Quantitative evaluation of the intrinsic X-ray peak probability of a superconducting tunnel junction with the cascade process model of primary photoelectrons

The electron collision cascade process of primary photoelectrons generated by absorbed X-rays was studied to develop a clear model of the signal producing process of a superconducting tunnel junction (STJ), and the intrinsic peak probability P(1) of the STJ was calculated as a function of X-ray energy. X-rays of 5-18 keV were measured by a 178 mu m x 178 mu m Nb/Al-AlO(2)/Al/Nb STJ with the Nb electrode thickness of 200 nm and P(1) was experimentally obtained. The calculated P(1) agreed well with the measured one for the range of X-ray energies of 5-12 keV. The numerical evaluation of P(1) with this model reveals that the increases of the electrode thickness is effective to increase P(1).