370 research outputs found

### Neutron activation of natural zinc samples at kT = 25 keV

The neutron-capture cross sections of 64Zn, 68Zn, and 70Zn have been measured
with the activation technique in a quasistellar neutron spectrum corresponding
to a thermal energy of kT = 25 keV. By a series of repeated irradiations with
different experimental conditions, an uncertainty of 3% could be achieved for
the 64Zn(n,g)65Zn cross section and for the partial cross section
68Zn(n,g)69Zn-m feeding the isomeric state in 69Zn. For the partial cross
sections 70Zn(n,g)71Zn-m and 70Zn(n,g)71Zn-g, which had not been measured so
far, uncertainties of only 16% and 6% could be reached because of limited
counting statistics and decay intensities. Compared to previous measurements on
64,68Zn, the uncertainties could be significantly improved, while the 70Zn
cross section was found to be two times smaller than existing model
calculations. From these results Maxwellian average cross sections were
determined between 5 and 100 keV. Additionally, the beta-decay half-life of
71Zn-m could be determined with significantly improved accuracy. The
consequences of these data have been studied by network calculations for
convective core He burning and convective shell C burning in massive stars

### $^{187}$Re(\gamm,n) cross section close to and above the neutron threshold

The neutron capture cross section of the unstable nucleus $^{186}$Re is
studied by investigating the inverse photodisintegration reaction
$^{187}$Re($\gamma$,n). The special interest of the {\it s}-process branching
point $^{186}$Re is related to the question of possible {\it s}-process
contributions to the abundance of the {\it r}-process chronometer nucleus
^{187}$Re. We use the photoactivation technique to measure photodisintegration
rates. Our experimental results are in good agreement with two different
statistical model calculations. Although the cross sections predicted by both
models for the inverse reaction$^{186}$Re(n,$\gamma$) is too low to remove the
overproduction of$^{186}$Os; the two predicted neutron-capture cross sections
differ by a factor of 2.4; this calls for future theoretical study.Comment: Phys. Rev. C, in pres

### How important is the Family? : Alpha nuclear potentials and p-process nucleosynthesis

Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike LicenceIn this work we present the results from the analysis of the experimentally measured angular distributions of the reaction 106Cd(Î± , Î± )106 Cd at several different energies around the Coulomb barrier. The difficulties that arise in the study of 106Cd-Î± -nuclear potential and the so called Family Problem are addressed in this work

### Kabul Times (April 11, 1964, vol. 3, no. 37)

High-resolution photon scattering experiments have been performed on the nucleus 45Sc at the Darmstadt superconducting electron accelerator S-DALINAC using bremsstrahlung beams with end point energies of 5.0 and 7.0MeV. Energies, absolute cross-sections and decay widths of 50 states, most of them previously unknown, have been determined. The results are compared to (Î³,$\gamma{^\prime}$) experiments on the neighbouring closed proton shell isotope 44Ca

### The s-process branching at 185W

The neutron capture cross section of the unstable nucleus 185W has been
derived from experimental photoactivation data of the inverse reaction
186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the
theoretically predicted neutron capture cross section of 185W of sigma = 700
mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n =
(3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching.
In a stellar s-process model one finds a significant overproduction of the
residual s-only nucleus 186Os.Comment: ApJ, in pres

### Predicted cross sections for photon-induced particle emission

Cross sections for the photon-induced particle-emission reactions (gamma,n),
(gamma,p), and (gamma,alpha) are given for all natural isotopes from Ti to Bi.
The target nuclei are assumed to be in their ground states, except for 180Ta
which is naturally occurring as the isomer 180mTa. The cross sections are
calculated in a statistical model (Hauser-Feshbach) approach and covering an
energy range from threshold up to 7.35 MeV above the threshold (14.7 MeV above
threshold for (gamma,alpha) reactions). The results are intended to aid
conception and analysis of experiments which can also be used to test the
methods involved in predicting astrophysical reaction rates for
nucleosynthesis.Comment: 74 pages (including three long tables), accepted for publication in
Atomic Data Nuclear Data Tables, corrected header of Table

### High precision $^{89}$Y($\alpha$,$\alpha$)$^{89}$Y scattering at low energies

Elastic scattering cross sections of the $^{89}$Y($\alpha$,$\alpha$)$^{89}$Y
reaction have been measured at energies E$_{c.m.}$ = 15.51 and 18.63 MeV. The
high precision data for the semi-magic $N = 50$ nucleus $^{89}$Y are used to
derive a local potential and to evaluate the predictions of global and regional
$\alpha$-nucleus potentials. The variation of the elastic alpha scattering
cross sections along the $N = 50$ isotonic chain is investigated by a study of
the ratios of angular distributions for $^{89}$Y($\alpha$,$\alpha$)$^{89}$Y and
$^{92}$Mo($\alpha$,$\alpha$)$^{92}$Mo at E$_{c.m.} \approx$ 15.51 and 18.63
MeV. This ratio is a very sensitive probe at energies close to the Coulomb
barrier, where scattering data alone is usually not enough to characterize the
different potentials. Furthermore, $\alpha$-cluster states in $^{93}$Nb =
$^{89}$Y $\otimes$ $\alpha$ are investigated

### Cross-section measurement of the Ba 130 (p,Î³) La 131 reaction for Î³ -process nucleosynthesis

Background: Deviations between experimental data of charged-particle-induced reactions and calculations within the statistical model are frequently found. An extended data base is needed to address the uncertainties regarding the nuclear-physics input parameters in order to understand the nucleosynthesis of the neutron-deficient p nuclei. Purpose: A measurement of total cross-section values of the Ba130(p,Î³)La131 reaction at low proton energies allows a stringent test of statistical model predictions with different proton+nucleus optical model potentials. Since no experimental data are available for proton-capture reactions in this mass region around A â‰ˆ130, this measurement can be an important input to test the global applicability of proton+nucleus optical model potentials. Method: The total reaction cross-section values were measured by means of the activation method. After the irradiation with protons, the reaction yield was determined by use of Î³-ray spectroscopy using two clover-type high-purity germanium detectors. In total, cross-section values for eight different proton energies could be determined in the energy range between 3.6 MeV â‰¤Epâ‰¤ 5.0 MeV, thus, inside the astrophysically relevant energy region. Results: The measured cross-section values were compared to Hauser-Feshbach calculations using the statistical model codes TALYS and SMARAGD with different proton+nucleus optical model potentials. With the semimicroscopic JLM proton+nucleus optical model potential used in the SMARAGD code, the absolute cross-section values are reproduced well, but the energy dependence is too steep at the lowest energies. The best description is given by a TALYS calculation using the semimicroscopic Bauge proton+nucleus optical model potential using a constant renormalization factor. Conclusions: The statistical model calculation using the Bauge semimicroscopic proton+nucleus optical model potential deviates by a constant factor of 2.1 from the experimental data. Using this model, an experimentally supported stellar reaction rate for proton capture on the p nucleus Ba130 was calculated. At astrophysical temperatures, an increase in the stellar reaction rate of 68% compared to rates obtained from the widely used NON-SMOKER code is found. This measurement extends the scarce experimental data base for charged-particle-induced reactions, which can be helpful to derive a more globally applicable proton+nucleus optical model potential.Peer reviewedFinal Accepted Versio

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