Lei Raymond Cao

The negatively charged boron vacancy (VB−) in hexagonal boron nitride (hBN) is a promising quantum defect that can be used to sense pressure, temperature, and magnetic field with high spatial resolution. hBN enriched with the boron-10 and nitrogen-15 isotopes, denoted h10B15N, has good contrast and coherence for quantum sensing because nitrogen-15 has nuclear spin (1/2), reducing hyperfine interactions. Boron vacancies can be generated by neutron irradiation, which causes the transmutation of the boron-10 isotope to lithium-7. In this study, the ancillary structural, compositional, and mechanical properties of h10B15N crystals that have been subjected to neutron irradiation fluences from 1.4 × 1016 to 8.4 × 1017 n/cm2 were thoroughly characterized. Besides creating VB−, the process also induces other defects that generate strain in the crystal lattice. In turn, the mechanical properties of these crystals change drastically. Investigated here are the visual changes, lattice integrity, composition, crystal strain, and elastic constants (C33 and C66) to assess how these characteristics change as a function of neutron fluence.

This paper presents the development of a confocal Optically Detected Magnetic Resonance (ODMR) system to study diamond and Silicon Carbide (SiC) for reactor dosimetry and quantum defect analysis. Initially, Nitrogen-Vacancy (NV) centers in diamond were characterized to establish a performance baseline, followed by plans to map and quantify color center populations in SiC crystals before and after alpha and neutron irradiation. By correlating ODMR data with electrical performance metrics, we aim to optimize fabrication and annealing protocols to investigate fast neutron sensitivity. The ODMR system, integrated with a home-built confocal microscopy setup, includes a microwave antenna, magnet, laser, objective, and advanced measurement devices such as Si-APD and Time Tagger 20 for high-resolution T2* and T2 measurements. The characterization of the instrument includes high-resolution fluorescence and ODMR spectra of NV centers in diamond, and improved resolution with confocal optics. Ongoing work focuses on correlating luminescence with reactor neutron fluence and the long-term goal is for the advancing SiC irradiation for integrated spin defect analysis.

Detection of trace amounts of environmental tritium is a challenging problem, driving the need for field-deployable systems that offer high sensitivity, selectivity, and minimal false positives. We present a technique for high-sensitivity, high-selectivity tritium measurement, which integrates metal-hydride and gas-detector concepts into a compact field-deployable tritium sensor. A hydrogen-storage metal embedded in a gas proportional counter selectively absorbs protium (¹H) / tritium (³H) which are subsequently released into the counter volume with a reduced radiation background. Ionizations induced by ³H beta particles are then measured in proportional counting mode achieving high detection efficiency. Preliminary studies conducted with palladium (Pd) thin films coated on stainless-steel substrates demonstrated ³H absorption and metal-tritide formation, followed by ³H desorption upon heating the metal-tritide. These processes were confirmed using activity concentrations measured by a commercial tritium monitor and pulse height spectra acquired from a custom-built detector.

A new approach to developing an intrinsic betavoltaic battery is demonstrated by incorporating radiation-emitting isotopes, such as tritium, directly into the perovskite materials enabling direct power harvesting. The estimated power density for tritiated perovskite is 33.15 mWg−1, compared to 3.25 mWg−1 with conventional planar source-device structure. The long-term energy release is predicted at 73.8 kWh per kg of tritiated methylammonium lead triiodide (tritiated MAPbI3 or CT3NT3PbI3) over 12.32 years. A CT3NT3PbI3 crystal was synthesized using 4.44 mCi of tritiated water. Tritium incorporation into the final perovskite device was confirmed, with an uptake ratio of (2.1 ± 0.2)% from tritiated water to MAI precursor. However, the fabricated devices did not exhibit rectifying behavior, possibly due to the unpolished surface. The I-V curve also exhibited significant hysteresis. A key challenge identified for increasing the tritium uptake ratio is to develop a high concentration tritiated water.