Program - Brookhaven National Laboratory

Results of the first complete compilation and evaluation of delayed-neutron emission (including multiple
neutron emission) probabilities and associated half-lives will be presented for all the known beta-delayed
neutron emitters (those for which the Q(β-n) value is positive) in the non-fission region, A ≤ 72. A
total of 101 one-neutron emission probabilities as well as 173 half-lives have been evaluated, with far fewer
evaluated multiple neutron emission probabilities due to a lack of measurements. The recommended values
will be discussed in terms of systematics and available theoretical calculations for the nuclei in this mass
region.
ND 3 11:20 AM
Beta-decay Study of Neutron-Rich Isotopes 93 Br and 93 Kr
K. Miernik, K.P. Rykaczewski, C.J. Gross, D.W. Stracener, A.J. Mendez II, M. Wolińska-Cichocka,
Physics Division, Oak Ridge National Laboratory, Oak Ridge Tennessee 37830 USA. A. Fijalkowska, M.
Karny, A. Korgul, C. Mazzocchi, Faculty of Physics, University of Warsaw, Warsaw PL-00-681, Poland.
R. Grzywacz, D. Miller, L. Cartegni, C.U. Jost, M. Madurga, S.W. Padgett, S.V. Paulauskas, Dept. of
Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA. J.C. Batchelder,
S.H. Liu, Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831, USA. N.T. Brewer, J.H.
Hamilton, J.K. Hwang, A.V. Ramayya, Dept. of Physics and Astronomy, Vanderbilt University,
Nashville, Tennessee 37235, USA. S.V. Ilyushkin, J.A. Winger, Dept. of Physics and Astronomy,
Mississippi State University, Mississippi, 39762, USA. W. Królas, Institute of Nuclear Physics, Polish
Academy of Sciences, Cracow, PL-31-342, Warsaw, Poland. E.F. Zganjar, Dept. of Physics and
Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Half-lives are some of the most fundamental observables for radioactive nuclides. Many nuclear theories aim
to reproduce known values and extrapolate (or predict) these properties for nuclides, which are presently
beyond experimental reach. Nuclear properties may change significantly in non-trivial way when one is
moving away from the valley of stability; therefore, the precise and correct experimental determination
of observables is of great importance for most exotic isotopes. The region around Z = 40 and N =
56 subshell closures is rich in many interesting and surprising nuclear structure features e.g. a sudden
onset of deformation beyond A = 96. The interpretation of many phenomena relies on comparison of
experimental data with theoretical calculation therefore the accurate knowledge of basic observables is
crucial. Additionally some of the proposed r-process scenarios include the nuclides of interest of this work
The calculations of the r-process abundances requires knowledge of both half-life and beta-delayed neutron
branching ratio. We present new studies of 93 Br, 93 Kr and 94 Kr activities. These short-lived neutron
rich nuclei were produced in proton-induced fission of 238 U at the HRIBF facility at Oak Ridge. Their
beta-decays were restudied by means of high resolution on-line mass separator and digital beta-gamma
spectroscopy methods. The half-life value of T 1/2 = 145(10) ms measured for 93 Br is significantly different
from previously adopted T 1/2 =102(10) ms, while the 94 Kr half-life measured to be 210(20) ms agrees
with earlier results. Beta-delayed branching ratio of Pn = 70(10) % derived for 93 Br precursor agrees
with a previously published value of Pn = 68(7) % which was however adopted without an experimental
evidence for the result. The beta-gamma decay properties of 93 Br differ from the previously reported
decay scheme and now include additional gamma transitions of 588 keV and 769 keV following betadelayed
neutron emission. The latest measurement of 93 Kr half-life found in literature dates back to 1976,
the recommended value is T 1/2 =1.289(12) s, in slight discrepancy with our result T 1/2 =1.20(5) s. A
careful analysis of literature points to the possible deficiencies affecting the recommended half-life result.
Research performed as a Eugene P. Wigner Fellow and staff member at the Oak Ridge National Laboratory,
managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract DE-AC05-00OR22725.
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