A Novel Fast Readout, Gamma Detector System for Nuclear Fingerprinting

At a Glance

Metadata	Details
Publication Date	2017-01-01
Journal	CERES (Cranfield University)
Authors	A. Giroletti, J. J. Velthuis, Thomas R. Scott
Analysis	Full AI Review Included

Technical Documentation & Analysis: Fast Readout Gamma Detector Systems

This document analyzes the research paper “A novel, fast readout, gamma detector system for nuclear fingerprinting” to highlight the critical role of Chemical Vapor Deposition (CVD) Diamond and to position 6CCVD’s advanced material capabilities as the ideal solution for replicating and advancing this high-radiation detection technology.

Executive Summary

The research validates a multi-detector matrix concept designed for rapid, high-dose gamma spectroscopy, essential for nuclear decommissioning and post-incident cleanup.

Core Challenge Addressed: Overcoming the limitations of traditional high-precision gamma spectroscopy (long shaping times, low maximum count rate) in extreme radiation environments.
Novel Solution: A multi-material detector matrix (Si, GaAs, UO₂, CZT, and Diamond) utilizing fast amplification and thresholding techniques to simultaneously count events above specific energy bins.
Diamond’s Critical Role: CVD Diamond is selected as a primary detector material due to its superior radiation hardness, chemical inertness, high band gap (5.5 eV), and extremely low leakage current (pA), ensuring reliable operation where other semiconductors would saturate.
Validation: Monte Carlo simulations (Geant4) successfully demonstrated the system’s ability to identify and quantify common radionuclides (e.g., ²⁴¹Am, ¹³⁷Cs, ⁶⁰Co) by analyzing electron-hole pair production thresholds.
Deployment Advantage: The compact, lightweight design is suitable for deployment on Unmanned Aerial Vehicles (UAVs) and Remotely Operated Vehicles (ROVs), minimizing human radiation exposure.
6CCVD Value Proposition: 6CCVD provides the necessary high-quality, low-impurity Single Crystal Diamond (SCD) wafers, custom dimensions, and metalization services required for fabricating these next-generation radiation-hard detectors.

Technical Specifications

The following table extracts key material properties and operational parameters relevant to the detector design, focusing on Diamond and comparative semiconductors (Table 1, Page 2, and Page 4).

Parameter	Diamond Value	Unit	Context
Density	3.52	g/cm³	High density aids stopping power
Band Gap	5.5	eV	High intrinsic resistivity
Energy per E-H Pair (ε)	13	eV	Low energy required for charge generation
Electron Mobility (μ_e)	2000	cm²V^-1s^-1	High charge transport speed
Hole Mobility (μ_h)	1600	cm²V^-1s^-1	High charge transport speed
Bias Voltage Range	100 - 500	V	Operating range
Leakage Current	pA	Extremely low, crucial for high sensitivity
Optimal Detector Thickness (SCD)	500	µm	Optimized thickness for multi-detector system
Sensor Size (Simulation)	5 x 5	mm	Fixed size used in Geant4 simulations
Readout Discrimination Factors	Up to 52	N/A	Used across several detector materials

Key Methodologies

The experimental validation relied on advanced simulation and a specialized fast readout chain designed to bypass the limitations of traditional spectroscopic measurements.

Simulation Environment: All studies were performed using the Geant4 Monte Carlo simulation toolkit, modeling the source 2 m away from the detector matrix, separated by air and an 8 µm Kapton window.
Detector Matrix Design: A composite system utilizing five distinct semiconductor materials (Si, GaAs, UO₂, CZT, and Diamond) to exploit differences in gamma ray interaction cross sections (Photoelectric Effect, Compton Scattering, Pair Production).
Thickness Optimization: Detector thickness was varied (50 µm to 2 mm) to optimize gamma ray attenuation and stopping power. The optimal thickness for Diamond was determined to be 500 µm.
Fast Readout Technique: The system circumvents slow shaping times by employing fast amplifiers and thresholding. This method counts the number of events in each detector material that exceed specific electron-hole pair production thresholds.
Electronics Chain: The readout chain consists of a fast, low-noise, charge-sensitive preamplifier (Amptek A250), a high-speed op-amp (ADA4860), and a Field-Programmable Gate Array (FPGA) utilizing the MAROC3 chip to record total counts across up to 52 threshold bins.
Energy Reconstruction: Radionuclide identification is achieved by correlating the number of electron-hole pairs produced above the threshold with known energy levels of concern (Table 2, Page 3).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-performance CVD diamond materials and custom engineering services necessary to transition this fast-readout gamma detector concept from simulation to hardware realization.

