Neutron Transmutation Doping Research Articles

First measurement of Gallium Arsenide as a low-temperature calorimeter

In the quest for direct dark matter detection, innovative approaches to lower the detection threshold and explore the sub-GeV mass range, have gained high relevance in the last decade. This study presents the pioneering use of Gallium Arsenide (GaAs) as a low-temperature calorimeter for probing dark matter-electron interactions within the DAREDEVIL (DARk-mattEr DEVIces for Low energy detection) project. Our experimental setup features a GaAs crystal at an ultralow temperature of 15 mK, coupled with a Neutron Transmutation Doped Germanium (NTD-Ge) thermal sensor for precise energy estimation. This configuration is the first step towards detecting single electrons scattered by dark matter particles within the GaAs crystal, to improve the sensitivity to low-mass dark matter candidates significantly. Taking advantage of the production of optical phonons in polar materials such as GaAs gives the possibility to study the scattering of sub-MeV dark matter. This paper presents a detailed analysis of the detector’s response, using a calibration spectrum using α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document} particles and X-ray events. While the results do not meet the ambitious eV scale threshold yet, they establish a solid benchmark for assessing the detector’s current performance and sensitivity. This work not only highlights the detector’s potential but also sets the stage for future enhancements aimed at achieving the eV threshold, underscoring the promising direction of this detector technology. These findings demonstrate the feasibility of using GaAs as a cryogenic calorimeter and hence open new avenues for investigating the elusive nature of dark matter through innovative direct detection techniques.

Electrodeposition of Thin Silicon Films for Neutron Transmutation Doping

Thin silicon films were electrodeposited on glassy carbon (GC) from the KF-KCl (2:1)—75 mol% KI—1.5 mol% K2SiF6 melt under potentiostatic condition at 973 K. The synthesized films were single-phase, continuous, dense, and free from unwanted impurities. Neutron transmutation doping (NTD) of the samples was performed in the IVV-2M research reactor (RR) at a thermal neutron flux density of 1.8 × 1013 cm−2s−1 for 7.7 h in order to form the 31P isotope dopant. The irradiated samples were studied by scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, mass spectrometry, and gamma-ray spectrometry. Some excess of the minimum significant specific activity of the irradiated samples was explained by the formation of the 182Ta isotope due to the presence of tantalum traces in the GC substrate. The formation of the 31P isotope by the NTD process was confirmed. The calculated values of 31P concentration and electrical resistivity were 4.9 × 1016 cm–3 and 0.15 Ω·cm, respectively.

Measuring the thermal neutron fluence of NTD-Ge using the self-monitoring method

Thermal neutron irradiation in reactors is widely used in the different frontier fields, including advanced materials and semiconductor devices. The total thermal neutron fluence is a key parameter in various applications. In this paper, we demonstrate a method to determine the total thermal neutron fluence during the manufacture of Neutron Transmutation Doping Germanium (NTD-Ge). The NTD-Ge samples are irradiated at the China Advanced Research Reactor, and their total neutron fluences are measured using the activity of radionuclide 71Ge through the reaction process 70Ge(n,γ)→71Ge ⟶EC71Ga. The activity of 71Ge in a NTD-Ge sample is obtained by measuring the event rates of the gallium KX-rays with energies of 9.2 and 10.3 keV using a Micro-Megas Detector (MMD) and a Silicon Drift Detector (SDD) individually, and incorporating with the correction of detection efficiencies estimated with the Monte Carlo simulation based on the GEANT4 toolkit. The measurements yield the total thermal neutron fluence with high precision, and the results are well consistent with each other between the MMD and SDD method.

Neutron-induced damage simulations using MCNP6 and SRIM codes: Beyond neutron transmutation doping of silicon

When a high degree of consistency and precision in dopant (phosphorous) distribution is required, the NTD technique is used, but neutron irradiation made damages in the silicon. This study focused on neutron-induced damage to silicon, as well as phosphorus produced inside the irradiated samples. The evolution of the resistivity and the surface morphology versus Displacement per Atom (DPA) was determined in addition, it used the Monte Carlo Neutron Transport simulation MCNP6 and SRIM codes for estimation of DPA. In this work, among the most important results obtained from experimental and simulation methods, it was found that: resistivity and RMS increased with an increasing DPA, this phenomenon occurred after neutron irradiation. The experimental results show good agreement with the simulation data. Furthermore, the enhancement of irradiation times leads the resistivity values to attain saturation. This later reaches a stability value above 11 × 1016 Displacement /cm3 between 0.74 and 3.96 × 1018n/cm2.

