Program - Brookhaven National Laboratory

f 81 (2002) 1. [3] R.G. Helmer et al., Nucl. Instrum. Methods Phys. Res. A 511 (2003) 360. [4] N. Nica
et al. Phys. Rev. C: 70 2004 054305; 77 2008 034306; 80 2009 064314.
HD 5 5:00 PM
Search for Fission Decays of High-K Isomers in 254 Rf ∗
J. Chen, F. G. Kondev, D. Seweryniak, M. P. Carpenter, M. Albers, M. Alcorta, P. F. Bertone, J. P.
Greene, C.R. Hoffman, R.V.F. Janssens, T.L. Khoo, T. Lauritsen, C. Nair, A.M. Rogers, G. Savard, S.
Zhu, Argonne National Laboratory, Argonne, IL 60439, U.S.A.. H. David, D. Doherty, University of
Edinburgh. P. Greenlees, J. Konki, S. Stolze, University of Jyvaskyla. K. Hauschild, CSNSM, Orsay. D.
J. Hartley, U.S. Naval Academy. S.S. Hota, Y. Qiu, University of Massachusetts Lowell. C. J. Chiara,
University of Maryland and Argonne National Laboratory.
Nuclei in the transfermium region near the Z = 100 and N = 152 subshell gaps are predicted to be well
deformed with an axially-symmetric shape. Their single-particle spectra are dominated by high-K orbitals
near both the proton and neutron Fermi surfaces. These conditions favor the presence of high-K, multiquasiparticle
states at relatively low excitation energies, some of which can be expected to be long-lived due
to the conservation of the K quantum number. Two-quasiparticle K π =8 − isomers are observed in several
even-even N=150 isotones, from 244 Pu (Z = 94) to 252 No (Z = 102), and those have been associated with
the two-quasineutron ν 2 (7/2 + [624], 9/2 − [734]) configuration. In the heavier Rf (Z = 104) isotopes, the
proton Fermi level is located between the π7/2 − [514] and π9/2 + [624] orbitals, and hence, one may expect
a two-quasiproton K π =8 − state at low excitation energy. Multi-quasiparticle blocking calculations predict
that in 254 Rf (N = 150) the two-quasineutron and two-quasiproton, K π =8 − configurations compete for
favored yrast status, with the one lowest in energy expected to be a long-lived K-isomer. In addition,
calculations predict a particularly favored K π =16 + four-quasiparticle state at 1.95 MeV formed by the
coupling of the two K π =8 − configurations. This is a candidate for an even longer-lived state in 254 Rf, which
is analogous to the K π =16 + (T 1/2=31 y) isomer in the rare-earth nucleus 178 Hf. Since the 254 Rf ground
state disintegrates by spontaneous fission with a relatively short lifetime (T 1/2=23 (3) µs), identification
of these high-K states is particularly worthwhile, as they can provide direct evidence for the role that
K-isomers may play in the enhanced stability of super-heavy nuclei. We have carried out a search for the
predicted two- and four-quasiparticle states in 254 Rf using the 50 Ti + 206 Pb heavy-ion fusion-evaporation
reaction and the Argonne Fragment Mass Analyzer (FMA). A 242.5 MeV 50 Ti beam with an intensity of
∼200 pnA was provided by the ATLAS accelerator. The recoiling reaction products were transported to
and separated by the FMA, identified by their m/q ratio using a Parallel Grid Avalanche Counter detector
and implanted into a 160-by-160-strip Double-sided Silicon Strip Detector (DSSD) at the FMA focal plane.
Spatial and time correlations between implanted nuclei and their subsequent fission decays were detected
within a single DSSD pixel. Analysis of such events allowed characterization of the decaying state. The
data from this experiment will be presented and the results will be discussed. ∗ This work was supported
by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.
HD 6 5:15 PM
New Nuclear Structure and Decay Results in the 76 Ge- 76 As System
A. R. Domula, D. Gehre, K. Zuber, Technische Universität Dresden, Institut für Kern- und
Teilchenphysik, Zellescher Weg 19, D-01069 Dresden, Germany. J. C. Drohé, N. Nankov, A. J. M.
Plompen, C. Rouki, M. Stanoiu, European Commission, Joint Research Centre, Institute for Reference
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