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Since it is proved that neutrino has non-zero mass, many research groups are searching for neutrinoless double beta decay to find the mass and type (Dirac or Majorana) of neutrino. Advanced Molybdenum based Rare process Experiment (AMoRE) collaboration is one of the international groups. 100Mo is selected for the AMoRE as a source isotope of 0νββ decay because of its relatively high Q-value. The CaMoO4 crystals what we are used for the detector elements since they show brightest scintillation light among variety of molybdate crystals at room and cryogenic temperature. In order to avoid background events distributed by 2νββ of 48Ca and raise the detection efficiency, 40Ca100MoO4 crystal had developed.
External muon background is decreased in underground laboratory. On the other hand, internal isotopes, especially 208Tl, 212Bi, 212Po, 214Bi, 214Po, and 88Y+ 88Zr could make a serious problem that those nuclides could make events on 3 MeV region. For preventing this, FOMOS-Materials Inc. in Russia grows 40Ca100MoO4 crystals with their techniques for low internal radioactive background, and then I check the level of internal background and feedback the result to them. I ran this experiment in Yangyang underground Laboratory (Y2L) which is located in 700 m underground. Data are analyzed by time-amplitude analysis and previous events selection method to select out alpha signals only. Time difference analysis method is effective on short half-life isotopes. So I chose 214Po, 215Po, and 216Po in U/Th decay chain to analyze. Among three enriched 40Ca100MoO4 crystals, SS68 has best quality in transmittance and low activities. It satisfied the radioactivity goal of AMoRE-10.
Thesis Advisor: Prof. Hongjoo Kim