A method for depositing actinides directly onto a 4H-SiC Schottky barrier diode (SBD) detector as a field deployable actinides sensor was developed to enable off-site analysis, shortening the time to obtain critical information such as elements, concentration, and/or isotopic ratio related to the radiological situation. A thin film of Hg was first electrodeposited onto the Pt contact of the SiC diode, followed by chronoamperometric deposition of microgram levels of actinides under conventional control conditions. The 4H-SiC diode maintained consistent functionality through the electrodeposition process and showed resolved alpha-energy spectra that contained accurate isotopic information demonstrating the feasibility of a combined chemical and radiological sensor for field actinide detection and quantification.

In a paper titled “NIXE: Neutron Depth Profiling coupled with Particle Induced X-ray Emission,” Albarqi, et al. [1] proposed a modification of the Neutron Depth Profiling (NDP) technique to use the charged particle induced X-ray (PIXE) emission generated from the energetic ions produced during nuclear reactions of the NDP process to provide additional information about the depth profile of elements near the surface of a material. This paper applies a more comprehensive analysis of the concept using the Geant4 Monte Carlo code. The results of this analysis show that the approach may be possible and produces benefits such as depth concentration for elements beyond traditional NDP. However, suppression of typical low-energy background noise is critical and would limit which NDP facilities can perform the NIXE technique. The data in this paper can inform the planning of such experiments.

This paper describes a molecular plating method in which americium-241 (Am-241) was directly deposited onto a 4.8 mm x 4.8 mm Schottky electrode of 4 H-SiC devices. The plating solution consists of isopropanol and dilute nitric acid. Plating was conducted for one hour using a high voltage between 300 and 600 V to plate the radionuclide. A gasket with an aluminized mylar contact surface was added to a traditional disposable electrodeposition cell to accommodate the small size of the diode. Deposition recoveries of 50–65% have been consistently achieved using 20–30 nCi of Am-241 with minimal damage to the diode surface.

A protective covering is often required for neutron depth profiling (NDP) measurements of sensitive materials (e.g., Li-ion batteries). Addition of this layer can increase NDP profile energy broadening and depth assignment uncertainty. This study evaluates the magnitude of these effects when polyimide films of variable thicknesses are placed over Li-rich solids. Key results include a modeled increase in cold neutron beam attenuation with increased film thickness, a methodology for estimating profile energy broadening using a sigmoidal function, and, when using a thick layer, that the broadening will add uncertainity to the zero-depth position and depth scale assignment.

Silicon carbide (SiC) and gallium nitride (GaN) semiconductors are two detector candidates for high flux neutron monitoring entailing high temperature and high radiation environments owing to their wide band gap and high resistance to radiation damage. While the neutron elastic scattering with carbon (C) and silicon (Si) makes SiC intrinsically sensitive to neutrons, neutron interaction with nitrogen (N) by way of 14N(n,p)14C reaction provides neutron sensitivity to GaN. In this study, we investigated reactor-based high flux neutron monitoring with in-house fabricated SiC detectors and studied the feasibility of neutron detection using GaN. As proof-of-concept for GaN neutron sensitivity, we evaluated SiC detectors coupled with nitrogen based (N-based) neutron converter materials, and commercially purchased AlGaN photo sensors. Spectral response as well as raw waveform data from SiC, SiC coupled with N-based converter layers, and AlGaN sensors were acquired while exposing the detectors to a mixed neutron–gamma field of a research reactor at ex-core locations at various power levels. The experimental SiC detector spectra were compared against Geant4 Monte Carlo (MC) simulations, which agreed with the measurement results. The reactor power determined using SiC detector raw data correlated well with that indicated by a standard compensated ion chamber (CIC). The AlGaN sensors showed promising results with a correlation between sensor response and reactor power. The current study demonstrates SiC as a suitable detector for high flux neutron monitoring with good radiation tolerance based on near-core irradiation.

Prompt gamma-ray activation analysis facilities with high neutron currents (≥109 s−1) generate triton-induced fast neutrons from 6Li-loaded collimators and beam stops at rates that damage gamma-ray detectors. We develop an alternative beam stop design using 3He gas that produces negligible gamma-ray and fast-neutron background following neutron absorption. Replacing a 6Li glass beam stop with a test cell containing 2.5 MPa cm of 3He reduced fast neutron production by 73 %. An optimal 3He beam stop design with a 100-µm-thick entrance window, modeled using MCNP6, enables operation of detectors closer to the beam stop.

