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.