VCI2019 - The 15th Vienna Conference on Instrumentation Contribution ID: 674 Type: Poster

High light yield calcium iodide (CaI2) scintillator for astroparticle physics

Large light yield of scintillator can be a key to develop a good detector for astroprticle physics. Calcium Iodide (CaI2) crystal is discovered by Hoftadter et al. in 1960s and known to have large light yield. Universityof Tsukuba and IMR, Tohoku University are jointly developing CaI2 crystal from 2016 using updated facilities and leading-edge techniques. At first, vaporization of CaI2 material was problem because of its close melting point and boiling point. We overcame this problem by sealing off a quartz tube to prevent evaporation and finally we succeeded to grew 1 inch CaI2 crystal by Bridgman method. Small piece of CaI2 crystal was sliced off and polished in a dry room whose humidity is less than 1 %. Energy response of CaI2 coupled with photomultiplier tubes was measured using 137Cs gamma-ray source. Photoelectric peak of 662 keV gamma-ray of CaI2 was 2.7 times higher than that of NaI(Tl) and light yield of CaI2 was estimated to be 107,000 ph./MeV. While CaI2 showed good scintillation property, it also showed very strong cleavability and deliquescent. Since these characteristics makes it difficult to cut and polish CaI2 crystal, we tried to grow CaBr2-xIx crystal by replacing iodine (I) with bromine (Br) to reduce cleavability. We found larger bromine fraction gives smaller cleavability and smaller light yield. A crystal with 2 % europium (Eu) and quarter bromine (Eu2%: Br0.5I1.5) gave 95,400 ph./MeV. We plan to optimize fraction of Eu and Br next.

Primary authors: Dr IIDA, Takashi (University of Tsukuba); Dr KAMADA, Kei (Tohoku University); Dr YOSHINO, Masao (Tohoku University) Presenter: Dr YOSHINO, Masao (Tohoku University) Session Classification: Poster Session A

Track Classification: Astroparticle Detectors