Application of a large-volume NaI scintillator to search for dark matter

Bulk Organic-Inorganic Methylammonium Lead Halide Perovskite Single Crystals for Indirect Gamma Ray Detection

Scintillators that convert ionization radiation photons to UV-visible photons have attracted extraordinary attention. Traditional scintillators are associated with a vacuum photomultiplier tube that faces strict constraints of fragility, magnetic fields, and operated voltage, or coupled to a silicon photomultiplier (SiPM) with optical silicone grease. Here, we report a high-performance radiation detector with an indirect photon-to-photon conversion radiation detection model based on perovskite single crystals (SCs), where perovskite SCs have been directly integrated into the window of SiPM by using the solution growth method at low temperature. Tunable X (γ)-ray excited light emission in the range of 414 to 600 nm is obtained with different concentrations of Br doping, which greatly matches the response wavelength of SiPM. Small Br-doped CH₃NH₃PbBr_0.05Cl_2.95 SCs exhibit high transmittance and weak self-absorption, resulting in improved scintillation light emissions. Moreover, we have successfully collected a ¹³⁷Cs source gamma-ray pulse height spectrum with the SiPM readout. The MAPbBr_0.05Cl_2.95 scintillator exhibits a decay time of 0.14 ± 0.02 ns and a light yield of 18 000 photons/MeV with an energy resolution of 10.5 ± 0.4% at 662 keV. The results indicate that the CH₃NH₃PbBr_xCl_3-x perovskite SCs could enable the next generation of low-cost, fast, and fine-energy resolution scintillators.

Effect of thallium impurities in the DAMA experiment on the allowed parameter space for inelastic dark matter

The inelastic dark matter scenario was proposed to reconcile the DAMA annual modulation with null results from other experiments. In this scenario, weakly interacting massive particles (WIMPs) scatter into an excited state, split from the ground state by an energy δ comparable to the available kinetic energy of a galactic WIMP. We note that for large splittings δ the dominant scattering at DAMA can occur off of thallium nuclei, with A∼205, which are present as a dopant at the 10(-3) level in NaI(Tl) crystals. For a WIMP mass mχ≈100 GeV/c2 and δ≈200 keV, we find a region in δ-mχ-parameter space which is consistent with all experiments. These parameters, in particular, can be probed in experiments with thallium in their targets, such as KIMS, but are inaccessible to lighter target experiments. Depending on the tail of the WIMP velocity distribution, a highly modulated signal may or may not appear at CRESST-II.