On-line system for measurements of nuclear level lifetimes

The on-line system for multidimensional measurements of delayed coincidences is described. It made it possible to use the compensation technique for the amplitude dependence of the time distribution of coincided pulses while detecting γ radiation within the energy range of 50-100 keV. The system consists of: two scintillation detectors with NaI(Tl) crystals, pulse shapers, a coincidence circuit, data recording and computer communication units. The analysis of the results obtained shows that the compensation of time shifts permits to improve dramatically the time resolution and the shape of time distributions, and also to decrease the gravity centre spread in the case of wide- and low-energy amplitude windows. The above system has been used for lifetime measurements of nuclear energy levels by the comparison of time distributions of delayed and instant coincidences. The obtained values of halflives of the excited states of 147Sm and 153Eu agree well with available data. The method described has an opportunity to increase the accuracy and reliability of lifetime measurements, the lifetimes being considerably smaller than the time resolution of the system