The141Eu nuclide and its decay properties

Abstract

The nuclide 141Eu is identified to have two beta decaying isomers, ~41gEu and ~4~mEu, whose decay half-lives are measured to be 40.0_+0.7s and 3.3_+0.3s, respectively. Their decay properties are studied by means of beta and gamma spectroscopy techniques. The states with J~ assignments in *4~Sm thus deduced are compared with those of the other odd-A, N=79 isotones. The total decay energy of ~gEu is measured to be 6.03_+0.10 MeV, which is compared with the predictions of several mass formulae and with the decay energy systematics of the N=78 isotones. The a41gEu and ~4~mEu are deduced to have J~= 5/2 + and 11/2 , respectively. A 96.4 keV isomeric transition between them is found to be an E3 transition with a B(E3)=l.6+_O.4e2fm 6. The structure of 141Eu is compared with that of the other N = 78 isotones.

Decay properties of139mSm and139Eu

“…The 139Eu nuclide was first identified by Westgaard et al [3] and they found it to decay with a half-life of 22__ 3 s. Subsequently, van Klinken and Feenstra [4] reported that its decay populates primarily the 11/2-, 457.4keV isomeric state of 139Sm (139mSm) and they thus assigned a J~= 11/2-to the ground state of 139Eu. However, nuclear systematics indicate that the decay properties of 139Eu should resemble those of 11/2-141mEu, which we studied previously [5]. This implies that the decay of 139Eu would also populate several other relatively high spin states in 1398m and this has been borne out in the present work.…”

“…At this energy the interferring activities unavoidably produced were exactly those we encountered in our study of the decay properties of ~39gSm [2]. Almost all of these unwanted activities came from the decay of 142m'gEU [8], 141m'gEu [5], 141m'gSm [9], 14~ [10], 1398m [2], ~38Pm [1] and 137pm [11]. The decay properties of these nuclides are well known from the references cited.…”

New exotic neutron-deficient nuclei nearN=82

“…The assignment of the spin 11/2-for the 22s lelGd is tentative. This scheme is likely based on the 3.3s isomeric state of 14~Eu located at 96.5 keV [23]. As a matter of fact, a 96.5 keV transition is weakly observed in the single He-jet spectra with a half-life roughly estimated to be of the order of 10s which could consist in a mixing of 22s and 3.3s activities due to a simultaneous production of 14~Gd and 141mgu.…”

States inN=79142Eu populated in the decay of142Gd

“…The data acquisition was started 20 s after the bombardment in order to allow shorter-lived activities to decay substantially. Several well known contaminating activities were also inevitably produced, either directly or as daughter activities, at this bombardment energy: 145 g, mGd [22,23], 144Gd [24], a43 g, mGd [25,26], 143Eu [2], a42g'mEu [3], 14lg'mEu [8], 141g'mSm [7,27], 14~ [13,28], 139g'mSm [11,12] la9 Pm [9] and 138Pm [10]. Several lines from the decay of ~42Gd that were clearly observed in the X-y coincidences were thus strongly contaminated in the y-ray singles spectrum.…”