Provided are a thallium bromide semiconductor radiation detector having stable measurement performance with little noise increase even during prolonged measurement, and a nuclear medicine diagnosis device employing the same. In a semiconductor radiation detector using thallium bromide as a semiconductor crystal sandwiched between cathode and anode electrodes, a remaining surface, among surfaces of the semiconductor crystal, which is other than a surface covered with the cathode or anode electrode, is covered with a passivation layer including any one of two materials, that is, fluoride of thallium and chloride of thallium, or a mixture of any one of the two materials and bromide of thallium.
