arXiv subjects

Arun Persaud

Publications and source records attributed to Arun Persaud.

At least 19 recordsLinked to original sources

arXiv2026

Characterization of GaN:Si and ZnO:Ga for position-resolved fast timing applications

We present the characterization of two fast, crystalline inorganic scintillators, silicon-doped gallium nitride (GaN:Si) and gallium-doped zinc oxide (ZnO:Ga), and compare their performance with cerium-doped yttrium aluminium perovskite (YAP:Ce) for in-vacuum alpha-detection applications that require high-performance timing, position, and energy resolution, such as 3D elemental mapping, medical imaging, and homeland security applications. In this paper, we propose ZnO:Ga and GaN:Si as high-performance drop-in replacements for the alpha detector in Associated Particle Imaging (API) systems. However, the results reported here also have wide applicability. Prior work has reported on polycrystalline forms of ZnO:Ga, which suffer from self-absorption. To our knowledge, GaN:Si has not been proposed to be used in API systems. We present room-temperature scintillation time constants obtained via X-ray-induced time-correlated single-photon counting for both proposed materials. They both exhibit exceedingly fast rise times of <15ps, and high brightness >1000ph/MeV with resolved alpha-peaks. Single-crystal ZnO:Ga and single-crystal GaN:Si yield single-component decays of 805ps and 32ps, respectively. Using a plastic scintillator reference setup, coincidence timing resolution (CTR) and detector timing resolution (DTR) measurements demonstrate a >3x improvement in timing resolution compared to traditional YAP:Ce. GaN:Si and ZnO:Ga exhibit (35(9))ps and (49(5))ps DTR, respectively, compared to(144(2))ps for conventional, single-crystal YAP:Ce. Finally, we evaluate their position resolution in an experimental setup designed for API and measure better than 0.2mm for YAP:Ce and approximately 1mm for GaN:Si. We obtain a position resolution of 0.3mm for ZnO:Ga from simulations. We also present alpha-induced ionoluminescence emission spectra that reveal direct, red-shifted near-bandgap emission.

physics.ins-det↗

arXiv2026

Precision cross section measurements of neutron-induced non-elastic gamma production reactions at 14 MeV

We present a technique for high-precision absolute measurements of gamma-ray production cross sections (n,xg) induced by 14 MeV neutrons. The technique is based on the Associated Particle Imaging (API) method, which tags individual neutrons emitted from a deuterium-tritium source with their associated alpha-particles, enabling coincidence-based suppression of lower-energy neutrons and room background signals, while also providing neutron flux measurements with uncertainties on the order of 1%. This compact, laboratory-scale technique has the potential to address gaps and discrepancies in existing cross section libraries at a fraction of the cost of large-scale dedicated facilities, with direct applications in active neutron interrogation, detector calibration, nuclear fusion science, and Monte Carlo simulations, among others. We demonstrate the technique through proof-of-concept experiments on thin and thick samples of natural Fe (1 mm, 8 mm) and natural C (2 mm, 10 mm). For Fe, gamma-ray production cross sections were measured for the 846.78 and 1238.33 keV transitions from the first and second excited states of 56Fe. For C, the (n,n'g) cross section was measured for the 4438.91 keV transition from the first excited state of 12C. Measurements were performed at 110 and 48 degrees relative to the neutron beam to characterize gamma-ray anisotropy. For the thin samples, the measured cross sections are 723 +/- 70 mb (56Fe, 846.78 keV, 110 deg), 303 +/- 42 mb (56Fe, 1238.33 keV, 110 deg), 755 +/- 106 mb (56Fe, 846.78 keV, 48 deg), 321 +/- 149 mb (56Fe, 1238.33 keV, 48 deg), 141 +/- 16 mb (12C, 4438.91 keV, 110 deg), and 279 +/- 105 mb (12C, 4438.91 keV, 48 deg). Uncertainties are dominated by counting statistics and detector efficiency calibration, both of which can be reduced in future experiments to achieve overall uncertainties of 5% or better.

nucl-ex↗

arXiv2026

Predicting Neutron Attenuation from Bulk Density and Moisture for Soil Carbon Measurement

