A. Iltis | Searcharxiv

arXiv2026

Preventing quart-NaI adhesion in Bridgman growth using ammonium iodide

Adhesion between NaI(Tl) single crystals and the walls of quartz ampoules remains a major limitation for Bridgman growth under sealed conditions, particularly for applications requiring ultra-radiopure scintillators for dark matter searches, where sealed handling is essential. In this study, ammonium iodide (NH4I) was used as an additive to generate HI in situ, thereby suppressing the NaOH-SiO2 reaction that forms adhesive sodium silicate phases. Small-diameter crystals (8 mm) were first grown to determine the NH4I concentration required to eliminate adhesion. The optimized condition was then applied to the growth of a large NaI(Tl) crystal. A crack-free and bubble-free NaI(Tl) crystal with dimensions of 3 inches in diameter by 3 inches in length was successfully grown. The crystal exhibited a light output of 59,000 photons/MeV, which is higher than that of the commercial NaI(Tl) crystals used as references in this study.

physics.ins-det↗

arXiv2020

Development of ultra-pure NaI(Tl) detectors for the COSINE-200 experiment

The annual modulation signal observed by the DAMA experiment is a long-standing question in the community of dark matter direct detection. This necessitates an independent verification of its existence using the same detection technique. The COSINE-100 experiment has been operating with 106~kg of low-background NaI(Tl) detectors providing interesting checks on the DAMA signal. However, due to higher backgrounds in the NaI(Tl) crystals used in COSINE-100 relative to those used for DAMA, it was difficult to reach final conclusions. Since the start of COSINE-100 data taking in 2016, we also have initiated a program to develop ultra-pure NaI(Tl) crystals for COSINE-200, the next phase of the experiment. The program includes efforts of raw powder purification, ultra-pure NaI(Tl) crystal growth, and detector assembly techniques. After extensive research and development of NaI(Tl) crystal growth, we have successfully grown a few small-size (0.61$-$0.78 kg) thallium-doped crystals with high radio-purity. A high light yield has been achieved by improvements of our detector assembly technique. Here we report the ultra-pure NaI(Tl) detector developments at the Institute for Basic Science, Korea. The technique developed here will be applied to the production of NaI(Tl) detectors for the COSINE-200 experiment.

physics.ins-det↗