Scintillation properties of and proton-induced effect on CdWO₄ crystals

The scintillation properties of CdWO₄ (CWO) crystals have been studied to develop an X-ray scanner for a cargo container. The CWO crystal is composed of higher effective-Z-number materials, and it has a high density, therefore, a high detection efficiency for X-rays and γ-rays is expected. We selected various CWO crystals made in Russia (Novosibirsk) and China for comparison. The X-ray luminescence and the scintillation properties were studied with various sizes (4 × 4 × 30 mm³, 4 × 7 × 30 mm³ and 4 × 12 × 30 mm³) for polished and unpolished crystals. The transmittance of the CWO crystals was found to be 75% in the visible range. The X-ray emission spectrum of CWO crystals showed a peak at 480 nm. The scintillation properties, like the decay time, the energy resolution and the light yield, were measured and compared by using gamma source excitation. All samples exhibited similar decay times, with a value of 12 μs. The light yield and the energy resolution of the Russian samples were found to be significantly better than those of the Chinese samples. The proton response and radiation hardness of the CWO crystal were studied by using the 45-MeV proton beam from the MC-50 cyclotron at the KIRAMS (Korea Institute of Radiological and Medical Science).