Inelastic neutron scattering (INS) enables rapid, non-destructive in situ measurements of soil elemental composition over large soil volumes. Standard INS yields bulk elemental concentrations, but spatially resolved measurements require techniques such as Associated Particle Imaging (API), which pairs neutron detection with coincident alpha detection to reconstruct the location of the neutron interaction. One of the unique advantages of API is its capability to measure all major soil components simultaneously, allowing for the estimation of both bulk density and water content directly from the measured neutron-induced gamma-ray spectra. Accurate interpretation of bulk INS-API data depends on correcting for both gamma-ray and neutron attenuation in soil. Although gamma attenuation can be calculated from known mass attenuation coefficient data and density, neutron attenuation is more complex, depending on neutron energy, soil composition, bulk density, and hydrogen content from water and organic matter. We use Monte Carlo simulations of soils with varied compositions, bulk densities, and water contents to model neutron attenuation and develop a simple predictive model requiring only dry bulk density and volumetric water content. We validate this model experimentally using an INS-API system with controlled soil columns, finding agreement within 10 percent at 30 cm depth. This approach enables practical, field-ready correction of INS-API measurements for neutron attenuation, laying the groundwork for a self-consistent measurement framework that can address the elemental composition of soil carbon assessments.

physics.geo-ph↗

arXiv2025

Enhanced nuclear fusion in the sub-keV energy regime

Nuclear fusion requires overcoming or traversing a repulsive Coulomb barrier of hundreds of kiloelectronvolts, rendering the probability of fusion at sub-keV energies vanishingly small. Yet in condensed matter, the electronic and structural environment of reacting nuclei can profoundly alter fusion rates. Here we demonstrate that deuterium-deuterium fusion within metallic foils exhibits a pronounced enhancement and reaction yield plateau below energies of 2.5 keV- contrary to the expected exponential suppression with decreasing energy. Using a dual-chamber platform that combines electrochemical deuterium loading with ion-beam bombardment, we show that fusion yields in palladium and titanium hydrides are enhanced by over 10^18 compared to theoretical bare-nucleus fusion rates. These results demonstrate that access to low-energy fusion processes can be governed by materials degrees of freedom. This materials-driven fusion regime establishes a reproducible, tunable framework for studying and ultimately engineering nuclear reactions in solids. While the reaction rates reported here are low, these insights into materials-modulated fusion processes offer a potential foundation for understanding how condensed-matter environments could influence future fusion-energy concepts.

nucl-ex↗

arXiv2024

Optical and spin properties of nitrogen vacancy centers formed along the tracks of high energy heavy ions

Exposure of matter to high energy, heavy ions induces defects along the trajectories of the ions through electronic and nuclear energy loss processes. Defects, including color centers, can recombine or form along latent damage tracks in many materials, such as insulators and semiconductors. Latent tracks in diamond were only recently observed. Here, we report on color center formation in diamond along the latent tracks of 1 GeV gold and uranium ions. Using depth-resolved photoluminescence, we observe direct formation of single vacancy related color centers (GR1-centers) along the ion tracks. Mobile vacancies can form NV-centers with native nitrogen atoms during thermal annealing. Molecular dynamics simulations show that isolated vacancies and vacancy clusters form through electronic stopping processes, leading to color center formation along ion trajectories from the sample surface to a depth of about 25 microns. We further report on the creation of individually isolated quasi-1D chains of NV-centers by using 1 GeV Au ions with a dilute fluence. The individual 1D NV-chains appear as isolated bright luminescence strings and present competitive electron spin properties compared to a background of NV-centers. Such spin textures can be explored as building blocks for applications in quantum information processing and quantum sensing.

quant-ph↗

arXiv2023

Quantum emitter formation dynamics and probing of radiation induced atomic disorder in silicon

Near infrared color centers in silicon are emerging candidates for on-chip integrated quantum emitters, optical access quantum memories and sensing. We access ensemble G color center formation dynamics and radiation-induced atomic disorder in silicon for a series of MeV proton flux conditions. Photoluminescence results reveal that the G-centers are formed more efficiently by pulsed proton irradiation than continuous wave proton irradiation. The enhanced transient excitations and dynamic annealing within nanoseconds allows optimizing the ratio of G-center formation to nonradiative defect accumulation. The G-centers preserve narrow linewidths of about 0.1 nm when they are generated by moderate pulsed proton fluences, while the linewidth broadens significantly as the pulsed proton fluence increases. This implies vacancy/interstitial clustering by overlapping collision cascades. Tracking G-center properties for a series of irradiation conditions enables sensitive probing of atomic disorder, serving as a complimentary analytical method for sensing damage accumulation. Aided by ${\it ab}$ ${\it initio}$ electronic structure calculations, we provide insight into the atomic disorder-induced inhomogeneous broadening by introducing vacancies and silicon interstitials in the vicinity of a G-center. A vacancy leads to a tensile strain and can result in either a redshift or blueshift of the G-center emission, depending on its position relative to the G-center. Meanwhile, Si interstitials lead to compressive strain, which results in a monotonic redshift. High flux and tunable ion pulses enable the exploration of fundamental dynamics of radiation-induced defects as well as methods for defect engineering and qubit synthesis for quantum information processing.

