Response of a diamond detector sandwich to 14 MeV neutrons
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2016-02-08 |
| Journal | Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment |
| Authors | M. Osipenko, M. Ripani, G. Ricco, B. Caiffi, F. Pompili |
| Institutions | University of Rome Tor Vergata, Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata |
| Citations | 21 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Thin SCD Detectors for Fast Neutron Diagnostics
Section titled “Technical Documentation & Analysis: Thin SCD Detectors for Fast Neutron Diagnostics”Reference Paper: Osipenko et al., “Response of diamond detector sandwich to 14 MeV neutrons” (arXiv:1510.05415v3)
Executive Summary
Section titled “Executive Summary”This research validates the use of ultra-thin Single Crystal Diamond (SCD) detectors in a sandwich configuration for high-flux, high-energy neutron diagnostics, specifically addressing the extreme environmental demands of fusion reactors like ITER.
- Radiation Hardness: The use of 50 µm thick SCD crystals is projected to increase radiation hardness significantly, expected to withstand neutron fluences exceeding 1016 n/cm2, satisfying ITER Radial Neutron Camera (RNC) requirements.
- Detection Mechanism: The detector successfully measured 14 MeV neutrons via the 12C(n, α)9Be reaction, utilizing coincidence detection between two stacked SCD layers to suppress physical background noise.
- High Resolution: An intrinsic energy resolution of 240 keV FWHM was achieved, representing only 10% of the expected 14 MeV neutron energy spread (500 keV FWHM) at ITER.
- Complex Structure: The detector design required precise multi-layer fabrication, including HPHT substrates, p-type Boron-Doped Diamond (BDD) ohmic contacts, intrinsic SCD layers, custom Cr/Au metalization, and a 6LiF converter layer.
- Performance Metric: The measured 14 MeV neutron detection sensitivity was 5 x 10-7 counts cm2/n for the 3 x 3 mm2 active area.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the detector design and performance measurements:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Neutron Energy Measured | 14 | MeV | DT Fusion Source |
| Target Fluence (50 µm SCD) | > 1016 | n/cm2 | Expected radiation hardness limit |
| SCD Intrinsic Layer Thickness (Range) | 49 - 54 | µm | Active volume of the two SCDs |
| P-doped Layer Thickness (Range) | 15 - 26 | µm | Boron-doped ohmic contact layer |
| Metallic Contact Material | Cr / Au | nm | Cr (40 nm) as sticking layer; Au (80 nm) strips |
| LiF Converter Layer Thickness | 50 | nm | Used for thermal neutron calibration |
| Detector Active Area | 3 x 3 | mm2 | Size of the metallic contact |
| Bias Voltage Applied | -80 | V | Operational voltage |
| Electric Field Strength | 1.6 | V/µm | Calculated field across the intrinsic layer |
| Intrinsic Energy Resolution (FWHM) | 240 | keV | Resolution attributed to detector design |
| Total Measured Resolution (FWHM) | 870 | keV | Limited primarily by environmental EM noise |
| Detection Sensitivity (14 MeV) | 5 x 10-7 | counts cm2/n | Measured for the 3 x 3 mm2 detector |
| Coincidence Trigger Window | 64 | ns | Hardware trigger interval |
Key Methodologies
Section titled “Key Methodologies”The experiment relied on precise material engineering and a specialized coincidence detection setup to isolate the 12C(n, α)9Be reaction signal from background noise.
- Material Selection and Thinning: Electronic grade Single Crystal Diamond (SCD) was grown via MPCVD. The crystals were thinned to approximately 50 µm to maximize radiation hardness against fast neutrons, a critical requirement for long-term fusion reactor operation.
- Multi-Layer Fabrication: Each SCD detector was constructed with five distinct layers: HPHT substrate, a p-type Boron-Doped Diamond (BDD) ohmic contact layer, the intrinsic SCD active layer, a metallic anode, and a LiF converter layer.
- Custom Metalization: The metallic anode was applied by evaporating a 40 nm Chromium (Cr) layer, followed by 80 nm Gold (Au) strips (0.4 mm x 3 mm) used for grounding and electrical connection.
- Sandwich Configuration: Two SCD detectors were stacked with their metallic contacts facing each other to form a “sandwich” structure, enabling coincidence measurements of charged particles (α particles) produced by neutron interactions in the first crystal.
- Neutron Source and Calibration: 14 MeV neutrons were generated using a DT fusion generator (FNG). Energy calibration was performed using the highly exothermic 6Li(n, t)α reaction in the interposed 50 nm LiF layer.
- High-Speed Data Acquisition (DAQ): Signals were processed using custom fast charge amplifiers and a 10-bit digitizer operating at 5 Gs/s. Coincidence events were filtered offline by requiring a maximum 6 ns time difference between the two detector signals to reject EM noise and accidental background.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The successful replication and extension of this high-performance, radiation-hard detector requires specialized MPCVD diamond materials and advanced fabrication capabilities. 6CCVD is uniquely positioned to supply the necessary components for fusion diagnostics and high-energy physics research.
| Research Requirement | 6CCVD Solution & Capability | Technical Advantage for Replication/Extension |
|---|---|---|
| Ultra-Thin SCD Layers (50 µm) | Custom Thickness SCD: We provide electronic-grade Single Crystal Diamond (SCD) wafers with precise thickness control from 0.1 µm up to 500 µm. | Enables the production of thin detectors necessary to achieve the required radiation hardness (> 1016 n/cm2) for long-duration fusion experiments. |
| P-type Ohmic Contact Layer | Boron-Doped Diamond (BDD): 6CCVD offers custom-doped BDD layers (p-type) for stable ohmic contacts, replicating the 15 µm to 26 µm layers used in the study. | Ensures reliable charge collection and low leakage current, critical for high-temperature operation (up to 100 °C in ITER). |
| Custom Metalization (Cr/Au/LiF) | Advanced Metalization Services: We offer in-house deposition of Cr, Au, Ti, Pt, Pd, W, and Cu. We can precisely replicate the 40 nm Cr / 80 nm Au electrode structure and assist in integrating converter layers like LiF. | Guarantees high-quality, low-loss electrical contacts and facilitates complex multi-layer detector assembly (e.g., sandwich structures). |
| High Surface Quality | Precision Polishing (Ra < 1 nm): Our SCD wafers are polished to an atomic scale finish (Ra < 1 nm). | Minimizes surface defects that can contribute to leakage current and ensures optimal interface quality for subsequent metalization and layer deposition. |
| Custom Dimensions & Arrays | Large Format & Dicing: While the paper used 3 x 3 mm2 active areas, 6CCVD supplies plates/wafers up to 125 mm (PCD) and provides precision laser cutting and dicing services. | Supports scaling up the detector design into large-area arrays (e.g., 4x4 matrices) required for full-scale RNC systems. |
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in optimizing diamond material properties (thickness, doping, surface termination) for extreme environments. We can assist researchers and engineers in selecting the optimal Electronic Grade SCD or BDD material to meet the specific flux, temperature, and resolution requirements for similar Fast Neutron Diagnostics projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.