Development of Low Radioactive Molecular Sieves for Ultra-Low Background Particle Physics Experiment

This study develops low radioactive molecular sieves (MS) for ultra-low background particle physics experiment. The manufactured MS is of type 4A. $^{226}$Ra and $^{232}$Th have concentrations of about 57 and 198 mBq/kg, respectively, measured by applying high-purity germanium (HPGe) measurement. The reduction of the radioactivity from the commercial one is about 99 and 97 percent for $^{226}$Ra and $^{232}$Th, respectively. Furthermore, the radon emanation rate from MS filter is about 2.1 mBq, which is measured by utilizing pin-photo type radon detector. This developed MS is expected to remove the impurity from the noble gas, in which low radioactivity is needed such as dark matter search experiment.