Patent ID: 7342997

Claim:
A method for measuring a dead time of a pulse type X-ray detector comprising: adopting a first condition and a second condition, each of the two conditions having a feature that the condition has plural setting states which can be changed with one another so that a state of an X-ray path from an X-ray source to the X-ray detector can be altered so as to vary an intensity of an X-ray received in the X-ray detector; adopting at least three setting states for the first condition; adopting a first setting state and a second setting state for the second condition so that: the received X-ray intensity in the first setting state is different from the received X-ray intensity in the second setting state, and a ratio of the received X-ray intensity in the second setting state to the received X-ray intensity in the first setting state is constant in each of the at least three setting states of the first condition; setting the first setting state for the second condition; carrying out a first observation in which the X-ray is emitted from the X-ray source and travels through the X-ray path and then is received in the X-ray detector so that an output of the X-ray detector is observed as a first observed X-ray intensity for each of the at least three setting states of the first condition; changing the first setting state to the second setting state for the second condition; carrying out a second observation in which the X-ray is emitted from the X-ray source and travels through the X-ray path and then is received in the X-ray detector so that an output of the X-ray detector is observed as a second observed X-ray intensity for each of the at least three setting states of the first condition; determining the ratio and the dead time in a manner that: there is made up a relational expression defining a relationship among the first observed X-ray intensity, the second observed X-ray intensity, the ratio and the dead time for each of the at least three setting states of the first condition, and the ratio and the dead time are determined so that the relational expressions are most satisfied in total provided that the first observed X-ray intensity and the second observed X-ray intensity are handled as known while the ratio and the dead time are handled as unknown; and storing the determined dead time in a storage device.