Neutron screen method for axial uniformity in silicon ingots for neutron transmutation doping at WWR-K reactor

In 2017, Institute of Nuclear Physics and Chiyoda Technol Corporation signed agreement on cooperation in research and development of technology for neutron-transmutation doping of large-sized silicon with a diameter of more than 6 in. and a height of up to 500 mm for the WWR-K reactor.The goal of the study is to reduce an irregularity in the electrical resistivity over the volume of the silicon ingot to (3–4)%. In view of reduction of the height irregularity factor, thermal neutron-absorbing materials are used, whereas an electric motor, which provides rotation of silicon ingot around its axis, is used to reduce the radial irregularity. The object of investigation is an aluminum block, which is a model of silicon ingot.This work presents the obtained at the critical facility results of the study the application of the screen method to the reduction of the height irregularity for doping in large-size silicon ingots.

An analytical model for electronic noise in a cryogenic bolometer detector readout circuit

This paper presents an analytical model to quantify the measured noise in a cryogenic bolometer readout circuit. The model includes the contributions from the bias resistors and sensor resistors, voltage and current noise of amplifier, and cable capacitance. The model parameters are empirically estimated using frequency domain analysis of the measured noise data of indigenously developed Neutron Transmutation Doped (NTD) Ge sensors. The model is shown to describe noise data for NTD Ge sensorsover a wide range of resistances corresponding to temperatures in the range 20–70 mK.Relative contributions of different components are discussed and it is shown that the contribution to the overall noise from the differential amplifier at 300 K is the dominant source. It is observed that the amplifier flicker noise is significantly lower than that specified in the amplifier datasheet. The present study also indicates that a desirable value of resistance of NTD sensor (R NTD) from noise considerations is ≲ 1 GΩ at ∼ 20 mK.

Selective thermal neutron transmutation doping with Gd masks in GaN semiconductors

For the first time, selective neutron transmutation doping was successfully performed on GaN through Gd masks, showing the feasibility of patternable doping through neutron irradiations. In collaborating with Oak Ridge National Laboratory, GaN with Gd masks was irradiated by directional neutrons. By using the Gd properties with high neutron absorption cross-sections, it was confirmed that the area covered by Gd masks on GaN was completely shielded from neutrons, and the uncovered area was doped with the generated Ge and 14C. Property differences were clearly identified in various ways when comparing the area exposed by neutrons and the area unexposed by neutrons. The discoloration by the ejected protons and elastic scattering of neutrons appeared only in the exposed area while the unexposed area remained the same as before irradiation. The aspect ratio of the patterned profile of GaN was estimated by comparing patterns on the front and backside. From energy dispersive X-ray spectroscopy spectra and secondary ion mass spectrometry measurement, the concentration difference between Ge and 14C as well as the exact concentration of produced 14C was also checked. Schottky barrier diodes on the selectively doped GaN were fabricated and investigated to study the electrical properties.

COMPUTATIONAL STUDY OF RADIATION CHARACTERISTICS IN THE NICHE OF THE EXPERIMENTAL DEVICES OF THE WWR-K REACTOR

A nuclear reactor is a complex engineering and technical installation that generates radiation. Because of this, the experimental measurement of the radiation characteristics of a nuclear reactor is a difficult task, and in some cases technically impossible. The modern development of calculation codes and tools makes it possible to determine the radiation characteristics of a nuclear reactor with sufficient accuracy and reliability. Due to this, computational modeling of physical processes occurring in a nuclear reactor has become one of the main scientific research methods. The WWRK reactor is a multi-purpose research reactor with a large number of vertical and horizontal irradiation positions used for a wide range of scientific and applied problems. The irradiation position with the largest dimensions in the WWR-K reactor is the niche of experimental devices, which makes it possible to irradiate objects up to 1000 mm in diameter. This position is considered as a candidate for neutron transmutation doping of silicon ingots with a diameter of more than 200 mm. The article presents the radiation characteristics for the current and modernized configuration of the niche of the experimental devices of the WWR-K reactor. It is shown that the upgrade of the configuration leads to an improvement in the neutron characteristics in the irradiated position.

In-situ neutron-transmutation for substitutional doping in 2D layered indium selenide based phototransistor

Neutron-transmutation doping (NTD) has been demonstrated for the first time in this work for substitutional introduction of tin (Sn) shallow donors into two-dimensional (2D) layered indium selenide (InSe) to manipulate electron transfer and charge carrier dynamics. Multidisciplinary study including density functional theory, transient optical absorption, and FET devices have been carried out to reveal that the field effect electron mobility of the fabricated phototransistor is increased 100-fold due to the smaller electron effective mass and longer electron life time in the Sn-doped InSe. The responsivity of the Sn-doped InSe based phototransistor is accordingly enhanced by about 50 times, being as high as 397 A/W. The results show that NTD is a highly effective and controllable doping method, possessing good compatibility with the semiconductor manufacturing process, even after device fabrication, and can be carried out without introducing any contamination, which is radically different from traditional doping methods.

