High flux of electron neutrinos(${\nu }_{\mathrm{e}}$) is produced at nuclear power reactors through the decays of nuclei activated by neutron capture. Realistic simulation studies on the neutron transport and capture at the reactor core were performed. The production of ${}^{51}\mathrm{C}\mathrm{r}$ and ${}^{55}\mathrm{F}\mathrm{e}$ give rise to monoenergetic ${\nu }_{\mathrm{e}}$’s at Q-values of 753 keV and 231 keV and fluxes of $8.3\times {10}^{-4}$ and $3.0\times {10}^{-4}{\nu }_{\mathrm{e}}/\mathrm{fission}$, respectively. Using data from a germanium detector at the Kuo-Sheng Power Plant, we derived direct limits on the ${\nu }_{\mathrm{e}}$ magnetic moment and the radiative lifetime of ${\mu }_{\nu }<1.3\times {10}^{-8}{\mu }_{\mathrm{B}}$ and ${\tau }_{\nu }/{\mathrm{m}}_{\nu }>0.11\mathrm{s}/\mathrm{eV}$ at $90\%$ confidence level (CL), respectively. Indirect bounds on ${\tau }_{\nu }/{\mathrm{m}}_{\nu }^3$ were also inferred. The ${\nu }_{\mathrm{e}}$-flux can be enhanced by loading selected isotopes to the reactor core, and the potential applications and achievable statistical accuracies were examined. These include accurate cross-section measurements, studies of mixing angle ${\theta }_{13}$ and monitoring of plutonium production.

The millicharged particle has become an attractive topic to probe physics beyond the Standard Model. In direct detection experiments, the parameter space of millicharged particles can be constrained from the atomic ionization process. In this work, we develop the relativistic impulse approximation (RIA) approach, which can duel with atomic many-body effects effectively, in the atomic ionization process induced by millicharged particles. The formulation of RIA in the atomic ionization induced by millicharged particles is derived, and the numerical calculations are obtained and compared with those from free electron approximation and equivalent photon approximation. Concretely, the atomic ionizations induced by mllicharged dark matter particles and millicharged neutrinos in high-purity germanium (HPGe) and liquid xenon (LXe) detectors are carefully studied in this work. The differential cross sections, reaction event rates in HPGe and LXe detectors, and detecting sensitivities on dark matter particle and neutrino millicharge in next-generation HPGe and LXe based experiments are estimated and calculated to give a comprehensive study. Our results suggested that the next-generation experiments would improve 2-3 orders of magnitude on dark matter particle millicharge δ_χ than the current best experimental bounds in direct detection experiments. Furthermore, the next-generation experiments would also improve 2-3 times on neutrino millicharge δ_ν than the current experimental bounds.

An important background to the liquid argon detectors is that they are caused by the diffusion of radioactive isotopes in a scintillator (liquid phase). This radioactive isotope is produced in argon’s surrounding devices, such as circulation pipelines and liquid argon containers. The solid argon as a scintillation material in the detector can inhibit the diffusion and drift of radioactive isotopes in a solid phase scintillator. Additionally, the structure of a solid argon detector is simple and reduces the total source of radioactive background. In the CDEX-300 detection system, solid argon could substitute for liquid argon as the veto detector, preventing radioactive isotopes drifting to the central main detector (HPGe detectors array) surface to reduce backgrounds. Therefore, solid argon has great potential in the experiments since it is especially helpful to get the lower background in a larger active volume than liquid argon required in those low background detection experiments. This work introduces the preparation process and device of the large volume transparent crystalline argon, the acquisition of scintillation light, and the pulse amplitude spectrum of ¹³⁷Cs obtained from a prototype detector of transparent solid argon crystal. The results show that the scheme proposed in this study can successfully produce a large volume transparent crystalline argon detector, the scintillation light signals can be effectively obtained from the solid argon scintillator, and the corresponding pulse amplitude spectrum is given. This work indicates that it is feasible to develop a solid argon crystal scintillation detector by using our approach.