A study of the prompt gamma rays of 252Cf-fission

The prompt gamma-ray spectra in the range between 50 and 550 keV were measured simultaneously at angles of 90 deg and 180 deg with respect to the fragment direction. By using fission fragment energy as an additional parameter, it was possible to find well-resolved gamma lines; cases of Doppler shifts were easily observed. The amount of shift was used to deduce fragment masses. The type of Doppler spectrum was used to classify gamma life-times according to three intervals: (t < 10-12s, 10-12s < t < 2 x 10-9s, 2 x 10-9s < t < 10-7s). The first limit is due to the fragment stopping time in the backing of the Cf-foil (10-12s). The fragment time of flight from source to detector determined the second interval to 10-12 < t < 2 x 10-9s, while the last interval was limited by the electronic coincidence width to 10-7s. About half of the gamma lines were found to lie in the second interval and could, therefore, be assigned to definite fragment masses. (author)