The amount of radioactive impurities contaminated in the detector gases is required to be kept at a very low level for rare event particle physics such as dark matter and neutrino observation experiments. Zeolite is a well-known class of materials and is one of the possible candidates for removing impurities from gases. At the same time, the amount of radioactive impurities released from the adsorbent material needs to be sufficiently small. In this paper, a development of a new ultralow radioactive zeolite as a product of the selection of ultralow radioactive materials is reported. Results on the radon emanation and impurity adsorption from argon gas measurements are also described.

CANDLES is the project to search for neutrino-less double beta decay (0νββ) of 48Ca. The observation of 0νββ will prove existence of a massive Majorana neutrino. For the 0νββ measurement, we need a low background condition because of a low decay rate of 0νββ. Now we installed the CANDLES III system at the Kamioka underground laboratory. The CANDLES III system realizes the low background condition by a characteristic structure and data analyses for background rejection. Here we report performances of the CANDLES III system.

The use of enriched $$^{48}$$Ca is expected to improve the sensitivity of $$^{48}$$Ca double beta decay measurements. We have studied the enrichment of $$^{48}$$Ca with chemical exchange isotope separation using benzo-18-crown-6-ether resin. Chromatographic migrations of the calcium adsorption band were carried out at different migration lengths, 1 m, 20 m, and 200 m, using glass columns. Separation coefficients were observed as approximately $$3 \times 10^{-3}$$. Efforts have been made towards the production of benzo-18-crown-6-ether monomer at reasonable cost for the production of crown-ether resin for the separation of $$^{48}$$Ca.

Detecting neutrino-less double beta ($0\nu \beta \beta$) decay with high-sensitivity $0\nu \beta \beta$ detectors is of current interest for studying the Majorana neutrino’s nature, the neutrino mass ($\nu$-mass), right-handed weak currents (RHCs), and others beyond the Standard Model. Many experimental groups have studied $0\nu \beta \beta$ decay with $\nu$-mass sensitivities on the order of 100 meV and RHC sensitivities on the order of 10${ }^{-9}$–10${ }^{-6}$, but no clear $0\nu \beta \beta$ signals have been observed so far in these $\nu$-mass and RHC regions. Thus, several experimental groups are developing higher-sensitivity detectors to explore a smaller $\nu$-mass region around 15–50 meV, which corresponds to the inverted hierarchy $\nu$-mass, and smaller RHC regions on the order of 10${ }^{-10}$–10${ }^{-7}$ in the near future. Nuclear matrix elements (NMEs) for $\nu$-mass and RHC processes are crucial for extracting the $\nu$-mass and RHCs of particle physics interest from $0\nu \beta \beta$ experiments. This report briefly reviews detector sensitivities and upper limits on the $\nu$-mass and right-handed currents for several current $0\nu \beta \beta$ detectors and the $\nu$-mass and RHC sensitivities expected for some near-future ones.

We have studied the neutrino-less double beta decay(0νββ) of ⁴⁸Ca with the CANDLES III system, which consists of CaF₂(pure) scintillators. Rejection analyses for background events from radioactive contaminations in the CaF₂(pure) scintillators were effective to reduce backgrounds in Q_ββ -value region. As the results, no events were observed in the region for the data of 131 days × 86 kg. It gave a lower limit 6.2 × 10²² year (90 % C.L.) for the half-life of 0νββ of ⁴⁸Ca. For higher sensitive measurement of ⁴⁸Ca 0νββ, we have developed new techniques for ⁴⁸Ca enrichment and CaF₂ scintillating bolometer. In this paper, we will also show current status of these techniques.