Alpha decay of neutron-deficient rhenium and osmium isotopes

Abstract

Neutron-deficient osmium and rhenium isotopes were produced by bombarding an enriched 144Sm target with beams of 27A1 and 2sSi. Previously reported decay data concerning ~6s'~69'~7~ were confirmed. Three new e groups, observed in the ~44Sm +27A1 reaction, were assigned to the decay of 166't67'~68Re based on excitation functions, e-energy systematics and theoretical half-life predictions. Their decay properties are: It is proposed that two e groups, observed in the 144Sm+2SSi reaction, originate from isomeric states in 168,169Re" Our measured data for the isomeric states are: 16StoRe, E~ = 5,250 (10) keV, T1/2 = 6.6 (15) s and 169raRe, E, = 5,050 (10) keV, T1/z=12.9(ll)s.

Revision of the decay data of166?170Re, including new isomers167m,169mRe

“…We can, however, not rule out that the 5.50 MeV e-rays belong to 16~Re, as it was reported in [10]. The earlier reported 5.26 MeV [8,9] and also the new 5.02 MeV e-rays display a similar excitation function as 167W and are consequently assigned to 167Re (Fig. 4).…”

“…The production ratio of 5.26 MeV e-rays and 363 keV v-rays, however, increases rapidly for higher irradiation energies. This excludes an assignment of the 5.26 MeV e-radiation to 168Re [8,9]. The trend of the production ratio is similar to that of 94keV or ll0keV v-rays, both belonging to t'6vW [4].…”

“…A 5.506 MeV e-ray had earlier been attributed to 165Re El0], but was reassigned to 166Re by other authors Ell,12]. The earlier reported e-line of 5.372MeV of ~6VRe Ell, 12] and of 5.136MeV of 16SRe [12] were later ascribed to 166Re, and 167Re, respectively [9]. A further complication arises from the fact that the tungsten isotopes 163-~65 W are known to have similar e-ray energies of 5.384, 5.148, and 4:902 MeV [13,14] and half-lives being close to those reported for the rhenium isotopes.…”

“…By means of the so far known e-ray energy systematic, Schrewe et al [9] claimed that these e-rays had a proper mass assignment, but belonged to the decays of two isomers, 168~Re and a69mRe. For 168gRe, they added a new 4.894 MeV e-ray [9]. In the case of the lighter isotopes 165-~67Re ' disagreeing e-decay data are found in the literature.…”

“…4). A new mass assignment of the 5.26 MeV e-ray, which had earlier been attributed to 168Re [-8] or t68mRe [9], is then obtained. In order to avoid experimental shifts in the excitation function data due to jet-transport efficiency or beam current measurement, we have compared in Fig.…”