quant-ph↗

arXiv2022

Effect of Localization on Photoluminescence and Zero-Field Splitting of Silicon Color Centers

The study of defect centers in silicon has been recently reinvigorated by their potential applications in optical quantum information processing. A number of silicon defect centers emit single photons in the telecommunication $O$-band, making them promising building blocks for quantum networks between computing nodes. The two-carbon G-center, self-interstitial W-center, and spin-$1/2$ T-center are the most intensively studied silicon defect centers, yet despite this, there is no consensus on the precise configurations of defect atoms in these centers, and their electronic structures remain ambiguous. Here we employ \textit{ab initio} density functional theory to characterize these defect centers, providing insight into the relaxed structures, bandstructures, and photoluminescence spectra, which are compared to experimental results. Motivation is provided for how these properties are intimately related to the localization of electronic states in the defect centers. In particular, we present the calculation of the zero-field splitting for the excited triplet state of the G-center defect as the structure is transformed from the A-configuration to the B-configuration, showing a sudden increase in the magnitude of the $D_{zz}$ component of the zero-field splitting tensor. By performing projections onto the local orbital states of the defect, we analyze this transition in terms of the symmetry and bonding character of the G-center defect which sheds light on its potential application as a spin-photon interface.

cond-mat.mtrl-sci↗

arXiv2022

Center-of-Mass Corrections in Associated Particle Imaging

Associated Particle Imaging (API) utilizes the inelastic scattering of neutrons produced in deuterium-tritium fusion reactions to obtain 3-D isotopic distributions within an object. The locations of the inelastic scattering centers are calculated by measuring the arrival time and position of the associated alpha particle produced in the fusion reactions, and the arrival time of the prompt gamma created in the neutron scattering event. While the neutron and its associated particle move in opposite directions in the center-of-mass (COM) system, in the laboratory system the angle is slightly less than 180 degree, and the COM movement must be taken into account in the reconstruction of the scattering location. Furthermore, the fusion reactions are produced by ions of different momenta, and thus the COM velocity varies, resulting in an uncertainty in the reconstructed positions. In this article, we analyze the COM corrections to this reconstruction by simulating the energy loss of beam ions in the target material and identifying sources of uncertainty in these corrections. We show that an average COM velocity calculated using the ion beam direction and energy can be used in the reconstruction and discuss errors as a function of ion beam energy, composition, and alpha detection location. When accounting for the COM effect, the mean of the reconstructed locations can be considered a correctable systematic error leading to a shift/tilt in the reconstruction. However, the distribution of reconstructed locations also have a spread that will introduce an error in the reconstruction that cannot be corrected. In this article, we will use the known stopping powers of ions in materials and reaction cross sections to examine the reconstruction uncertainties. We also discuss the impact of this effect on our API system.

physics.ins-det↗

arXiv2022

Defect engineering of silicon with ion pulses from laser acceleration

Defect engineering is foundational to classical electronic device development and for emerging quantum devices. Here, we report on defect engineering of silicon single crystals with ion pulses from a laser accelerator with ion flux levels up to 10^22 ions/cm^2/s. Low energy ions from plasma expansion of the laser-foil target are implanted near the surface and then diffuse into silicon samples that were locally pre-heated by high energy ions. We observe low energy ion fluences of ~10^16 cm^-2, about four orders of magnitude higher than the fluence of high energy (MeV) ions. In the areas of highest energy deposition, silicon crystals exfoliate from single ion pulses. Color centers, predominantly W and G-centers, form directly in response to ion pulses without a subsequent annealing step. We find that the linewidth of G-centers increase in areas with high ion flux much more than the linewidth of W-centers, consistent with density functional theory calculations of their electronic structure. Laser ion acceleration generates aligned pulses of high and low energy ions that expand the parameter range for defect engineering and doping of semiconductors with tunable balances of ion flux, damage rates and local heating.

cond-mat.mtrl-sci↗

arXiv2022

Collective Effects and Intense Beam-Plasma Interactions in Ion-Beam-Driven High Energy Density Matter and Inertial Fusion Energy

