Program - Brookhaven National Laboratory

espectively, and identified approximately 200 69 Kr implantation-decay events. We observed a dominant
β-decay branch to the isobaric analog state (IAS) in 69 Br which then decays to the first excited state
in 68 Se, a decay path which strongly constrains the spin and mass of 69 Kr. Our measured IAS energy,
however, disagrees by approximately 1 MeV from the previously adopted value of 4.07(5) MeV [2]. Data
from this work represents new measurements that are valuable for updating ENSDF, RIPL, and decay
databases, as well as for clarifying existing ambiguities. An overview of the results from our analysis of
implanted neutron-deficient nuclei and their implications will be presented. ⋆ This work is supported by
the U.S. DOE Office of Nuclear Physics, Contract No. DE- AC02-06CH11357.
[1] H. Schatz et al., Phys. Rep. 96 (1998). [2] X.J. Xu et al., Phys. Rev. C 55, R553 (1997).
LB 7 5:30 PM
The (n, α) Reaction in the S-Process Branching Point 59 Ni
C. Weiss, C. Guerrero, The n TOF collaboration
Vienna University of Technology, Vienna, Austria, CERN, Geneva, Switzerland,
https://ntof-exp.web.cern.ch/ntof-exp/
The (n, α) reaction in the radioactive 59 Ni is of relevance in nuclear astrophysics as it can be considered
as the first branching point in the astrophysical s-process. Its relevance in nuclear technology is especially
related to material embrittlement in stainless steel. However, there is a strong discrepancy between available
experimental data and the evaluated nuclear data files for this reaction. At the n TOF facility at CERN,
a dedicated system based on sCVD diamond detectors was setup to measure the 59 Ni(n, α) cross section.
The results of this measurement, with special emphasis on the dominant resonance at 203 eV, will be
presented. CIVIDEC Instrumentation GmbH, Vienna, Austria, sponsored this work.
LB 8 5:45 PM
Uncertainties in Astrophysical β-decay Rates from the FRDM
M. G. Bertolli, P. Möller
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
S. Jones
Astrophysics Group, Lennard Jones Building, Keele University, ST5 5BG, UK
β − -decay rates are of crucial importance in stellar evolution and nucleosynthesis, as they are a key component
in stellar processes. Tabulated values of the decay rates as a function of both temperature T and
density ρ are necessary input to stellar evolution codes such as MESA [1], or large-scale nucleosynthesis
simulations such as those performed by the NuGrid collaboration [2]. It is therefore of interest to know
the uncertainties on the nuclear reaction rates and the effects of these uncertainties on stellar structure
and isotopic yields. At Los Alamos National Laboratory, β-strength functions and reaction rates for nuclei
ranging from 16 O to 339 136 and extending from the proton drip line to the neutron drip line are calculated
from the starting point of nuclear ground-state masses and deformations based on the finite-range droplet
model [3, 4]. In this work we investigate the effect of model uncertainty on astrophysical β − -decay rates
from Ref. [4]. The sources of uncertainty considered are Q values and deformation for more than 5,000
nuclei with transitions from ground-state in the parent to excited-states in the daughter. The rates and
their uncertainties are generated for a variety of temperature and density ranges, corresponding to key
stellar processes. We demonstrate the effects of these rate uncertainties on isotopic abundances using the
NuGrid network calculations.
172