Rechargeable Li-ion batteries (LIBs) are an indispensable technology in modern life for efficient energy storage; they are deployed in large numbers and operate close to their electrochemical stability limits. Detrimental reactions at battery electrodes can cause capacity fade and even catastrophic failures, hindering the widespread use of LIBs, particularly in mobile power energy solutions such as all-electric vehicles. It is valuable to visualize the distribution and flow of the active element, lithium, in electrodes for better diagnosis of battery functioning and failure. Specifically, to address issues of the degradation of electrodes and growth of Li metal dendrites, the neutron depth profiling (NDP) technique was applied with two dimensional (2D) pinhole aperture scans to spatially map lithium in 3D. NDP is a neutron activation analysis method used to quantitatively measure the abundance and depth distribution of several technologically important elements (Li, B, N, He, Na, etc). The technique has been used to measure the Li distribution in modern battery technologies based on the nuclear reaction, 6Li + n → a (2055 keV) + 3H (2727 keV). Charged a and triton (3H) particles lose kinetic energy during transport through the specimen media, which is measured to determine the depth of the activation reaction. The normalized counts of activation events are recorded to determine the abundance of Li at the corresponding depth. The method has been applied to measuring the spatial distribution of Li in two LixFePO4 electrode films. Because NDP is sensitive only to the 6Li isotope of Li, which has a natural isotope abundance of 7.5 at%, isotope enrichment of LFP was used to greatly improve mapping efficiency. Two electrodes were prepared, one with a single charge/discharge cycle and the other with 5532 cycles, denoted as LFP1 and LFP5k, respectively. It was shown that the Li concentration is high and homogeneous in LFP1, with x = 0.65 ± 0.06 and Li concentration variation of 9%, where that in LFP5k much lower and spatial distribution much more heterogeneous, with x = 0.38 ± 0.05 and Li concentration variation of 13%. The significant capacity decay in the LFP5k electrode is discussed in the context of structural changes in electrode materials due to electrochemical processes. The nature of Li dendritic growth in polymeric electrolytes has also been investigated. A symmetric sandwich cell of Li / poly(ethyleneoxide) (PEO) : lithium bis(trifluoromethane)sulfonamide (LiTFSI) / Li was used to as a model system in this study. In situ NDP measurements has been carried out during directional Li pumping from the bottom Li electrode to the top at a constant electric current of 0.1 mA. After a period of steady Li plating, dendrites start to grow, and eventually short-circuit the polymer electrolyte. Li mapping studies reveal rather heterogeneous lateral distribution of Li over length scales from below a millimeter to centimeters. The lateral mobility of Li appears to be large and the deposited Li layer on top electrode partly deform from its original circular shape. Most Li in the electrolyte layer resides in dendrites growing from the top electrode, with overall composition decrease linearly from the electrode interface to the bulk of the electrolyte. It is observed that dendrites also grow from the bottom electrode, where presumably only Li oxidation reaction occurs. The revelation poses new design and engineering challenges in using Li metal electrode in future batteries. Figure 1

Boron is used widely in thin-film solid-state devices for neutron detection. The film thickness and boron concentration are important parameters that relate to a device׳s detection efficiency and capacitance. Neutron depth profiling was used to determine the film thicknesses and boron-concentration profiles of boron carbide-based polymers grown by plasma enhanced chemical vapor deposition (PECVD) of ortho-carborane (1,2-B10C2H12), resulting in a pure boron carbide film, or of meta-carborane (1,7-B10C2H12) and pyridine (C5H5N), resulting in a pyridine composite film, or of pyrimidine (C4H4N2) resulting in a pure pyrimidine film. The pure boron carbide film had a uniform surface appearance and a constant thickness of 250nm, whereas the thickness of the composite film was 250–350nm, measured at three different locations. In the meta-carborane and pyridine composite film the boron concentration was found to increase with depth, which correlated with X-ray photoelectron spectroscopy (XPS)-derived atomic ratios. A proton peak from 14N (n,p)14C reaction was observed in the pure pyrimidine film, indicating an additional neutron sensitivity to nonthermal neutrons from the N atoms in the pyrimidine.

This paper reports the observable effects of induced radiation on lithium-ion batteries when electrochemical cells are exposed to γ-irradiation at dose up to 2.7 Mrad. A visual discoloration is noted at post-irradiation and chemical changes in the electrolyte solution are determined by Fourier transform infrared spectroscopy. While battery degradation is noted in this study upon the applied gamma dose, the battery characterized by neutron depth profiling for Li quantification will only receive gamma dose at a fraction of Rad to a few Rad, depending on the irradiation time. This finding established a threshold beyond which the battery’s performance maybe affected and concluded that the neutron-based method is nonintrusive and does not affect the fidelity of the acquired data.

