Our research group at Nagoya University pursues a programme of radiation detector development for a range of applications. The purpose of this experiment is to evaluate the defects in TlBr single crystals, which are used for semiconductor radiation detectors. TlBr has recently been developed as an alternative to the high purity germanium (HPGe) detector. It can be operated at room temperature and shows excellent energy resolution of less than 1%. The current key issue is how to improve the yield rate of detector production. It is imperative to understand the whole fabrication process so that yield rate of production can be improved. In this experiment, the level of crystal defects in TlBr crystals will be evaluated by neutron Bragg-dip imaging, above all, to understand the relation between crystal quality and detector performance.