For the successful generation of ion-beam-driven high energy density matter and heavy ion fusion energy, intense ion beams must be transported and focused onto a target with small spot size. One of the successful approaches to achieve this goal is to accelerate and transport intense ion charge bunches in an accelerator and then focus the charge bunches ballistically in a section of the accelerator that contains a neutralizing background plasma. This requires the ability to control space-charge effects during un-neutralized (non-neutral) beam transport in the accelerator and transport sections, and the ability to effectively neutralize the space charge and current by propagating the beam through background plasma. As the beam intensity and energy are increased in future heavy ion fusion (HIF) drivers and Fast Ignition (FI) approaches, it is expected that nonlinear processes and collective effects will become much more pronounced than in previous experiments. Making use of 3D electromagnetic particle-in-cell simulation (PIC) codes (BEST, WARP-X, and LTP-PIC, etc.), the theory and modelling studies will be validated by comparing with experimental data on the 100kV Princeton Advanced Test Stand, and future experiments at the FAIR facility. The theoretical predictions that are developed will be scaled to the beam and plasma parameters relevant to heavy ion fusion drivers and Fast Ignition scenarios. Therefore, the theoretical results will also contribute significantly toward the long-term goal of fusion energy production by ion-beam-driven inertial confinement fusion.

physics.plasm-ph↗

arXiv2022

Single Phonon Detection for Dark Matter via Quantum Evaporation and Sensing of $^3$Helium

Dark matter is five times more abundant than ordinary visible matter in our Universe. While laboratory searches hunting for dark matter have traditionally focused on the electroweak scale, theories of low mass hidden sectors motivate new detection techniques. Extending these searches to lower mass ranges, well below 1 GeV/c$^2$, poses new challenges as rare interactions with standard model matter transfer progressively less energy to electrons and nuclei in detectors. Here, we propose an approach based on phonon-assisted quantum evaporation combined with quantum sensors for detection of desorption events via tracking of spin coherence. The intent of our proposed dark matter sensors is to extend the parameter space to energy transfers in rare interactions to as low as a few meV for detection of dark matter particles in the keV/c$^2$ mass range.

hep-ex↗

arXiv2021

An all-digital associated particle imaging system for the 3D determination of isotopic distributions

Associated particle imaging (API) is a non-destructive nuclear technique for the 3D determination of isotopic distributions. By detecting the alpha particle associated with the emitted neutron in the deuterium-tritium fusion reaction with a position- and time-resolving detector, the direction of the 14.1 MeV neutron and its time of emission can be determined. Employing this method, isotope characteristic gamma rays emitted in inelastic neutron scattering events can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector was designed, constructed, and characterized. The system was tested with common soil elements and shown to be sensitive to 12C, 16O, 28Si, 27Al, and 56Fe. New aspects of our approach are the use of a yttrium-aluminum-perovskite (YAP) scintillator, using a sapphire window instead of a fiber-optic faceplate for light transport to the photomultiplier, and the all-digital data acquisition system. We present a description of the system with simulations and experimental results that show a position resolution on the alpha detector of 1 mm, a depth resolution using a LaBr3 detector of 6.2 cm, and an angular resolution of 4.5 degrees. Additionally, we present single-element gamma response measurements for the elements mentioned above together with a comparison to Monte Carlo simulations (MCNP6).

physics.ins-det↗

arXiv2021

Fast Grain Mapping with Sub-Nanometer Resolution Using 4D-STEM with Grain Classification by Principal Component Analysis and Non-Negative Matrix Factorization

High-throughput grain mapping with sub-nanometer spatial resolution is demonstrated using scanning nanobeam electron diffraction (also known as 4D scanning transmission electron microscopy, or 4D-STEM) combined with high-speed direct electron detection. An electron probe size down to 0.5 nm in diameter is implemented and the sample investigated is a gold-palladium nanoparticle catalyst. Computational analysis of the 4D-STEM data sets is performed using a disk registration algorithm to identify the diffraction peaks followed by feature learning to map the individual grains. Two unsupervised feature learning techniques are compared: Principal component analysis (PCA) and non-negative matrix factorization (NNMF). The characteristics of the PCA versus NNMF output are compared and the potential of the 4D-STEM approach for statistical analysis of grain orientations at high spatial resolution is discussed.

physics.app-ph↗

arXiv2021

Direct formation of nitrogen-vacancy centers in nitrogen doped diamond along the trajectories of swift heavy ions

