320
M. Wiedeking
3.2 Pygmy Dipole Resonance
Studies of the PSF and NLD are mainly concerned with determining the overall
electromagnetic decay (and excitation) properties of a nucleus, but researchers at
iThemba LABS are also interested in understanding particular nuclear structure
aspects, such as the GEDR and the PDR, that define the structure of the PSF. While
the PDR has been studied for a range of nuclei, spanning several mass regions, its
nature and evolution with deformation is not understood. While the PDR has be
studied in 74 Ge with a combination of particle telescopes and AFRODITE [5], the
available equipment is ideally suited for an experimental investigation of the PDR
with the use of the K600 magnetic spectrometer at zero degrees, coupled to an array
of γ-ray detectors, and an experimental program is underway to study the PDR in
deformed nuclei (L. Pellegri, private communications).
3.3 138 La
Researchers at iThemba LABS have measured the PSFs and NLDs for 138,139,140 La
at the Oslo Cyclotron Laboratory (OCL) [6]. The Maxwellian-averaged cross
sections (MACS) were calculated and from these the (γ, n) production rates were
found. The results show that the 139 La(γ,n) 138 La production rate is smaller than the
138 La(γ,n) 137 La destruction rate. Through this new determination of the reaction
rates the conclusion is made that 138 La cannot be produced by photoreactions during
the p-process and instead the neutrino process is the dominant production process
for 138 La [7].
3.4 180 Ta
The PSFs and NLDs were measured for 180,181,182 Ta [8] at the OCL and used as
input parameters in the TALYS reaction code [9] to calculate (n, γ) cross sections.
From these the MACS and reaction rates of astrophysical interest are obtained. The
latter is used in s-process calculations and p-process simulations to re-estimate the
nucleosynthesis of 180 Ta in light of the new experimental data [10]. The results show
that the s-process contribution in the production of 180 Ta is negligible and instead
the p-process is the primary production mechanism of nature’s rarest stable isotope.
Acknowledgements Support from the National Research Foundation (South Africa) and the
IAEA under Research Contract 20454 is greatly appreciated.
M. Wiedeking
3.2 Pygmy Dipole Resonance
Studies of the PSF and NLD are mainly concerned with determining the overall
electromagnetic decay (and excitation) properties of a nucleus, but researchers at
iThemba LABS are also interested in understanding particular nuclear structure
aspects, such as the GEDR and the PDR, that define the structure of the PSF. While
the PDR has been studied for a range of nuclei, spanning several mass regions, its
nature and evolution with deformation is not understood. While the PDR has be
studied in 74 Ge with a combination of particle telescopes and AFRODITE [5], the
available equipment is ideally suited for an experimental investigation of the PDR
with the use of the K600 magnetic spectrometer at zero degrees, coupled to an array
of γ-ray detectors, and an experimental program is underway to study the PDR in
deformed nuclei (L. Pellegri, private communications).
3.3 138 La
Researchers at iThemba LABS have measured the PSFs and NLDs for 138,139,140 La
at the Oslo Cyclotron Laboratory (OCL) [6]. The Maxwellian-averaged cross
sections (MACS) were calculated and from these the (γ, n) production rates were
found. The results show that the 139 La(γ,n) 138 La production rate is smaller than the
138 La(γ,n) 137 La destruction rate. Through this new determination of the reaction
rates the conclusion is made that 138 La cannot be produced by photoreactions during
the p-process and instead the neutrino process is the dominant production process
for 138 La [7].
3.4 180 Ta
The PSFs and NLDs were measured for 180,181,182 Ta [8] at the OCL and used as
input parameters in the TALYS reaction code [9] to calculate (n, γ) cross sections.
From these the MACS and reaction rates of astrophysical interest are obtained. The
latter is used in s-process calculations and p-process simulations to re-estimate the
nucleosynthesis of 180 Ta in light of the new experimental data [10]. The results show
that the s-process contribution in the production of 180 Ta is negligible and instead
the p-process is the primary production mechanism of nature’s rarest stable isotope.
Acknowledgements Support from the National Research Foundation (South Africa) and the
IAEA under Research Contract 20454 is greatly appreciated.