The Nano Imaging Tracker (NIT) is a super-fine-grained nuclear emulsion detector with excellent spatial resolution, capable of reconstructing recoil nucleus directions for track lengths as short as 100 nm, corresponding to energies of several tens of keV. By exploiting hydrogen contained within the NIT itself as a target, we are advancing neutron spectra measurements including the sub-MeV...
A precise characterization of the environmental neutron spectrum in underground laboratories is crucial for designing future large-scale detectors and improving background modelling in rare-event searches. While fast neutrons already pose a significant background, thermal neutrons are expected to gain importance due to neutron-induced activation of detector materials. Previous flux estimates...
Ag-zeolite is a zeolite modified with silver through ion exchange. Since around 2020, certain Ag-zeolites have been reported to exhibit excellent xenon adsorption in air, and since 2023, some have shown strong radon adsorption in air. Our group has been developing original Ag-zeolites since 2023 for radon removal in underground experiments, testing their performance in air, xenon, and...
Measuring radon emanation from detector materials is a key method for controlling radon contamination, a significant source of background in rare event physics experiments. Methods for measuring radon emanation are well established but have predominantly focused on the 222Rn isotope, the dominant radon isotope for these backgrounds. However, measurements of 220Rn (thoron), the second most...
In underground astrophysics experiments such as neutrino, dark matter, and double beta decay searches, it is important to use the ultra-low radioactive impurities in the material of the detectors. We have been developing the gaseous TPC with the μ-PIC (or micropattern gaseous detectors: MPGD) and optics to measure the emissivity of alpha particles from the material surface in a low radioactive...
