The intrinsic quadrupole moment of 176Lu has been determined by Coulomb excitation with a-particles to be 6.98 • 0.I0 b. Evidence for a new level at approximately 578 keV with presumably collective structure is presented.

The intrinsic quadrupole moment of 17~Lu has been determined by Coulomb excitation with s-particles to be 6.98 • 0.i0 b. Evidence for a new level at approximately 578 keV with presumably collective structure is presented.The electromagnetic properties of 176Lu are of much current interest since it has been proposed to use the B-decay of its K,I ~ = 7,7-ground state to ZT~Hf (T1/2 = 3.6x10 I~ y) as a cosmic chronometer for s-process nucleosynthesis (see e.g. [i] and references cited therein). The ground-state decay, however, is complicated by the K,I ~ = 0,i-isomeric state at 127 keV which decays to 17~Hf with a half life of only 3.68 hr. If, at stellar temperatures, this short-lived isomer is linked to the ground state by electromagnetic interaction, then the total half life against g-decay will be considerably smaller than the known ground-state value and the applicability of 176Lu as cosmic clock may become questionable. In order to make estimates possible to what extent the isomer can be excited, we have initiated a general study of the electromagnetic properties of 17~Lu, part of which is the precise determination of its intrinsic quadrupole moment reported in this communication.The experiment was performed by exposing thin (<10 pg/cm2), isotopically pure 17~Lu targets to s-particle beams with energies of 9.5, 13.5 and 14.0 MeV obtained from the University of Frankfurt Van de Graaff accelerator. The targets were fabricated using the Karlsruhe isotope separator. Elastically and inelastically scattered 1 This ShortNote has already appeared in Vol. 309 No. 3 (1983) pp. 275-276 but unfortunately the list of authors was not complete s-projectiles were detected by two cooled and collimated Si surface-barrier detectors positioned at • o with respect to the beam direction. An energy resolution of typically 22 keV (FWHM) was achieved. At the beam energy of 13.5 MeV two separate measurements were performed and, hence, a total of 8 spectra was obtained. A representative spectrum measured at 13.5 MeV is shown in Fig. I. This spectrum shows excitation of the ground band up to and including the 10-state, with an additional peak seen at 578 keV (marked by "?"). This latter group is probably due to a collective 176Lu level which is reported here for the first time. Since the intensity of this peak strongly decreases with decreasing projectile energy and, moreover, its position in the spectrum is independent of the projectile energy, it is most unlikely that this peak is caused by a target contaminant.The excitation cross section of the 8-state was obtained relative to the elastic-scattering strength by using a computer code that separated the 8-and 7-peaks in an iterative, selfconsistent procedure assuming identical line shapes. The intensities of the other groups were obtained by fitting third-order polynomials to the background below and above each peak.To deduce the intrinsic quadrupole moment from the measured excitation probabilities, semiclassical Coulomb-excitation cross sections were calculated using the...

No abstract

No abstract

No abstract