The Life-time Measurements of Some High-spin States in the ^138,139Ce and ^141,142Nd Nuclei

Abstract

A search for high-spin isomeric states in the 138,139Ce anc 141,142Nd nuclei has been made using (α, xn) reactions and the intrinsic pulsing of the 225-cm Stockholm cyclotron. In 138Ce, besides the known 7- isomeric state at 2 128.8 keV, another one at 3 538.5 keV, 10+, with T 1/2 = (78 ± 5) ns has been found. In 139Ce a new isomeric state at 2 631.5 keV, 19/2-, with T 1/2 = (70 ± 5) ns has been identified. Also in 141Nd a high-spin isomeric level exists probably at 3 104.9 keV with T 1/2 = (26 ± 5) ns. In 142Nd the level at 3 453.0 keV, with spin I = 6, shows a half-life T 1/2 = (1.3 ± 0.1) ns while that at 4 718.5 keV, I = 8, decays with a half-life of about 0.8 ns. The time distributions in 142Nd show that the 3 242.9 keV, I = 7, or the 3 456.2 keV, I = 8, level is also delayed and decays with T 1/2 = (1.6 ± 0.1) ns. The deduced transition probabilities are compared to theoretical predictions.

Energy levels in141Nd from fusion evaporation study

“…A total of 48 transitions have been placed in the proposed level scheme shown in figure 1. In the rest of the paper, unless otherwise mentioned, earlier experimental work refers to the the earlier work by Ludiejevosky et al [10,11]. Almost all gamma rays reported in the earlier work have been observed in this experiment.…”

“…The nucleus 141 Nd was studied earlier using the reactions 140 Ce(α, 3nγ ) [10] and 140 Ce(α, 5nγ ) [11]. States up to about 3 MeV in excitation energy and 17/2h in spin are known from the above experiments.…”

Electromagnetic transition rates in theN=80nucleus58138Ce

“…Since the exact value for the mixing ratio is unknown for this transition, the reduced transition probabilities assuming the limiting values of either pure M 1 or pure E2 have been calculated. A previous study [33] [19] the 338 keV transition was assigned to have pure M 1 character. A half-life of T 1/2 = 80(9) ps was obtained for the I π = 14 + state using the centroid shift method in the current work (see figure 4).…”