
Custom Thickness SCD Wafers: Tailored from 100 µm to 500 µm, depending on the specific application (thermal neutron conversion layers vs. fast neutron intrinsic detection).

Customization Potential

6CCVD provides end-to-end customization to fit exacting experimental requirements, including:

Custom Dimensions and Shaping: Wafers can be provided up to 125 mm, or laser-cut to smaller, precise geometries for detector arrays or in-core deployment.
Custom Metal Layer Stacks: Fabrication of precise Ti/Pt/Au or other multi-layer contacts tailored for robust performance in high radiation and temperature environments.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection, geometry optimization, and contact scheme design for projects focused on Transient Current Technique (TCT), Fast Neutron Spectroscopy, and Reactor Core Diagnostics.

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

View Original Abstract

\nDetectors based on synthetic chemical vapor deposition diamond gain importance in various neutron applications. The superior thermal robustness and the excellent radiation hardness of diamond as well as its excellent electronic properties make this material uniquely suited for rough environments, such as nuclear fission and fusion reactors. The intrinsic electronic properties of single-crystal diamond sensors allow distinguishing various interactions in the detector. This can be used to successfully suppress background of γ-rays and charged particles in different neutron experiments, such as neutron flux measurements in thermal nuclear reactors or cross-section measurements in fast neutron fields. A novel technique of distinguishing background reactions in neutron experiments with diamond detectors will be presented. A proof of principle will be given on the basis of experimental results in thermal and fast neutron fields.\n

Tech Support

Original Source

DOI: https://doi.org/10.1051/epjconf/201714603004