Strong enhancement of level densities in the crossover from spherical to deformed neodymium isotopes

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La 137,138,139 (n,γ) cross sections constrained with statistical decay properties of la 138,139,140 nuclei

The nuclear level densities and γ-ray strength functions of La138,139,140 were measured using the La139(He3,α), La139(He3,He3′), and La139(d,p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A∼140 region is discussed. The La137,138,139(n,γ) cross sections were calculated at s- and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. Good agreement is found between La139(n,γ) calculated cross sections and previous measurements.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

New experimental constraint on the 185W(n,γ)186W cross section

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New experimental constraint on the W-185(n, & gamma;) W-186 cross section

In this work, we present new data on the 182,183,184W(; gamma; , n) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and ; gamma; -ray strength function of 186W from data on the 186W(; alpha;, ; alpha;'; gamma; ) 186W reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the 186W(; gamma; , n) cross section with our new 182,183,184W(; gamma; , n) and (; alpha;, ; alpha;'; gamma; ) 186W data sets, we have deduced the 186W ; gamma; -ray strength function in the range of 1 E ; gamma; 6 MeV and 7 E ; gamma; 14 MeV. Our data are used to extract the level density and ; gamma; -ray strength functions needed as input to the nuclear-reaction code TALYS, providing an indirect, experimental constraint for the 185W(n, ; gamma; ) 186W cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 database, our results are on average lower for the relevant energy range kBT ; ISIN; [5, 100] keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao et al. [At. Data Nucl. Data Tables 76, 70 (2000)] and the cross section experimentally constrained on photoneutron data of Sonnabend et al. [Astrophys. J. 583, 506 (2003)] are significantly higher than our result. The lower value ingredient in simulations for investigating the neutron density and the 186,187Os production in the s process.European Research Council [325714]; Research Council of Norway [OISE-1927130, 118846]; F.R.S.-FNRS; National Science Foundation [316116]; National Research Foundation of South Africa; [637686]The authors would like to thank J. C. Mueller, P. A. Sobas, and J. C. Wikne at the Oslo Cyclotron Laboratory for operating the cyclotron and providing excellent experimental conditions. We sincerely thank T. W. Hagen, S. J. Rose, and F. Zeiser for helping with the OCL experiment, Y. -W. Lui for helping with the NewSUBARU experiments, and S. N. Liddick for inspiring discussions. A.C.L. gratefully acknowledges funding of this research by the European Research Council through ERC-STG-2014 under Grant Agreement No. 637686, and from the Research Council of Norway, Project Grant No. 316116. S.G. acknowledges the support from the F.R.S.-FNRS. This work was supported in part by the National Science Foundation under Grant No. OISE-1927130 (IReNA) . The photoneutron cross section measurement was performed as part of the IAEA CRP on Updating the Photonuclear Data Library and generating a Reference Database for Photon Strength Functions (F41032) . A.G., V.W.I., and S.S. gratefully acknowledge financial support from the Research Council of Norway, Project Grant No. 325714. This work is in part based on the research supported partly by the National Research Foundation of South Africa (Grant No. 118846)

Experimental observation of the M1 scissors mode in 254^{254}No

International audienceWe present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb(48Ca, ))254No reaction. The spectrum of γ rays emitted by the excited 254No nuclei shows an enhanced γ-ray yield for transition energies of ≈2.5 MeV. By measuring the linear polarization properties of the emitted γ rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced γ-ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an M1 component in the γ strength function with total strength . This is in good agreement with the integrated M1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei. (Elsevier B.V.