Fission yields and recoil ranges determined by a Ge(Li) detector

The excellent resolution of gamma rays by Ge(Li) detectors is used to determine 239Pu fission yields and recoil ranges of fission products from 233U and 239Pu. A combination of a 2-cm3 Ge(Li) detector and a low-noise, room-temperature FET pre-amplifier combination giving a FWHM of 3.6 keV for 122 keV gamma-ray was employed. Irradiation and cooling times were optimized in order to obtain best resolution for different fission products. The purity of each photopeak used was ascertained by following the decay and determining the half-life. As part of a program on determining fission yields of several heavy-element nuclei, fission yields of 239Pu were determined by this technique. Thin, electroplated targets of 239Pu and 235U were simultaneously irradiated with neutrons and the recoiling fission fragments were collected in superpure aluminium foils. From an analysis of the gamma-ray spectra of fission products in the catcher foils, the yields of various nuclides in the thermal-neutron-induced fission of 239Pu were determined relative to that of 235U. These yields were compared with available radiochemical values. Recoil ranges of fission products from 233U and 239Pu in aluminium were also determined gamma-spectrometrically and compared with radiochemical values. This method affords determination of fission yields with an accuracy of 2-5% and ranges with an accuracy of 1-2%. (author)