arXiv subjects

Therese Renstrøm

Publications and source records attributed to Therese Renstrøm.

4 recordsLinked to original sources

arXiv2021

A new software implementation of the Oslo method with rigorous statistical uncertainty propagation

The Oslo method comprises a set of analysis techniques designed to extract nuclear level density and average $γ$-decay strength function from a set of excitation-energy tagged $γ$-ray spectra. Here we present a new software implementation of the entire Oslo method, called OMpy. We provide a summary of the theoretical basis and derive the essential equations used in the Oslo method. In addition to the functionality of the original analysis code, the new implementation includes novel components such as a rigorous method to propagate uncertainties throughout all steps of the Oslo method using a Monte Carlo approach. The resulting level density and $γ$-ray strength function have to be normalized to auxiliary data. The normalization is performed simultaneously for both quantities, thus preserving all correlations. The software is verified by the analysis of a synthetic spectrum and compared to the results of the previous implementation, the oslo-method-software.

physics.comp-ph↗

arXiv2017

$^{137,138,139}$La($n$, $γ$) cross sections constrained with statistical decay properties of $^{138,139,140}$La nuclei

The nuclear level densities and $γ$-ray strength functions of $^{138,139,140}$La were measured using the $^{139}$La($^{3}$He, $α$), $^{139}$La($^{3}$He, $^{3}$He$^\prime$) and $^{139}$La(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$\sim$140 region is discussed. The $^{137,138,139}$La($n, γ)$ 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 $^{139}$La($n, γ)$ calculated cross sections and previous measurements.

nucl-ex↗

arXiv2014

Pygmy resonance and low-energy enhancement in the $γ$-ray strength functions of Pd~isotopes

An unexpected enhancement in the $γ$-ray strength function, as compared to the low energy tail of the Giant Dipole Resonance (GDR), has been observed for Sc, Ti, V, Fe and Mo isotopes for $E_γ<4$ MeV. This enhancement was not observed in subsequent analyses on Sn isotopes, but a Pygmy Dipole Resonance (PDR) centered at $E_γ\approx8$ MeV was however detected. The $γ$-ray strength functions measured for Cd isotopes exhibit both features over the range of isotopes, with the low-energy enhancement decreasing- and PDR strength increasing as a function of neutron number. This suggests a transitional region for the onset of low-energy enhancement, and also that the PDR strength depends on the number of neutrons. The $γ$-ray strength functions of $^{105-108}$Pd have been measured in order to further explore the proposed transitional region. Experimental data were obtained at the Oslo Cyclotron Laboratory by using the charged particle reactions ($^{3}$He, $^{3}$He$^{\prime}γ$) and ($^{3}$He, $α$$γ$) on $^{106,108}$Pd target foils. Particle$-γ$ coincidence measurements provided information on initial excitation energies and the corresponding $γ$-ray spectra, which were used to extract the level densities and $γ$-ray strength functions according to the Oslo method. The $γ$-ray strength functions indicate a sudden increase in magnitude for $E_γ>4$ MeV, which is interpreted as a PDR centered at $E_γ\approx8$ MeV. An enhanced $γ$-ray strength at low energies is also observed for $^{105}$Pd, which is the lightest isotope measured in this work. Further, the results correspond and agree very well with the observations from the Cd isotopes, and support the suggested transitional region for the onset of low-energy enhancement with decreasing mass number. The neutron number dependency of the PDR strength is also evident.

nucl-ex↗

arXiv2014

Level density and gamma-ray strength function in the odd-odd 238Np

The level density and gamma-ray strength function in the quasi-continuum of 238Np has been measured using the Oslo method. The level density function follows closely the constant-temperature level density formula and reaches 43 million levels per MeV at Sn = 5.488 MeV of excitation energy. The gamma-ray strength function displays a two-humped resonance at low-energy as also seen in previous investigations of Th, Pa and U isotopes. The structure is interpreted as the scissors resonance and has an average centroid of wSR = 2.26(5) MeV and a total strength of BSR = 10.8(12)m2N, which is in excellent agreement with sum-rule estimates. The scissors resonance is shown to have an impact on the 237Np(n; g)238Np cross section.

nucl-ex↗