A 252Cf fission-product source and the INL on-line isotope separator were used to supply isotope-separated fission-product nuclides to a total absorption -ray spectrometer. This spectrometer consisted of a large (25.4-cm diameter x 30.5-cm long) NaI(Tl) detector with a 20.3-cm deep axial well in which is placed a 300-mm2 x 1.0-mm Si detector. The spectra from the NaI(Tl) detector are collected both in the singles mode and in coincidence with the events detected in the Si detector. Ideally, this detector would sum all the energy of the rays in each cascade following the population of daughter level by decay, so that the event could be directly associated with a particular daughter level. However, there are losses of energy from attenuation of therays before they reach the detector, transmission of rays through the detector, escape of secondary photons from Compton scattering, escape of rays through the detector well, internal conversion, etc., and the measured spectra are thus more complicated than the ideal case and the analysis is more complex. Analysis methods have been developed to simulate all of these processes and thus provide a direct measure of the intensity distribution as a function of the excitation energy in the daughter nucleus. These data yield more accurate information on the distribution than conventional decay-scheme studies for complex decay schemes with large decay energies, because in the latter there are generally many unobserved and observed but unplaced rays.
The TAGS data have been analyzed and published [R. E. Greenwood et al., Nucl Instr. and metho. A390(1997)] for 40 fission product-nuclides to determine the intensity distributions.
148Pr (2.0 min),
148Pr (2.27 min),
152Nd-152Pm (4.1 min),
154Pm (1.7 min),
- David Nigg, (208) 526-7627, Send E-mail