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Iliev, Metodi

Publications and source records attributed to Iliev, Metodi.

14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Solid, structured composite neutron detectors with high dynamic range capability

Neutron detectors are essential across disciplines such as fundamental science, nuclear security, safeguards, and civilian applications. While 3 He-filled gas proportional counters have long been revered for their efficacy in detecting thermal neutrons and praised for their efficiency, neutron/gamma discrimination, and stability, the scarcity of 3He has spurred a search for alternatives. Here, we explore a solid structured scintillating particle composite (SPC) consisting of 6 Li-containing scintillating glass particles within an acrylic matrix as a neutron detector for high dynamic range applications. We show for the first time that an SPC neutron detector can boast an intrinsic detection efficiency of 0.261% for pure 252 Cf fission neutrons and an overall neutron detection efficiency of (0.546 ± 0.003)% at the Neutron Free-in-Air facility while being able to function in an intense gamma-ray environment. We also show that the SPC neutron detector supports fast neutron capture times and enables a dual-readout scheme that extends the detector dynamic range to high incident neutron fluxes. A scalable fabrication process allows for tailoring the SPC detector properties to the requirements of specific applications. Good agreement is found between the experimental results taken with a National Institute of Standards and Technology traceable 252 Cf source and the coupled MCNP6 and optical-ray-tracing simulations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

High-yield and high-angular-fluence neutron generation from deuterons accelerated by laser-driven collisionless shock

Since a bright collimated neutron source is an essential tool for global security missions and fundamental scientific research. In this paper, we study a compact high-yield and high-angular-fluence neutron source particularly suitable for high-energy neutron applications utilizing the breakup reaction of laser-driven deuterons in a 9 Be converter. The neutron generation scaling from such a reaction is used to guide the choice and optimization of the acceleration process for bulk ions in a low density CD 2 foam. In particular, the collisionless shock acceleration mechanism is exploited with proper choice in the laser and target parameter space to accelerate these ions toward energies above the temperature of the distribution. Particle-in-cell and Monte Carlo simulations are coupled here to investigate this concept and possible adverse effects as well as the contribution from the surface ions accelerated and the optimal converter design. The simulation results indicated that our design can be a practical approach to increase both the neutron yield and angular fluence of laser-driven neutron sources, reaching >10 11 neutron/pulse (or >10 8 neutron/J) and >10 11 neutron/sr (or >10 8 neutron/sr/J) with present-day kJ-class high-power lasers. Such developments will advance fundamental neutron science, high precision radiography, and other global security applications with laser-driven sources.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Investigations of radiation damaged arranged scintillating particle composites

Composites consisting of periodically arranged scintillating particles within an acrylic (poly methyl methacrylate) matrix are excellent templates for the gamma-insensitive detection of fast neutrons. In order to study the impact of radiation damage on acrylic-based scintillating particle composites, we exposed acrylic samples to different doses of fast neutrons up to 119.7 kGy and investigated the change in optical characteristics using optical absorption spectroscopy in the 200–800 nm wavelength range. The experimental results are compared to coupled MCNP6 and optical ray-tracing (FRED) simulations, and qualitative agreement is found. Neutron-induced radiation damage in the acrylic matrix manifests as a red-shift in the ultra-violet absorption edge of the acrylic and a corresponding decrease in the light propagation efficiency, which leads to detector performance degradation. We show for the first time that the effects of radiation damage can be mitigated by the use of wavelength-shifting coatings. We predict that composites with wavelength-shifting coatings can enable neutron detectors with high tolerance against neutron-induced radiation damage, a property that is particularly desired for neutron detection in high radiation environments.

36 MATERIALS SCIENCE↗
DOE OSTI2021

PSMC Upgrade Development Documentation and Functional Testing

The functional verification consists of verifying that the calibration (a.k.a. gain matching) is accurate and that there is no double pulsing or signal cross talk and interference. The calibration is shown to be satisfactory from the plateau plots on the right. The absence of double pulsing and cross talk can be seen in the time-interval diagram below. Both phenomena are manifested by spikes in the time interval distribution around 1µs to 5µs. No such spike is present.

3-He detector electronics↗
DOE OSTI2019

Report on Task USA A 0931 (A.252) Implementation of Fast, Front-End Electronics for Improved Low-Dead Time Neutron Counting

The International Atomic Energy Agency's (IAEA) Department of Safeguards is working on the elaboration and implementation of advanced Non-Destructive Assay (NDA) methods, generally known as neutron noise analysis, for the verification of critical and sub-critical cores containing substantial quantities of direct use nuclear material. These verification methods rely on interpreting time properties of the neutron multiplication process, which are to be extracted from measured neutron pulse trains. The interpretations are highly dependent on the quality of the measured data, which is directly related to the capability of an employed neutron detector to resolve very close detection events originating from neutron bursts produced in a highly multiplying medium. Therefore, the application of detectors with minimum dead-time, pile-up, and other distortion effects is required. This report describes the work under Task USA A 0931 (A.252 Implementation of fast, front-end electronics for improved low-dead time neutron counting).

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Scintillation detectors

Devices/apparatuses are disclosed that include a photoemitting component, a photosensitive component deposited on the photoemitting component, a charge collection component, and a hollow enclosure for housing the photoemitting component, the photosensitive component, the charge collection component, or combinations thereof. Methods for making and using the apparatuses are also disclosed.

Ianakiev, Kiril D.↗
DOE OSTI2019

High count rate thermal neutron detectors and electronics

Improved, high count rate thermal neutron counters and electronics enabling new, higher measurement capabilities are disclosed. Next generation 3He and 10B tubes may include an electronics package capable of operating at higher count rates and in higher gamma fields and providing more efficient use of 3He gas. Conventional detector systems may also be upgraded, providing a possible solution to measure spent nuclear fuel with high neutron efficiency previously not possible in 235U fission counter systems. Switching the number of tubes per amplifier allows use of the measured nuclear material for a calibration standard for dead time correction, increasing accuracy of neutron measurements systems. An optimized detector geometry and advanced electronics with double pulse filtering and a dual channel readout may be provided. A bipolar shaper may improve dead time, provide efficient detector use, reduce double pulsing, facilitate high count rate measurements, and allow remote threshold setting.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Characterizing laser-plasma ion accelerators driving an intense neutron beam via nuclear signatures

Compact, bright neutron sources are opening up several emerging applications including detection of nuclear materials for national security applications. At Los Alamos National Laboratory, we have used a short-pulse laser to accelerate deuterons in the relativistic transparency regime. These deuterons impinge on a beryllium converter to generate neutrons. During the initial experiments where these neutrons were used for active interrogation of uranium and plutonium, we observed β-delayed neutron production from decay of 9 Li, formed by the high-energy deuteron bombardment of the beryllium converter. Analysis of the delayed neutrons provides novel evidence of the divergence of the highest energy portion of the deuterons (i.e., above 10 MeV/nucleon) from the laser axis, a documented feature of the breakout afterburner laser-plasma ion acceleration mechanism. Furthermore, these delayed neutrons form the basis of non-intrusive diagnostics for determining the features of deuteron acceleration as well as monitoring neutron production for the next generation of laser-driven neutron sources.

43 PARTICLE ACCELERATORS↗