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We report on the acquisition and modeling of the transient response of a commercial silicon (Si) solar cell using a benchtop pulsed X-ray source. The solar-cell transient output to the X-ray pulses was acquired under the dark and steady-state light illumination to mimic the practical operation of a solar cell under different light illumination levels. A solar-cell circuit model was created to develop a fundamental understanding of the transient current/voltage response of solar cell at read-out circuit level. The model was validated by a good agreement between the simulation and experimental results. It was found that the solar-cell resistance ( $R$ ) and capacitance ( $C$ ) depend on the light illumination, and the resulting variation in $RC$ time constant significantly affects the solar-cell transient response. Thus, the solar cell produced different transient signals under different illumination intensities in response to the same X-ray pulse. The experimental data acquired in this work proves the feasibility of using solar panels for prompt detection of nuclear detonations, which also builds a practical mode of X-ray detection using a low-cost self-powered detector.

In this study, we evaluated the feasibility of applying solar photovoltaic (PV) panels as sensors of nuclear and electromagnetic radiation that includes neutrons, x-rays and gamma-rays, and optical radiation emanating from a nuclear explosion. We investigated the steady-state and transient response of both a commercial silicon (Si) and a perovskite solar cell to different radiation types. Solar cell current-voltage characteristics and short-circuit current (I sc ) response under steady-state x-ray illumination were measured. The fast transient radiation pulse from a nuclear detonation was mimicked by using a fast switching, nanosecond pulsed laser source and the transient response of the solar cells was captured on an oscilloscope. Subsequently, the transient response of Si solar cells to pulsed x-rays generated by a mechanical x-ray chopper was measured. A 2 MeV neutron beam chopper was built at the fast neutron beam facility of a research reactor to produce time-modulated neutrons and evaluate the solar cell transient response to a neutron pulse. Our steady-state measurements demonstrated good response of solar cells to x-rays and neutrons. The pulsed radiation measurements indicated that the solar cells are able to detect a fast transient radiation and produce a proportional measurable output signature.

The Ohio State University Research Reactor's (OSURR) fast neutron beamline is aimed to meet the growing demand for high flux and well-collimated neutron sources for fast neutron radiography and tomography applications. The beam facility consists of two collimators, separated by a neutron-gamma shutter, and a movable beam stop, sitting on a rail system for back/forth and up/down motion to provide an adjustable working space. The beam facility provides a beam diameter of 3.2-cm and has a calculated geometric L/D ratio of ~62. The collimator closer to reactor core includes a 10.16-cm thick polycrystalline Bismuth for filtering gamma-rays, which provides ~2 orders of magnitude reduction in gamma flux at 2-MeV, and a 15.24-cm thick graphite with a 3.2-cm diameter aperture. Various Monte Carlo N-Particle (MCNP) simulations were performed to obtain neutron energy spectrum, neutron and gamma flux distributions, and dose rate values. Simulations showed a fast neutron (@1.6 MeV) flux ~5.4 × 107 n·cm-2·s-1 at the collimator exit. While the simulations of neutron and gamma flux distributions have verified that the beam shutter and beam stop provide a decent neutron and gamma shielding, a neutron radiograph of the beam was experimentally obtained using a Polyvinyl Toluene (PVT) based plastic scintillator and a lens-based imaging setup which has further validated the simulated radiographs of the beam. Simulations also provided neutron dose rates around the beam stop with a close agreement with experimental values. However, disagreements were found between experimental and simulated gamma flux dose rates, which needs further validation.

The use of optical instrumentation in advanced nuclear fission systems, such as molten salt reactors, liquid metal-cooled reactors, and high-temperature gas-cooled reactors, has the potential to enhance reactor safety and economic performance through in situ and online measurement of reactor conditions. Selection of suitable optical components, such as optical windows and fibers, is essential for operation of optical instrumentation in intense radioactive and thermal environments inherent to nuclear reactor systems. We present the development and performance of a self-contained and mobile post-irradiation examination system for rapid characterization of the optical properties of materials. The instrument combines linear absorption and nanosecond Z-scan modules in a compact, relocatable design. The system mobility allows for the evaluation of optical samples at the site of irradiation, minimizing the delay between extraction from the irradiation site and optical characterization. This provides nearly real-time information on the material performance under simultaneous irradiation and thermal annealing, simulating the relevant conditions for the use of those components in nuclear power systems.