One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme astrophysical environments. A particularly challenging part of that question is the creation of the so-called p-nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average γ strength function of Mo92. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the Nb91(p,γ)Mo92 reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of Mo92. Based on our results, we conclude that the Mo92 abundance anomaly is not due to the nuclear physics input to astrophysical model calculations.

The Oslo method has been applied to particle-γ coincidences following the Pu239(d,p) reaction to obtain the nuclear level density (NLD) and γ-ray strength function (γSF) of Pu240. The experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a challenge for the Oslo method as it can have a significant impact on the extracted NLD and γSF. We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's function transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code rainier. The resulting γSF shows a pronounced enhancement between 2-4 MeV that is consistent with the location of the low-energy orbital M1 scissors mode.

An enhanced probability for low-energy γ-emission (upbend, Eγ <3 MeV) at high excitation energies has been observed for several light and mediummass nuclei close to the valley of stability. Also the M1 scissors mode seen in deformed nuclei increases the γ-decay probability for low-energy γ-rays (Eγ ≈ 2-3 MeV). These phenomena, if present in neutron-rich nuclei, have the potential to increase radiative neutron-capture rates relevant for the r-process. The experimental and theoretical status of the upbend is discussed, and preliminary calculations of (n,γ) reaction rates for neutronrich, mid-mass nuclei including the scissors mode are shown.

The level density and γ-ray strength function (γSF) of Pu243 have been measured in the quasicontinuum using the Oslo method. Excited states in Pu243 were populated using the Pu242(d,p) reaction. The level density closely follows the constant-temperature level density formula for excitation energies above the pairing gap. The γSF displays a double-humped resonance at low energy as also seen in previous investigations of actinide isotopes. The structure is interpreted as the scissors resonance and has a centroid of ωSR=2.42(5) MeV and a total strength of BSR=10.1(15)μN2, which is in excellent agreement with sum-rule estimates. The measured level density and γSF were used to calculate the Pu242(n,γ) cross section in a neutron energy range for which there were previously no measured data.

This paper was published online on 29 January 2016 with an error in the author list. The ninth author's name should read as "F. L. Bello Garrote." The author's name has been corrected as of 5 September 2019. The author's name is incorrect in the printed version of the journal.

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.

In this paper we present the first systematic analysis of the impact of the populated vs. intrinsic spin distribution on the nuclear level density and γ-ray strength function retrieved through the Oslo Method. We illustrate the effect of the spin distribution on the recently performed239Pu(d,pγ)240Pu experiment using a 12 MeV deuteron beam performed at the Oslo Cyclotron Lab. In the analysis we couple state-of-the-art calculations for the populated spin-distributions with the Monte-Carlo nuclear decay code RAINIER to compare Oslo Method results to the known input. We find that good knowledge of the populated spin distribution is crucial and show that the populated distribution has a significant impact on the extracted nuclear level density and γ-ray strength function for the239Pu(d,pγ)240Pu case.