We report a study on the background of the Advanced Molybdenum-Based Rare process Experiment (AMoRE), a search for neutrinoless double beta decay (0νββ) of 100Mo. The pilot stage of the experiment ...was conducted using ∼1.9 kg of 48deplCa100MoO4 crystals at the Yangyang Underground Laboratory, South Korea, from 2015 to 2018. We compared the measured β/γ energy spectra in three experimental configurations with the results of Monte Carlo simulations and identified the background sources in each configuration. We replaced several detector components and enhanced the neutron shielding to lower the background level between configurations. A limit on the half-life of 0νββ decay of 100Mo was found at T1/20ν≥3.0×1023 years at 90% confidence level, based on the measured background and its modeling. Further reduction of the background rate in the AMoRE-I and AMoRE-II are discussed.
The AMoRE-II experiment will search for the 0 νββ decay of 100 Mo nuclei using molybdate crystal scintillators, operating at milli-Kelvin (mK) temperatures, with a total of 80 kg of 100 Mo. The ...background goal for the experiment is 10 –4 counts/keV/kg/year in the region of interest around the 0 νββ decay Q-value of 3,034 keV. To achieve this level, the rate of background signals arising from emissions produced by decays of radioactive impurities in the detector and shielding materials must be strictly controlled. To do this, concentrations of such impurities are measured and are controlled through materials selection and purification. In this paper, we describe the design and the construction materials used to build the AMoRE-II detector and shielding system, including active and passive shielding, the cryostat, and the detector holders and instrumentation, and we report on measurements of radioactive impurities within candidate and selected materials.
The formation of carbonaceous particles from the hydrogen-free precursors CCl
4 and C
3O
2, both diluted in argon was studied behind reflected shock waves in the temperature range 1400 K ≤ T ≤3700 K ...and at pressures 1.3 bar ≤
p ≤ 4.5 bar. The appearance of particles was measured by laser light extinction (LLE) and by laser induced incandescence (LII). Also, some time and spectrally resolved emission measurements were performed. The LLE experiments are sensitive to the optical density of the post-shock gas-particle mixture and show a time-dependent increase, depending on the detailed reaction conditions. The evaluation of the experiments at a reaction time of t = 1 ms results in a double, bell-shaped temperature dependency of the optical density. The LII-experiments, which are sensitive to the particle size, provide particle growth curves determined from several “identical” shock tube experiments with delayed triggering of the LII heat-up laser. Particle sizing experiments at a reaction time of t = 1 ms after shock-induced heat-up of the initial gas mixtures also clearly yield a double, bell-shaped temperature dependency of the particle diameter and confirm the optical density experiments. The shock tube was also equipped with a molecular beam system allowing supersonic beam probing from the shock-heated gases. Particles were collected on TEM grids and visualized by HR-TEM. The sizes of these images more or less confirm the LII sizing.
