CHARACTERIZATION AND COMPARSION OF NEUTRON GENERATORS OF IEC AND LINEAR D-T BY THE SPECTROMETRIC SYSTEM NGA-01
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | EPJ Web of Conferences |
| Authors | ZdenÄk MatÄj, Michal KoĆĄĆ„ĂĄl, EvĆŸen NovĂĄk, P. Alexa, Radim UhlĂĄĆ |
| Institutions | University of Defence, Research Centre Rez |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis characterizes and compares the neutron fields generated by a Linear Deuterium-Tritium (D-T) generator and an Inertial Electrostatic Confinement (IEC) generator using advanced spectroscopy.
- Core Achievement: Successful characterization of two distinct D-T neutron fields using the NGA-01 spectrometric system (stilbene scintillator) and validation with a radiation-hard diamond detector and MCNP6 simulations.
- Linear Generator Kinematics: The Linear generator (MP320, VSB) confirmed the theoretical prediction that D-T neutron energy is highly dependent on the emission angle relative to the deuteron beam axis, spanning 13.3 MeV to 14.8 MeV.
- IEC Generator Complexity: The IEC generator (NSD-350, CVR) produced a complex spectrum, notably splitting the primary 14 MeV D-T peak into two distinct peaks when measured in the plane perpendicular to the generator axis.
- Dual-Peak Explanation: This dual-peak structure is attributed to the unique kinematics within the IEC accelerator tube, reflecting two major interaction cases: accelerated ions hitting stationary particles, and accelerated ions hitting particles with similar energy but opposite momentum.
- Spectrometry Capability: The NGA-01 system, utilizing an active MOS-FET voltage divider, achieved excellent linearity and high count rate capability (greater than 105 counts/s) for simultaneous neutron/gamma spectroscopy.
- Room Effect Quantification: Experimental results quantified the room effect (scattered neutrons) in the VSB lab, showing that background contribution is negligible at the D-T peak energy but plays a major role in the lower energy spectrum (below 4 MeV).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Linear Generator (MP320) | |||
| Operating Voltage | 80 | kV | Continuous regime |
| Operating Beam Current | 60 | ”A | Continuous regime |
| Total Neutron Yield | 108 | neutrons/s | Operating condition |
| DT Neutron Energy Range | 13.3 - 14.8 | MeV | Angular dependent emission |
| Initial Tritium Activity | 70 | GBq | MP320 specification |
| IEC Generator (NSD-350) | |||
| Operating Voltage | 80 | kV | Optimal for temperature stability |
| Operating Beam Current | 100 | mA | Optimal for temperature stability |
| Operating Neutron Emission | 5 x 109 | neutrons/s | At 8 kW power |
| Maximum Neutron Emission | 1010 | neutrons/s | At 160 kV, 150 mA (24 kW) |
| Reaction Chamber Volume | 5 | dm3 | Active volume |
| Tritium Activity (Getter) | 500 | GBq | NSD-350 specification |
| Spectrometry System (NGA-01) | |||
| Detector Type | Stilbene | N/A | Cylindrical 45x45 mm scintillator |
| Digitization Frequency | 500 | MHz | Sampling rate |
| Resolution | 12 | bits | Per input channel |
| Maximum Pulse Rate | > 105 | counts/s | Achieved via active voltage divider |
| Measured Neutron Range | 1 - 15 | MeV | Stilbene detector capability |
Key Methodologies
Section titled âKey MethodologiesâThe characterization involved a combination of experimental measurements and computational modeling to accurately determine the neutron flux and energy distribution for both generator types.
- Spectrometry System (NGA-01) Setup: The core measurement system used a stilbene scintillation detector coupled with a Hamamatsu photomultiplier and an active voltage divider (based on MOS-FET transistors) to ensure excellent linearity and high pulse rate capability.
- Data Acquisition and Digitization: Input signals were processed via a preamplifier and digitizing card. Digitization occurred at a sampling frequency of 500 MHz with 12-bit resolution. Advanced integration algorithms were applied directly in the FPGA.
- Spectral Calculation: Raw recoiled proton spectra (measured by the stilbene detector) were converted into neutron energy spectra using deconvolution techniques based on the Maximum Likelihood Estimation (MLE) method.
- Validation Measurement: Results were independently verified using a diamond detector, which confirmed the observed spectral shifts (Linear generator) and the dual-peak structure (IEC generator).
- Linear Generator Measurement: Neutron spectra were measured at various angles (0°, 45°, 90°, 135°, 180°) relative to the deuteron beam axis to confirm the angular dependence of the D-T neutron energy peak.
- IEC Generator Measurement: The IEC generator was operated vertically (80 kV, 100 mA). Measurements focused on positions perpendicular to the generator axis, where the unique dual-peak structure resulting from electrostatic confinement kinematics was most prominent.
- Computational Modeling: Theoretical models for both generators were constructed based on manufacturer documentation and simulated using the MCNP6 code to provide a baseline for comparison with experimental results.
Commercial Applications
Section titled âCommercial ApplicationsâThe technology describedâhigh-flux D-T neutron generation and high-rate, mixed-field spectroscopy using stilbene and diamond detectorsâis critical for several high-tech engineering and industrial sectors.
- Industrial Inspection and Defectoscopy: Neutron generators are used for non-destructive testing (NDT) of large or dense materials (e.g., aircraft components, concrete structures) where X-rays or gamma rays are ineffective.
- Oil and Gas Exploration: Neutron logging tools utilize D-T sources to determine porosity, fluid saturation, and lithology of subsurface formations.
- Nuclear Security and Active Interrogation: High-yield neutron sources are essential for active interrogation systems used in homeland security to detect shielded nuclear materials (e.g., cargo scanning).
- Fusion Energy Research: Characterization of 14 MeV neutron fields is fundamental for developing and testing materials and diagnostics for future D-T fusion reactors (e.g., ITER).
- Radiation Hard Spectroscopy: The use of diamond detectors, which are highly radiation-hard, is crucial for monitoring neutron and gamma fields in high-flux environments, such as near accelerators or within reactor cores.
- Radioisotope Production: Neutron generators can be used to produce short-lived radioisotopes for medical imaging (PET/SPECT) or industrial tracers via neutron activation.
View Original Abstract
This article focuses on description of two different neutron fields from linear and cylindrical Inertial Electrostatic Confinement (IEC) neutron generators. Both of these generators are well defined and commonly used. They use a deuterium-tritium reaction that produces neutrons with energies in the range 13 - 16 MeV, depending on the direction and the energy of the incoming deuterium nucleus. Two-parametric spectrometric system for neutron/gamma mixed fields NGA-01 was used to characterize neutron spectra in the proximity of generators. The cylindrical 45x45 mm stilbene scintillator was connected to this device using an active voltage divider. This way, we were able to measure neutron energies in the range 1 - 15 MeV while filtering out gamma radiation, even when counts per second is high. For the neutron spectrum calculation recoil spectra using deconvolution through maximum likelihood estimation was used. Measured neutron spectra have been compared with simulations realized via MCNP6. According to the theoretical prediction, these two types of generators produce different neutron fields. In case of the linear generator the target is very close to point located tritium bombarded by deuterons. Thus the neutron spectrum varies depending on the angle between the detector axis and the axis of the generator. Both experimental results and simulation show a shift of the neutron energy peak in pulse height histogram. For IEC type generators the neutron spectrum is more complicated. The shape and the position of the neutron energy peak depend heavily on the position of the detector. The most prominent effect is in the position in the plane perpendicular to the generator axis. In this case, the peak splits into two peaks that can be measured and distinguished. These results were verified by the diamond detector which was also used for characterization of the IEC type generator.