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

Application of a large-volume NaI scintillator to search for the cold dark matter (DM) in the Universe is discussed. A low-noise (∼5 keV) and low-background (∼5/keV kg day) were achieved even with a large (36.5 kg) NaI scintillator. Light output efficiencies for ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ and ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$ were measured as 0.4±0.2 and 0.05±0.02, in the recoil energy range of 5–100 keV and 40–300 keV, respectively. NaI is shown to have merits of a large volume, large scattering cross sections for dark matter, and of 100% abundance of finite-spin nucleus, but to have the demerits of a small form factor due to the finite-size effect of ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$ at the presently measured energy region.