Speaker
Description
To calculate reliably and accurately concentrations and activities for nuclides generated or depleted by neutron reactions and radioactive decays in nuclear fuel, it is necessary to use the updated nuclear decay data such as half-lives, branching ratios, and $\gamma$-ray spectra. The Evaluated Nuclear Structure Data File (ENSDF) contains required decay data for all nuclides, which is periodically revised by evaluating all available experimental data. However, the latest revision of ENSDF was more than 10 years ago for many nuclides, and the evaluated data for them are old. Therefore, we are performing new evaluations of decay data for these nuclides. A few examples of our evaluations were reported in the last year’s symposium. This presentation gives our evaluations performed in this year.
An example is the -decay half-life of 120gI. We carefully read all of the references regarding the measurements of this half-life, and accumulated reliable data from them. The statistical analyses of these data were made, and the recommended value has been determined to be 81.8 (2) min. Similar procedures were taken to determine the recommended values of the half-lives of 120gCs and 120gXe to be 64 (3) s and 46 (6) min, respectively. Another example is the excitation energy of the metastable state 120mI. We adopted the excitation energy from a recent reference of the sensitive $\gamma$-ray measurement.
JENDL-5 Decay Data File (DDF) is one of the sub-libraries of JENDL-5 and was publicized in 2021. Most of the data in JENDL-5 DDF were taken from ENSDF. In case of the A=120, the latest revision of ENSDF was made in 2014. We verified the values in JENDL-5 DDF by using our newly evaluated values. For example, the half-lives of 120gI, 120gCs and 120gXe in JENDL-5 DDF were taken from old references, and have been changed to the new values as mentioned above. Also, the excitation energy of 120mI in JENDL-5 DDF has been revised by the present evaluation. The old value had large uncertainty because it was adopted from a reference of low-resolution-ray spectra measurements.
