Center for Underground Physics

Low Temperature

Low Temperature R & D

Low temperature sensors have opened up great opportunities by enabling measure-ments of tiny energy depositions from particle interactions. Because of their excellent sensitivity, such sensors have played important roles in rare phenomena searches such as direct dark matter searches and neutrinoless double beta decay experiments. The low temperature group at CUP has developed the AMoRE crystal detectors which use the MMC (Metallic Magnetic Calorimeter) technique to measure phonons and scintillation photons produced by the particle interactions in the crystal. We conduct R&D to improve the performance of the phonon and photon detection using various low temperature techniques. We have tested various Mo-based crystals for the future double beta decay experiment. We are also working on a low temperature facility to accommodate a large detector array and shield structure for the large-scale experiment.

Purification

Why do we need purification?

Searching for the rare events like the neutrinoless double beta decay and the dark matter interactions for the proposed experiments requires to use developed detectors made from initial materials with extremally low internal radioactive background. So, purification of materials used for the detectors is one of important direction for R&D program of CUP.

How do we purify?

We use various purification techniques for reduction of radioactive contamination in 100MoO3 powder, as a main initial material for the AMoRE detector, and in NaI powder, as a main initial material for the COSINE detector.

For purification of molybdenum tri-oxide, we apply combination of sublimation with wet chemistry techniques using home-made sublimation and annealing machines for producing of final product:

For purification of sodium iodide, we have designed developed mass-scale purification facility based on the fractional recrystallization from water:

How do we check purity of our products?

We use Inductively Coupled Plasma Mass Spectrometer Agilent 7900 for trace level analysis of our materials and products. The use of ICP-MS method conducted with UHMI and He modes provides high precise and accurate measurement of many elements, like Th, U, Ba, Sr, Pb, K, etc. on a ppt level.

Simulation

Why we are doing computer simulation?

The center for underground physics aims to reach the most sensitive parameter spaces for searches on a dark matter and neutrinoless double beta decays, which are extremely rare event experiments requiring ultra-low background rates. In order to meet the experimental requirements, we must understand background sources from detector components, surrounding materials of the detector, and cosmic muons.

To save time and to optimize design of each experiment for increasing signal as well as reducing backgrounds, we are performing simulations of various backgrounds in the experiments, which would provide us improving a sensitivity of our experiments.

What do we simulate?

Geant4 (GEometry ANd Tracking) is one of useful tools for simulations of our experiments. Current we are doing the KIMS-NaI detector for a search on dark matter and AMoRE detector for a search on neutrinoless double beta decays simulations to design the experiments using Linux computer cluster (see Fig. 1 and 2). These simulations give us cost and time savings for the experiment, more importantly improving sensitivity of each experiment.

• Figure 1 :

  KIMS detector simulation

• Figure 2 :

  AMoRE detector simulation.