Application of the gross theory to FP decay heat calculations in the new light of TAGS measurements

On the basis of the recent knowledge that the decay data measured by Total Absorption Gamma-ray Spectrometer (TAGS) is free from the so-called pandemonium, the prediction power of the gross theory of beta-decay was studied. By comparing the theoretical prediction with the INEL/TAGS data, we conclude that the gross theory predicts well the total energy release, or Eβ + Eγ .H owever, whenEβ and Eγ are dealt with separately, the prediction power of the theory has a limitation. This is one of the reasons why we need further TAGS measurements. In the early stage of development of the fission product (FP) decay data libraries around 1980, a serious inconsistency between calculations based on these libraries and sample- irradiation measurements was experienced in Japan, in the US and also in Europe. This problem was practically circum- vented by introduction of nuclear model calculations (1) in the cases of the JENDL FP Decay Data File and ENDF-B/VI. This type of inconsistency between summation calculations and the experiments was proved to be originated from so-called pandemonium problem (2). Recently it was shown that the use of the experimental results based on the total absorption gamma-ray spectrometer (TAGS) improve the situation fairly well without introducing any theoretical prediction (3). TAGS measurement of 45 FP nuclides had been conducted in the US in 1990's (4). Reacent years a European group started a new series of TAGS measurement (5). This new activity is being conducted in close contact with the International Nuclear Data Evaluation Working Party of OECD/NEA. In this paper, the US TAGS results were analyzed on the basis of the gross theory of beta decay in order to improve the prediction ability of the theory.