This invention provides a radiation detector using a scintillator having both a strong luminescence intensity and a short time constant. The 3-D UCT system includes an imaging chamber having a plurality of piezoelectric elements. In the second arithmetic pipeline, the critical stage of the first arithmetic pipeline is divided to multiple stages. The slave device accepts the clock signal, and uses it as a clock signal to drive functions of the slave device. Consequently, the light-emitting device has excellent color gamut.