Applicable Materials

To replicate or extend this research, the highest quality, low-impurity diamond is required to maximize charge collection efficiency and minimize leakage current, especially under high bias voltage (up to 500 V).

Application Requirement	6CCVD Material Solution	Key Benefit
High Radiation Tolerance	Single Crystal Diamond (SCD)	Detector Grade, high purity, low nitrogen content, ensuring maximum charge carrier lifetime and radiation hardness.
Large Area Coverage	Polycrystalline Diamond (PCD)	Available in plates/wafers up to 125mm for large-area detector arrays or tiling applications.
Custom Electrode Integration	Metalized SCD/PCD	Internal capability for depositing Au, Pt, Ti, or W electrodes, crucial for applying the required 100-500 V bias voltage.

Customization Potential

The simulation determined an optimal Diamond thickness of 500 µm and used a 5 x 5 mm sensor size. 6CCVD’s capabilities align perfectly with these requirements and offer scalability for production:

Custom Dimensions: 6CCVD provides SCD wafers in the required 500 µm thickness (within the 0.1 µm - 500 µm SCD range) and can laser-cut or dice the material to precise 5 x 5 mm dimensions, or larger custom sizes for advanced detector matrices.
Surface Finish: Achieving optimal charge collection requires a pristine surface. 6CCVD guarantees Ra < 1nm polishing for SCD, minimizing surface defects that could trap charge carriers or increase leakage current.
Metalization Services: The detector design requires robust, low-resistance electrodes. We offer custom, multi-layer metalization stacks (e.g., Ti/Pt/Au) tailored for high-voltage bias and integration with the fast readout electronics (Amptek A250/MAROC3).

Engineering Support

The successful implementation of this multi-detector system relies on precise material selection and optimization of the detector geometry (thickness, electrode placement).

Material Selection for Extreme Environments: 6CCVD’s in-house PhD team specializes in optimizing CVD diamond properties (e.g., nitrogen concentration, defect density) specifically for high-dose gamma spectroscopy projects. We assist engineers in selecting the ideal SCD grade to maximize signal-to-noise ratio and operational lifetime in extreme environments.
Global Supply Chain: We offer reliable Global Shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond wafers to research facilities and manufacturing partners worldwide.

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

View Original Abstract

Technical paper presented at the 2017 Defence and Security Doctoral Symposium. In order to be effective, decommissioning of nuclear facilities as well as recovery procedures following a nuclear accident require a precise estimation of the amount, type, and topological distribution of nuclear material present at the scene. In this work we present a novel, fast readout, spectroscopy system suitable for high radiation level environment which we estimate to be 10 times faster than current deployed systems. The proposed device is based on semiconductor materials: when hit by a photon they generate electron-hole pairs, which in turn give rise to a current pulse that is proportional to the incident photon energy. This mechanism allows recognizing the incident radiation source. The proposed apparatus is composed of five semiconductor materials (Silicon, Gallium Arsenide, Uranium Dioxide, Cadmium Zinc Telluride and Diamond), which allow the cover the detection of a wide range of energies. This multi-material platform enables the precise identification of 27 isotopes which can be found after a nuclear accident or when a nuclear plant is in decommissioning. The amplifier stage uses the Amptek A250 charge sensitive preamplifier which shows low-noise (<100 electrons rms) and fast (rise time 2.5 ns) response behaviours. The readout chain consists of a MAROC3 chip and an FPGA (field programmable gate array). To prove the validity of the system, several Monte Carlo simulations, using Geant4, were performed. Simulation results have shown that gamma spectroscopy and material abundance study are possible. The system is under test at the present.

Tech Support

Original Source

DOI: https://doi.org/10.17862/cranfield.rd.5589823.v1