415 research outputs found

### Total and partial cross sections of the $^{112}$Sn($\alpha,\gamma$)$^{116}$Te reaction measured via in-beam $\gamma$-ray spectroscopy

An extended database of experimental data is needed to address uncertainties
of the nuclear-physics input parameters for Hauser-Feshbach calculations.
Especially $\alpha$+nucleus optical model potentials at low energies are not
well known. The in-beam technique with an array of high-purity germanium (HPGe)
detectors was successfully applied to the measurement of absolute cross
sections of an ($\alpha$,$\gamma$) reaction on a heavy nucleus at sub-Coulomb
energies. The total and partial cross-section values were measured by means of
in-beam $\gamma$-ray spectroscopy. Total and partial cross sections were
measured at four different $\alpha$-particle energies from $E_\alpha = 10.5$
MeV to $E_\alpha = 12$ MeV. The measured total cross-section values are in
excellent agreement with previous results obtained with the activation
technique, which proves the validity of the applied method. The experimental
data was compared to Hauser-Feshbach calculations using the nuclear reaction
code TALYS. A modified version of the semi-microscopic $\alpha$+nucleus optical
model potential OMP 3, as well as modified proton and $\gamma$ widths, are
needed in order to obtain a good agreement between experimental data and
theory. It is found, that a model using a local modification of the
nuclear-physics input parameters simultaneously reproduces total cross sections
of the $^{112}$Sn($\alpha$,$\gamma$) and $^{112}$Sn($\alpha$,p) reactions. The
measurement of partial cross sections turns out to be very important in this
case in order to apply the correct $\gamma$-ray strength function in the
Hauser-Feshbach calculations. The model also reproduces cross-section values of
$\alpha$-induced reactions on $^{106}$Cd, as well as of ($\alpha$,n) reactions
on $^{115,116}$Sn, hinting at a more global character of the obtained
nuclear-physics input.Comment: 8 pages, 9 figure

### Symmetries at and Near Critical Points of Quantum Phase Transitions in Nuclei

We examine several types of symmetries which are relevant to quantum phase
transitions in nuclei. These include: critical-point, quasidynamical, and
partial dynamical symmetries.Comment: 5 pages, 4 figures, Proc. 13th Int. Conf. on "Capture Gamma-Ray
Spectroscopy and Related Topics", August 25-29, 2008, Cologne, German

### Experimental constraints on the $\gamma$-ray strength function in $^{90}$Zr using partial cross sections of the $^{89}$Y(p,$\gamma$)$^{90}$Zr reaction

Partial cross sections of the $^{89}$Y(p,$\gamma$)$^{90}$Zr reaction have
been measured to investigate the $\gamma$-ray strength function in the
neutron-magic nucleus $^{90}$Zr. For five proton energies between $E_p=3.65$
MeV and $E_p=4.70$ MeV, partial cross sections for the population of seven
discrete states in $^{90}$Zr have been determined by means of in-beam
$\gamma$-ray spectroscopy. Since these $\gamma$-ray transitions are dominantly
of $E1$ character, the present measurement allows an access to the low-lying
dipole strength in $^{90}$Zr. A $\gamma$-ray strength function based on the
experimental data could be extracted, which is used to describe the total and
partial cross sections of this reaction by Hauser-Feshbach calculations
successfully. Significant differences with respect to previously measured
strength functions from photoabsorption data point towards deviations from the
Brink-Axel hypothesis relating the photo-excitation and de-excitation strength
functions.Comment: 5 pages, 5 figure

### A method to correct differential nonlinearities in subranging analog-to-digital converters used for digital gamma-ray spectroscopy

The influence on $\gamma$-ray spectra of differential nonlinearities (DNL) in
subranging, pipelined analog-to-digital converts (ADCs) used for digital
$\gamma$-ray spectroscopy was investigated. The influence of the DNL error on
the $\gamma$-ray spectra, depending on the input count-rate and the dynamic
range has been investigated systematically. It turned out, that the DNL becomes
more significant in $\gamma$-ray spectra with larger dynamic range of the
spectroscopy system. An event-by-event offline correction algorithm was
developed and tested extensively. This correction algorithm works especially
well for high dynamic ranges

### Lifetime measurement of excited low-spin states via the $(p,p^{\prime}\gamma$) reaction

In this article a method for lifetime measurements in the sub-picosecond
regime via the Doppler-shift attenuation method (DSAM) following the inelastic
proton scattering reaction is presented. In a pioneering experiment we
extracted the lifetimes of 30 excited low-spin states of $^{96}$Ru, taking
advantage of the coincident detection of scattered protons and de-exciting
$\gamma$-rays as well as the large number of particle and $\gamma$-ray
detectors provided by the SONIC@HORUS setup at the University of Cologne. The
large amount of new experimental data shows that this technique is suited for
the measurement of lifetimes of excited low-spin states, especially for
isotopes with a low isotopic abundance, where $(n,n^{\prime}\gamma$) or - in
case of investigating dipole excitations - ($\gamma,\gamma^{\prime}$)
experiments are not feasible due to the lack of sufficient isotopically
enriched target material

### Elastic alpha-scattering of 112Sn and 124Sn at astrophysically relevant energies

The cross sections for the elastic scattering reactions
{112,124}Sn(a,a){112,124}Sn at energies above and below the Coulomb barrier are
presented and compared to predictions for global alpha-nucleus potentials. The
high precision of the new data allows a study of the global alpha-nucleus
potentials at both the proton and neutron-rich sides of an isotopic chain. In
addition, local alpha-nucleus potentials have been extracted for both nuclei,
and used to reproduce elastic scattering data at higher energies. Predictions
from the capture cross section of the reaction 112Sn(a,g)116Te at
astrophysically relevant energies are presented and compared to experimental
data.Comment: 20 pages, 10 figures, accepted for publication in Phys. Rev.

### $^{187}$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(α , α )106 Cd at several different energies around the Coulomb barrier. The difficulties that arise in the study of 106Cd-α -nuclear potential and the so called Family Problem are addressed in this work

### Q-phonon description of low lying 1^- two-phonon states in spherical nuclei

The properties of 1^-_1 two-phonon states and the characteristics of E1
transition probabilities between low-lying collective states in spherical
nuclei are analysed within the Q-phonon approach to the description of
collective states. Several relations between observables are obtained.
Microscopic calculations of the E1 0^+_1 -> 1^-_1 transition matrix elements
are performed on the basis of the RPA. A satisfactory description of the
experimental data is obtained.Comment: 16 pages, 2 figures, 9 table

- …