224 research outputs found
KADoNiS-: The astrophysical -process database
The KADoNiS- project is an online database for cross sections relevant to
the -process. All existing experimental data was collected and reviewed.
With this contribution a user-friendly database using the KADoNiS (Karlsruhe
Astrophysical Database of Nucleosynthesis in Stars) framework is launched,
including all available experimental data from (p,), (p,n),
(p,), (,), (,n) and (,p) reactions in
or close to the respective Gamow window with cut-off date of August 2012
(www.kadonis.org/pprocess).Comment: Proceedings Nuclear Data Conference 2013, published in Nuclear Data
Sheets 120 (2014) 19
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
Successful Prediction of Total α-Induced Reaction Cross Sections at Astrophysically Relevant Sub-Coulomb Energies Using a Novel Approach
The prediction of stellar (,) reaction rates for heavy nuclei
is based on the calculation of (,) cross sections at
sub-Coulomb energies. These rates are essential for modeling the
nucleosynthesis of so-called -nuclei. The standard calculations in the
statistical model show a dramatic sensitivity to the chosen -nucleus
potential. The present study explains the reason for this dramatic sensitivity
which results from the tail of the imaginary -nucleus potential in the
underlying optical model calculation of the total reaction cross section. As an
alternative to the optical model, a simple barrier transmission model is
suggested. It is shown that this simple model in combination with a well-chosen
-nucleus potential is able to predict total -induced reaction
cross sections for a wide range of heavy target nuclei above
with uncertainties below a factor of two. The new predictions from the simple
model do not require any adjustment of parameters to experimental reaction
cross sections whereas in previous statistical model calculations all
predictions remained very uncertain because the parameters of the
-nucleus potential had to be adjusted to experimental data. The new
model allows to predict the reaction rate of the astrophysically important
W(,)Os reaction with reduced uncertainties,
leading to a significantly lower reaction rate at low temperatures. The new
approach could also be validated for a broad range of target nuclei from up to .Comment: 6 pages, 3 figures; 6 pages supplement with 3 additional figures and
3 tables; Physical Review Letters, accepted for publicatio
Direct study of the alpha-nucleus optical potential at astrophysical energies using the 64Zn(p,alpha)61Cu reaction
In the model calculations of heavy element nucleosynthesis processes the
nuclear reaction rates are taken from statistical model calculations which
utilize various nuclear input parameters. It is found that in the case of
reactions involving alpha particles the calculations bear a high uncertainty
owing to the largely unknown low energy alpha-nucleus optical potential.
Experiments are typically restricted to higher energies and therefore no direct
astrophysical consequences can be drawn. In the present work a (p,alpha)
reaction is used for the first time to study the alpha-nucleus optical
potential. The measured 64Zn(p,alpha)61Cu cross section is uniquely sensitive
to the alpha-nucleus potential and the measurement covers the whole
astrophysically relevant energy range. By the comparison to model calculations,
direct evidence is provided for the incorrectness of global optical potentials
used in astrophysical models.Comment: Accepted for publication in Physical Review C as a Rapid
Communicatio
Investigation of alpha-induced reactions on 130Ba and 132Ba and their importance for the synthesis of heavy p nuclei
Captures of alpha particles on the proton-richest Barium isotope, 130Ba, have
been studied in order to provide cross section data for the modeling of the
astrophysical gamma process. The cross sections of the 130Ba(alpha,gamma)134Ce
and 130Ba(alpha,n)133Ce reactions have been measured with the activation
technique in the center-of mass energy range between 11.6 and 16 MeV, close
above the astrophysically relevant energies. As a side result, the cross
section of the 132Ba(alpha,n)135Ce reaction has also been measured. The results
are compared with the prediction of statistical model calculations, using
different input parameters such as alpha+nucleus optical potentials. It is
found that the (alpha,n) data can be reproduced employing the standard
alpha+nucleus optical potential widely used in astrophysical applications.
Assuming its validity also in the astrophysically relevant energy window, we
present new stellar reaction rates for 130Ba(alpha,gamma)134Ce and
132Ba(alpha,gamma)136Ce and their inverse reactions calculated with the SMARAGD
statistical model code. The highly increased 136Ce(gamma,alpha)132Ba rate
implies that the p nucleus 130Ba cannot directly receive contributions from the
Ce isotopic chain. Further measurements are required to better constrain this
result.Comment: Accepted for publication in Phys. Rev.
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