Selective Thermal Neutron Transmutation Doping with Gd Masks in Gan Semiconductors

Selective Thermal Neutron Transmutation Doping with Gd Masks in Gan Semiconductors

Advanced hybrid-structured anodes for lithium-ion batteries

Silicene is an artificially created two-dimensional silicon crystal with a hexagonal structure. Silicene layered product on a metal substrate is considered as the promising anode material for a lithium ion battery (LIB). The creation of polyvacancies in silicene can significantly reduce the charging time of the anode, and hence the entire battery, as well as increase the charging capacity of the device. However, the presence of polyvacancies reduces the mechanical strength of silicene. To strengthen defective silicene and increase its intercalation ability, it is proposed to carry out neutron transmutation doping of this two-dimensional material together with the substrate. In this work, the molecular dynamics method is used to study the strength of the doped and undoped two-layer silicene on a Ni(111) substrate when the interlayer space is filled with lithium. The morphology of silicene intercalated with lithium and the detailed structure of the lithium packing are investigated. The stresses appearing in the walls of the silicene channel when it is filled with lithium are calculated. A direct comparison of the properties characterizing the suitability of the two-layer silicene as a LIB anode is carried out for the corresponding doped and undoped systems.

A new neutron transmutation doping system for radial irradiation uniformity

A new neutron transmutation doping system for radial irradiation uniformity

Conceptual Design of Experimental Facility for Large-Diameter NTD-Si at the IRT-T Reactor

The IRT-T reactor has been conducting research in the field of irradiation of ingots of single-crystal semiconductor materials since 1987. The article describes the existing silicon doping facility. The results of studies on the possibility of creating an additional irradiation channel for neutron-transmutation doping of silicon are presented. It is shown that the use of a graphite reflector and a thermal neutron filter based on boron makes it possible to achieve non-uniformity of irradiation up to 5 %. The principal possibility of irradiating single-crystal silicon ingots with a diameter of up to 203 mm and a length of up to 500 mm is shown. The questions of optimizing the configuration of the core and the regime of reactors operation for increasing the neutron flux in the irradiation channels are discussed. In addition, applying the facility to produce base materials for neutron dosimeter in neutron capture therapy studies is proposed.

Improvement of Semiconductors Quality Using Isotopic Nanoengineering

The article covers a solution of a modern electronics problem: improvement of data transmission device speed using the example of fiber-optic communication lines (FOCL). The data processing rate and throughput of transmission channels are determined by capabilities of the optoelectronics and, first of all, by the performance of its hardware components. The article presents all possible ways to improve the performance of FOCL. Design and production of communication devices moves to the nanotechnological level that opens up new possibilities for creation of semiconductors with advanced characteristics. The methods and means chosen for production of the nanostructures are crucial for creation of the new generation hardware components. Graphene is considered as the most promising material for creation of the new generation hardware components for semiconductors. Potential capabilities of the material are not yet fully explored. Isotopic nanoengineering is used as the method for production of the nanostructures with improved characteristics. In particular, we use the neutron transmutation doping technology based on irradiation of a graphite sample with a neutron flux. This method increases content of the 13C isotope (natural graphite contains only about 1.1% of this isotope). As a result, the band gap opens bringing the properties of the material closer to the properties of a semiconductor. The closer the width of the graphene band gap to the width of the silicon band gap, the closer the properties of graphene to the properties of semiconducting silicon. Furthermore, all properties of the natural graphite (high throughput and sensitivity to almost the entire optical spectrum) are preserved.

Electronic Properties of Silicene Films Subjected to Neutron Transmutation Doping

The radiation doping of single-crystal silicon with phosphorus retains the structure of the sample, reduces internal stresses, and increases the lifetime of minority charge carriers. The study is concerned with the effect of phosphorus additives on the electronic properties of silicene. The electron density-of-states spectra of a phosphorus-doped single layer and 2 × 2 bilayer silicene on a graphite substrate are calculated by the quantum-mechanical method. The carbon substrate imparts semiconductor properties to silicene due to p–p hybridization. Doping with phosphorus can retain or modify the metal properties gained by silicene. The position of phosphorus dopant atoms in silicene influences the semiconductor–conductor transition. The theoretical specific capacity of a phosphorus-doped silicene electrode decreases, and the electrode becomes less efficient for application in lithium-ion batteries. However, the increase in the conductivity is favorable for use of this material in solar cells.

