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Register a new user$gamma$-ray Strength Function for Barium Isotopes
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Photoneutron cross sections were measured for $^{137}$Ba and $^{138}$Ba at energies below two-neutron threshold using quasi-monochromatic $gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. The photoneutron data are used to constrain the $gamma$-ray strength function on the basis of the Hartree-Fock-Bogolyubov plus quasi-particle random phase approximation using the Gogny D1M interaction. Supplementing the experimentally constrained $gamma$-ray strength function with the zero-limit E1 and M1 contributions which are unique to the deexcitation mode, we discuss radiative neutron capture cross sections relevant to the s-process nucleosynthesis of barium isotopes in the vicinity of the neutron magic number 82.
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Photoneutron cross sections were measured for $^{203}$Tl and $^{205}$Tl at energies between the one- and two-neutron thresholds using quasi-monochromatic $gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. Our new measurement results in cross sections significantly different from the previously reported bremsstrahlung experiment, leading to rather different GDR parameters, in particular to lower GDR peak energies and higher peak cross sections. The photoneutron data are used to constrain the $gamma$-ray strength function on the basis of the Hartree-Fock-Bogolyubov plus quasi-particle random phase approximation using the Gogny D1M interaction. Supplementing the experimentally constrained $gamma$-ray strength function with the zero-limit E1 and M1 contributions for the de-excitation mode, we estimate the Maxwellian-averaged cross section for the s-process branching-point nucleus $^{204}$Tl in the context of the $^{205}$Pb - $^{205}$Tl chronometry.
The level densities and $gamma$-ray strength functions of $^{105,106,111,112}$Cd have been extracted from particle-$gamma$ coincidence data using the Oslo method. The level densities are in very good agreement with known levels at low excitation energy. The $gamma$-ray strength functions display no strong enhancement for low $gamma$ energies. However, more low-energy strength is apparent for $^{105,106}$Cd than for $^{111,112}$Cd. For $gamma$ energies above $approx$ 4 MeV, there is evidence for some extra strength, similar to what has been previously observed for the Sn isotopes. The origin of this extra strength is unclear; it might be due to $E1$ and $M1$ transitions originating from neutron skin oscillations or the spin-flip resonance, respectively.
The gamma-strength functions and level densities in the quasi-continuum of 147;149Sm isotopes have been extracted from particle-coincidences using the Oslo method. The nuclei of interest were populated via (p,d) reactions on pure 148;150Sm targets and the reaction products were recorded by the Hyperion array. An upbend in the low-energy region of the gSF has been observed. The systematic analysis of the gSF for a range of Sm isotopes highlights the interplay between scissors mode and the upbend. Shell-model calculations show reasonable agreement with the experimental gSFs and confirm the correspondence between the upbend and scissors mode.
The nuclear level density and the gamma-ray strength function have been determined for 43Sc in the energy range up to 2 MeV below the neutron separation energy using the Oslo method with the 46Ti(p,alpha)43Sc reaction. A comparison to 45Sc shows that the level density of 43Sc is smaller by an approximately constant factor of two. This behaviour is well reproduced in a microscopical/combinatorial model calculation. The gamma-ray strength function is showing an increase at low gamma-ray energies, a feature which has been observed in several nuclei but which still awaits theoretical explanation.
In this work, we present new data on the $^{89}$Y($gamma$,n) cross section studied with a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility in Japan contributing torwards resolving a long standing discrepancy between existing measurements of this cross section. Results for $gamma$-ray strength function below threshold obtained by applying the Oslo method to $^{89}$Y($p,pgamma$)$^{89}$Y coincidences combined with the $^{89}$Y($gamma$,n) data this providing experimental data for the $gamma$-ray strength function of $^{89}$Y for $gamma$ energies in the range of $approx 1.6$ Mev to $approx$ 20 MeV. A low-energy enhancement is seen for $gamma$-rays below $approx 2.5$ MeV. Shell-model calculations indicate that this feature is caused by strong, low-energy $M1$ transitions at high excitation energies. The nuclear level density and $gamma$-ray strength function have been extracted from $^{89}$Y($d,p gamma$)$^{90}$Y coincidences using the Oslo method. Using the ($gamma,n$) and ($d,pgamma$) data as experimental constraints, we have calculated the $^{89}$Y($n,gamma$)$^{90}$Y cross section with the TALYS reaction code. Our results have been compared with directly measured (n,$gamma$) cross sections and evaluations. The $N=50$ isotope $^{89}$Y is an important bottleneck in the s-process and the magnitude of the $^{89}$Y(n,$gamma)$ cross section is key to understanding how s-process stars produce heavy isotopes.
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