The neutron depth profiling technique based on the neutron activation reaction, 6Li (n, α) 3H, was applied with two dimensional (2D) pinhole aperture scans to spatially map lithium in 3D. The technique was used to study model LiFePO4 electrodes of rechargeable batteries for spatial heterogeneities of lithium in two cathode films that had undergone different electrochemical cycling histories. The method is useful for better understanding the functioning and failure of batteries using lithium as the active element.

The origin of the relaxor behavior in ${\mathrm{K}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}{\mathrm{TaO}}_{3}\phantom{\rule{0.28em}{0ex}}(\mathrm{KLT})$ and other disordered perovskites is now recognized to be due to the reorientation of the polar nanodomains formed by the correlated dipoles of off-center ions. The collective dynamics of these systems evolve through several temperature stages. On decreasing temperature below the so-called Burns temperature ${T}_{B}$, individual dipoles become correlated within nanosized regions. On further cooling, the slow dynamics of these polar regions allows local lattice distortions to take place and the formation of polar nanodomains at ${T}^{*}l{T}_{B}$. At still lower temperature, some relaxors undergo a phase transition while others do not. In KLT, there is a critical Li concentration ${x}_{c}=0.022$ above which the system undergoes a structural transition at ${T}_{c}$, and below which it freezes in a dipole glass state at ${T}_{f}$. To better understand the nature of this critical concentration, the changes that occur upon crossing it and the nature of the dipole glass state, the collective dynamics of KLT have been studied by dielectric spectroscopy and neutron diffraction for two Li concentrations $(x=0.026$ and $0.018)$, close to but straddling the critical concentration ${x}_{c}$. Two very different transitional behaviors are observed. Just below this critical concentration, KLT displays critical slowing down and the onset of freezing as seen in hydrogen-bonded molecular ferroelectrics, while just above this concentration, KLT undergoes a first-order structural transition.

This paper presents a Monte Carlo code to get response spectrum of ions for the Neutron Depth Profiling (NDP) technique called Monte Carlo NDP (MC-NDP) that simulates the behavior of ions transmitted through a sample matrix and generates the energy spectrum for a specified detector. The MC-NDP model is based on the Ziegler–Biersack–Littmark Model, but incorporates the advantages of TRIM and CORTEO. The Impulse Approximation method is used to determine the flight length with the indexical interpolation method rather than the Magic algorithm for the scattering angle between ions and nucleus. This makes MC-NDP more efficient and convenient to simulate entire ion histories by a Monte Carlo approach. MC-NDP’s results agree well with both TRIM results and the experimental data.

Measuring the distribution of lithium in high capacity lithium-ion battery (LIB) electrodes is essential to understanding the coulombic losses during the lithiation/delithiation processes that occur while charging and discharging the cell. In this research, two half-cell prototypes were fabricated by electrochemically lithiating Sn foil anodes in 1M LiBF4 in a 1:1 (wt:wt) ethylene carbonate and dimethyl carbonate solutions at a constant potential of 0.50 and 0.67 V (vs. Li/Li+). The neutron depth profiling (NDP) technique was employed to study the Li distributions in the anodes. Li concentration profiles were resolved for the samples lithiated under different conditions for LIB studies. In addition, this paper demonstrated an in situ NDP measurement of an electrochemical cell with a thin window design, which reveals the dynamics of lithium distribution within the Sn anode.

Neutron depth profiling (NDP) makes accessible quantitative information on a few isotopic concentration profiles ranging from the surface into the sample a few micrometers. Because the candidate analytes for NDP are few, there is little interference encountered. Furthermore, neutrons have no charge so mixed chemical states in the sample are of no direct concern. There are a few nuclides that exhibit large probabilities for neutron scattering. The effect of neutron scattering on NDP measurements has not previously been evaluated as a basis for either enhancing the reaction rates or as a source of measurement error. Hydrogen is a common element exhibiting large neutron scattering probability found in or around sample volumes being analyzed by NDP. A systematic study was conducted to determine the degree of signal change when neutron scattering occurs during analysis. The relative signal perturbation was evaluated for materials of varied neutron scattering probability, concentration, total mass, and geometry. Signal enhancements up to 50% are observed when the hydrogen density is high and in close proximity to the region of analysis with neutron beams of sub thermal energies. Greater signal enhancements for the same neutron number density are reported for thermal neutron beams. Even adhesive tape used to position the sample produces a measureable signal enhancement. Because of the shallow volume, negligible distortion of the NDP measured profile shape is encountered from neutron scattering.

1Institute forMaterial Research and Department of Mechanical Engineering, State University of New York, Binghamton, NY 13902 2Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 3NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899 4Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 5Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742 *email: wangh@binghamton.edu