Conceptual design of irradiation device for silicon neutron transmutation doping around Es-Salam research reactor

Silicon neutron transmutation doping remains one of the most viable nuclear applications for research reactors. Providing this kind of product involves an irradiation method capable of fulfilling the quality requirements of doping and alleviating the challenges related to the design and safety of the irradiation device. In this paper, we propose an irradiation device prototype for neutron transmutation doping of silicon ingots with diameters of 2 to 3 in. based on the Es-Salam research reactor. The thermal hydraulic analysis of the proposed irradiation device was performed to determine the optimum conditions for cooling. The effect of the mechanical vibrations induced by the circulation of coolant in the device was quantified via experimental measurements under different flow rates. The results show that the maximum temperature reached by the silicon ingots is below the temperature limit, effectively validating the design of the irradiation device. Other investigations are prospected to further optimize the design and the irradiation conditions. The irradiation of silicon ingots with a large diameter will be considered.

New Compact Neutron Generator System for Multiple Applications

Compact neutron generators can provide a high flux of neutrons with energies ranging from thermal (0.025 eV) to 14 MeV. The application of the deuterium-deuterium, D-10B, and D-7Li nuclear reactions and new advancements in high-flux neutron generator technology along with the commercial availability of high-voltage direct current power supplies enables the production of high-flux 2.45-, 6-, 10-, and 13-MeV neutrons. The high-energy neutrons or the moderated epithermal neutrons from the new compact neutron generator can greatly advance cancer therapy, radioisotope production, neutron yield measurement, special nuclear materials detection, and neutron transmutation doping of silicon.

Promising Neutron Irradiation Applications at the High Temperature Engineering Test Reactor

Abstract The high temperature gas-cooled reactor (HTGR) has advantages for irradiation applications such as large space available for irradiation at reflector region and high thermal neutron spectrum with the graphite moderator. High temperature engineering test reactor (HTTR), a prismatic type of the HTGR, has been constructed to establish and upgrade the basic technologies for the HTGRs. Many irradiation regions are reserved in the HTTR to be served as a potential tool for an irradiation test reactor in order to promote innovative basic researches such as materials, fusion reactor technology, and radiation chemistry. This study shows the overview of some possible irradiation applications at the HTTRs including neutron transmutation doping silicon (NTD-Si) and Iodine-125 (125I) productions. The HTTR has possibility to produce about 40 tons of doped Si-particles per year for fabrication of spherical silicon solar cell. Besides, the HTTR could also produce about 1.8 × 105 GBq/yr of 125I isotope, comparing to 3.0 × 103 GBq of total 125I supplied in Japan in 2016.

Estimation of Residual Radioactivity and Radiation Damage in SiC After Neutron Irradiation

In the process of neutron transmutation doping (NTD), Si, C, and impurities in the SiC become radioactive nuclides by neutron capture reaction (n, $\gamma $ ) and several threshold reactions. The radiations emitted from the residual radionuclides constantly damage the SiC until they completely decay. The radiation damage can create many defects in the SiC, and the defects can reduce the electron mobility and distort the band structure. This radiation damage to the SiC should be evaluated in terms of quality management. In order to quantify the sources of radiation damage, time variations of the residual radionuclides’ radioactivity in 5-in cylindrical SiC ingot after neutron irradiation were calculated using the DCHAIN program linked to the particle and heavy ion transport code system (PHITS). In the calculation, it was assumed that the SiC ingot was irradiated in the NTD1 irradiation hole of the High-Flux Advanced Neutron Application Reactor (HANARO) at the Korea Atomic Energy Research Institute (KAERI). The energy spectrum of neutrons in the HANARO NTD1 irradiation hole calculated by using the Monte Carlo N-particle code version 6.1 (MCNP6.1) code was considered as a neutron source for the calculation. Based on the radioactivity data, the total flux and energy spectra of the electrons and gamma-rays in the SiC were calculated to analyze the properties of the radiation sources. Most of the radiations were emitted from the beta decay of 31Si, but they decayed early, and radionuclides with a relatively long half-life, such as 59Fe and 32P, became the major radiation sources. Finally, the radiation damage was calculated in the displacement per atom (DPA) unit. The time variations of the DPA rate and cumulative DPA in the SiC are presented.

Use of Neutron Absorbers to Influence the Neutron Transmutation Doping Process in Silicon

Neutron transmutation doping is used to create high-quality silicon with a specific target resistivity. By implementing neutron absorbers, it is possible to obtain a broader range of postirradiation resistivities. To develop this method, the influence of neutron absorbers on the reactor spectrum in Belgian Reactor 1 was numerically simulated and experimentally verified. A comparison between the modeled reactor spectrum and the spectrum obtained through activation foils showed good agreement. These data were used to calculate the resistivity of silicon under cadmium and hafnium foils with different thicknesses after neutron irradiation. Experimental four-point probe measurements confirmed the calculated resistivities. Hence, the research shows that tailoring the reactor spectrum using neutron absorbers allows for a large range of final resistivities or doping concentrations in silicon during a single irradiation cycle.