We report depth-resolved photoluminescence measurements of nitrogen-vacancy (NV$^-$) centers formed along the tracks of swift heavy ions (SHIs) in type Ib synthetic single crystal diamonds that had been doped with 100 ppm nitrogen during crystal growth. Analysis of the spectra shows that NV$^-$ centers are formed preferentially within regions where electronic stopping processes dominate and not at the end of the ion range where elastic collisions lead to formation of vacancies and defects. Thermal annealing further increases NV yields after irradiation with SHIs preferentially in regions with high vacancy densities. NV centers formed along the tracks of single swift heavy ions can be isolated with lift-out techniques for explorations of color center qubits in quasi-1D registers with an average qubit spacing of a few nanometers and of order 100 color centers per micrometer along 10 to 30 micrometer long percolation chains.

cond-mat.mtrl-sci↗

arXiv2019

An Associated Particle Imaging System for Soil-Carbon Measurements

We present first results from experimental data showing the capabilities of an Associated Particle Imaging system to measure carbon in soil and other elements. Specifically, we present results from a pre-mixed soil sample containing pure sand (SiO$_2$) and 4% carbon by weight. Because the main isotopes of all those three elements emit characteristic high-energy gamma rays following inelastic neutron scattering, it is possible to measure their distribution with our instrument. A 3D resolution of several centimeters in all dimensions has been demonstrated.

physics.ins-det↗

arXiv2018

Position Sensitive Alpha Detector for an Associate Particle Imaging System

Associated Particle Imaging (API) is a nuclear technique that allows for the nondestructive determination of 3D isotopic distributions. The technique is based on the detection of the alpha particles associated with the neutron emitted in the deuterium-tritium (DT) fusion reaction, which provides information regarding the direction and time of the emitted 14 MeV neutron. Inelastic neutron scattering leads to characteristic gamma-ray emission from certain isotopes, for example C-12, that can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector is under development for the nondestructive quantification of carbon distribution in soils. This paper describes the design of the alpha detector, detector response simulations, and first experimental results. The alpha detector consists of a Yttrium Aluminum Perovskite (YAP) scintillator mounted on the inside of a neutron generator tube. The scintillation light propagates through a sapphire window to a position-sensitive photomultiplier tube mounted on the outside. The 16x16 output signals are connected through a resistive network for a 4-corner readout. The four readout channels are amplified, filtered, and then digitized for the calculation of the alpha position. First test results demonstrate that an excellent alpha position resolution, better than the 1 mm FWHM required by the application, can be achieved with this detector design.

physics.ins-det↗

arXiv2018

Multi-beam RF accelerators for ion implantation

We report on the development of a radio frequency (RF) linear accelerator (linac) for multiple-ion beams that is made from stacks of low cost wafers. The accelerator lattice is comprised of RF-acceleration gaps and electrostatic quadrupole focusing elements that are fabricated on 10-cm wafers made from printed circuit board or silicon. We demonstrate ion acceleration with an effective gradient of about 0.5 MV per meter with an array of 3 by 3 beams. The total ion beam energies achieved to date are in the 10 keV range with total ion currents in tests with noble gases of ~0.1mA. We discuss scaling of the ion energy (by adding acceleration modules) and ion currents (with more beams) for applications of this multi-beam RF linac technology to ion implantation and surface modification of materials.

physics.acc-ph↗

arXiv2017

Optimizing Beam Transport in Rapidly Compressing Beams on the Neutralized Drift Compression Experiment - II

The Neutralized Drift Compression Experiment-II (NDCX-II) is an induction linac that generates intense pulses of 1.2 MeV helium ions for heating matter to extreme conditions. Here, we present recent results on optimizing beam transport. The NDCX-II beamline includes a 1-meter-long drift section downstream of the last transport solenoid, which is filled with charge-neutralizing plasma that enables rapid longitudinal compression of an intense ion beam against space-charge forces. The transport section on NDCX-II consists of 28 solenoids. Finding optimal field settings for a group of solenoids requires knowledge of the envelope parameters of the beam. Imaging the beam on scintillator gives the radius of the beam, but the envelope angle dr/dz is not measured directly. We demonstrate how the parameters of the beam envelope (r, dr/dz, and emittance) can be reconstructed from a series of images taken at varying B-field strengths of a solenoid upstream of the scintillator. We use this technique to evaluate emittance at several points in the NDCX-II beamline and for optimizing the trajectory of the beam at the entry of the plasma-filled drift section.

physics.acc-ph↗