Nuclear Structure and Decay Data for A=149 Isobars

Abstract

Experimental nuclear structure and decay data are evaluated for all the 17 known nuclides of mass 149 (Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb). Detailed compiled and evaluated spectroscopic information is presented for each reaction and decay dataset, and recommended values are provided for level properties, α, β and γ radiations, and other spectroscopic parameters, based on an evaluation of all the available experimental data for A=149 isobaric nuclides. Although large amounts of nuclear spectroscopic data are available for nuclides of A=149, yet large gaps in knowledge exist, as described below. For the lowest atomic number nuclide 149Xe, only the isotopic identification has been made, with no data for its ground-state half-life. For 149Cs, 149Tm and 149Yb information is available for only the respective ground states. For 149Ba, 149La and 149Er, limited data exist for excited states. Many of the decay schemes of radioactive nuclei of A=149 are considered as incomplete, either due to large energy differences between the highest observed excited states in daughter nuclides and the respective Q-values, or due to the lack of confirmed γ-ray data, as listed below: 149Cs → 149Ba, 149Ba → 149La, 149La → 149Ce, 149Ce → 149Pr, 149Pr → 149Nd, 149Tb(4.17 min) → 149Gd, 149Ho(21.0 s and 56 s) → 149Dy, 149Er(4 s and 9.6 s) → 149Ho, and 149Tm → 149Er. No data exist for the decay of 149Yb to 149Tm. Data for half-lives of the excited states in this mass chain are generally lacking as given below by the number of excited levels of known half-life / approximate number of known levels in a nuclide: 2/17 for 149Ba, 0/18 for 149La, 3/53 for 149Ce, 3/44 for 149Pr, 17/110 for 149Nd, 9/90 for 149Pm, 10/210 for 149Sm, 2/125 for 149Eu, 6/270 for 149Gd, 5/200 for 149Tb, 3/80 for 149Dy, 3/90 for 149Ho, and 3/14 for 149Er. This work supersedes earlier evaluations of A=149 nuclides published by 2004Si16, 1994Si18, 1985Sz01 and 1976Ho17.