Thallium bromide (TlBr) has been one of the promising gamma-ray detector materials because of its high gamma-ray attenuation length, availability of room-temperature operation, and relatively high energy resolution. However, the high-resolution detector has been limited to a relatively small size. Hence, the next task in the TlBr development is to establish fabrication processes of large detectors. As one of the candidates for evaluating the TlBr crystal quality, we demonstrated neutron Bragg-dip imaging, which is one of the neutron diffraction techniques and is based on wavelength-resolved neutron imaging. All the studied samples seemed to be imperfect crystals and slightly distorted. Although differences in crystal orientation distributions among the samples cannot be obtained from the present data, it is suggested that one of the crystals has a boundary, or possibly a small crystal grain near the crystal center, which may result in a low-quality electron mobility and lifetime (μτ) product.

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