Program - Brookhaven National Laboratory

specific feature of the procedure employed was adjusting of free model parameters to fit both the available
differential cross-section data and thick target yields measured with a thick uniform silicon target. The
measurements were performed using the Tandetron accelerator of Surrey University Ion Beam Centre.
Such an approach made it possible to adjust resonance widths for narrow resonances in the cases when
the cross-section structure was measured with insufficient energy resolution. The evaluated differential
Si( 4 He, 4 He)Si cross-section in the energy range up to 8 MeV will be made available to the community
through the on-line SigmaCalc calculator at http://www-nds.iaea.org/sigmacalc/.
Corresponding author: C. Jeynes
Session HD Nuclear Structure and Decay
Tuesday March 5, 2013
Room: Empire West at 3:30 PM
HD 1 3:30 PM
Decay Studies of 238U Fission Products at the HRIBF (Oak Ridge)*
K.P. Rykaczewski
Physics Division, ORNL
A summary of many studies on the decay of neutron-rich nuclei performed at the Holifield Radioactive
Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory will be given. Examples of the impact of
the results on nuclear structure, astrophysics and applied studies will be discussed. Beams of neutron-rich
nuclei were produced at the HRIBF using high-resolution on-line mass separation [Beene2011] following
proton-induced fission of 238U. Several techniques were used to enhance the isobaric purity of these beams:
charge exchange, molecular extraction of GeS and AsS [Stracener2003], laser resonance ionization of Ga
[Liu2012], and post-acceleration followed by ranging-out in gas of the mono-energetic beam components
[Gross2005]. Decay of very neutron-rich isotopes of several elements between Z = 29 Cu and Z = 63 Eu
were studied u sing beta-gamma-neutron spectroscopy methods, mostly at the Low-energy Radioactive Ion
Beam Spectroscopy Station (LeRIBSS) [Rykaczewski2009]. The results include the first determination of
half-life for 82Zn, 83Zn, 85Ga [Madurga2012], 86Ga [Grzywacz2012], and 86Ge [Mazzocchi2012] as well as a
new measurement of the 93Br half-life [Miernik2012] that is in conflict with the adopted value. Several betagamma
and beta-n-gamma decay schemes were obtained for the first time or greatly expanded, e.g., 73Cu
[Paulauskas2012] through 75Cu [Ilyushkin2011] and 77Cu [Ilyushkin 2009], up to N=50 79Cu [Korgul2012].
The experiments with post-accelerated negative ions of Cu and Ga [Winger2009, Winger2010, Korgul2012]
and with positive ions of Zn [Padgett2010] and Br [Miernik2012] resulted in the precise determination of
absolute beta-delayed branching ratios that are in many cases, substantially larger than previously reported.
The HRIBF studies of beta-delayed neutron emission were enhanced recently by the measurement of the
energy of the neutrons. Decays of over 25 beta-delayed neutron precursors were measured with the timeof-flight
neutron array Versatile Array for Neutron Detection at Low Energy (VANDLE) [Grzywacz2012a]
at LeRIBSS allowing us to study the beta-strength function distribution above the neutron separation
energies in daughter nuclei. Studies of the beta-strength function were expanded by measurements using the
recently commissioned Modular Total Absorption Spectrometer (MTAS) [Rykaczewski2012]. MTAS is the
first segmented total absorption array having an active volume at least seven times larger than any previous
spectrometer resulting in superior efficiency [Wolinska2013]. The decays of over 20 fission products have
been measured at the HRIBF with MTAS [Karny2013]. Activities included 86Br, 87Br, 89Kr, 90Kr, 137I,
137Xe and 139Xe that are listed among highest priority nuclei for decay heat measurements established by
the OECD Nuclear Energy Agency assessment [NEA2007]. The comparison of the spectra and the MTAS
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