1,128 research outputs found
Total reaction cross sections from 141Pr(,)Pr elastic scattering and -induced reaction cross sections at low energies
Elastic scattering data for Pr(,)Pr have been
analyzed to derive a new energy-dependent local potential for the
Pr- system. This potential is used successfully to predict the
cross section of the Pr(,n)Pm reaction at low energies
where new experimental data have become available very recently. Contrary to
various global potentials, this new potential is able to reproduce
simultaneously elastic scattering data around and above the Coulomb barrier and
reaction data below the Coulomb barrier for the Pr- system.
Reasons for the partial failure of the global potentials are explained by
intrinsic properties of the scattering matrix and their variation with energy.
The new local potential may become the basis for the construction of a new
global -nucleus potential.Comment: 12 pages, 8 figures, Phys. Rev. C, accepte
Challenges in nucleosynthesis of trans-iron elements
© 2014 Author(s).. All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.Nucleosynthesis beyond Fe poses additional challenges not encountered when studying astrophysical processes involving light nuclei. Astrophysical sites and conditions are not well known for some of the processes involved. On the nuclear physics side, different approaches are required, both in theory and experiment. The main differences and most important considerations are presented for a selection of nucleosynthesis processes and reactions, specifically the s-, r-, γ-, and νp-processes. Among the discussed issues are uncertainties in sites and production conditions, the difference between laboratory and stellar rates, reaction mechanisms, important transitions, thermal population of excited states, and uncertainty estimates for stellar rates. The utility and limitations of indirect experimental approaches are also addressed. The presentation should not be viewed as confining the discussed problems to the specific processes. The intention is to generally introduce the concepts and possible pitfalls along with some examples. Similar problems may apply to further astrophysical processes involving nuclei from the Fe region upward and/or at high plasma temperatures. The framework and strategies presented here are intended to aid the conception of future experimental and theoretical approaches.Peer reviewe
70Ge(p,gamma)71As and 76Ge(p,n)76As cross sections for the astrophysical p process: sensitivity of the optical proton potential at low energies
The cross sections of the 70Ge(p,gamma)71As and 76Ge(p,n)76As reactions have
been measured with the activation method in the Gamow window for the
astrophysical p process. The experiments were carried out at the Van de Graaff
and cyclotron accelerators of ATOMKI. The cross sections have been derived by
measuring the decay gamma-radiation of the reaction products. The results are
compared to the predictions of Hauser-Feshbach statistical model calculations
using the code NON-SMOKER. Good agreement between theoretical and experimental
S factors is found. Based on the new data, modifications of the optical
potential used for low-energy protons are discussed.Comment: Accepted for publication in Phys. Rev.
Precise half-life measurement of 110Sn and 109In isotopes
The half-lives of 110Sn and 109In isotopes have been measured with high
precision. The results are T1/2 =4.173 +- 0.023 h for 110Sn and T1/2 = 4.167
+-0.018 h for 109In. The precision of the half-lives has been increased by a
factor of 5 with respect to the literature values which makes results of the
recently measured 106Cd(alpha,gamma)110Sn and 106Cd(alpha,p)109In cross
sections more reliable.Comment: 3 pages, 2 figures, accepted for publication in Phys. Rev C as brief
repor
Measurements of Gd 152 (p,γ) Tb 153 and Gd 152 (p,n) Tb 152 reaction cross sections for the astrophysical γ process
The total cross sections for the Gd152(p,γ)Tb153 and Gd152(p,n)152Tb reactions have been measured by the activation method at effective center-of-mass energies 3.47≤Ec.m.eff≤7.94 MeV and 4.96≤Ec.m.eff≤7.94 MeV, respectively. The targets were prepared by evaporation of 30.6% isotopically enriched Gd152 oxide on aluminum backing foils, and bombarded with proton beams provided by a cyclotron accelerator. The cross sections were deduced from the observed γ-ray activity, which was detected off-line by an HPGe detector in a low background environment. The results are presented and compared with predictions of statistical model calculations. This comparison supports a modified optical proton+Gd152 potential suggested earlier.Peer reviewedFinal Accepted Versio
First Principles Study of Adsorption of on Al Surface with Hybrid Functionals
Adsorption of molecule on Al surface has been a long standing puzzle
for the first principles calculation. We have studied the adsorption of
molecule on the Al(111) surface using hybrid functionals. In contrast to the
previous LDA/GGA, the present calculations with hybrid functionals successfully
predict that molecule can be absorbed on the Al(111) surface with a
barrier around 0.20.4 eV, which is in good agreement with
experiments. Our calculations predict that the LUMO of molecule is
higher than the Fermi level of the Al(111) surface, which is responsible for
the barrier of the adsorption.Comment: 14 pages, 5 figure
Coulomb suppression of the stellar enhancement factor
It is commonly assumed that reaction measurements for astrophysics should be
preferably performed in the direction of positive Q value to minimize the
impact of the stellar enhancement factor, i.e. the difference between the
laboratory rate and the actual stellar rate. We show that the stellar effects
can be minimized in the charged particle channel, even when the reaction Q
value is negative. As a demonstration, the cross section of the astrophysically
relevant 85Rb(p,n)85Sr reaction has been measured by activation between 2.16 <
Ec.m. < 3.96 MeV and the astrophysical reaction rate for (p,n) as well as (n,p)
is directly inferred from the data. The presented arguments are also relevant
for other alpha and proton-induced reactions in the p and rp processes.
Additionally, our results confirm a previously derived modification of a global
optical proton potential.Comment: submitted to PR
Alpha-induced cross sections of 106Cd for the astrophysical p-process
The 106Cd(alpha,gamma)110Sn reaction cross section has been measured in the
energy range of the Gamow window for the astrophysical p-process scenario. The
cross sections for 106Cd(alpha,n)109Sn and for 106Cd(alpha,p)109In below the
(alpha,n) threshold have also been determined. The results are compared with
predictions of the statistical model code NON-SMOKER using different input
parameters. The comparison shows that a discrepancy for 106Cd(alpha,gamma)110Sn
when using the standard optical potentials can be removed with a different
alpha+106Cd potential. Some astrophysical implications are discussed.Comment: 10 pages, 9 figures, accepted for publication in Phys. Rev
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