The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116;120;124 Sn below the neutron separation energy by means of three independent experimental methods. The γ-ray strength functions (GSFs) extracted from primary γ-decay spectra following charged-particle reactions with the Oslo method and with the shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance.

Nuclei in the 135 I region have been identified as being a possible bottleneck for the i process. Here we present an indirect measurement for the Maxwellian-averaged cross section of 126 Sb(n, γ ). The nuclear level density and the γ -ray strength function of 127 Sb have been extracted from 124 Sn(α, pγ ) 127 Sb data using the Oslo method. The level density in the low-excitation-energy region agrees well with known discrete levels, and the higherexcitation-energy region follows an exponential curve compatible with the constant-temperature model. The strength function between E γ ≈ 1.5-8.0 MeV presents several features, such as an upbend and a possibly doublepeaked pygmy-like structure. None of the theoretical models included in the nuclear reaction code TALYS seem to reproduce the experimental data. The Maxwellian-averaged cross section for the 126 Sb(n, γ ) 127 Sb reaction has been experimentally constrained by using our level-density and strength-function data as input to TALYS. We observe a good agreement with the JINA REACLIB, TENDL, and BRUSLIB libraries, while the ENDF/B-VIII.0 library predicts a significantly higher rate than our results.

The experimental γ -ray strength functions (γ SFs) of 142,[144][145][146][147][148][149][150][151] Nd have been studied for γ -ray energies up to the neutron separation energy using the Oslo method. The results represent a unique set of γ SFs for an isotopic chain with increasing nuclear deformation. The data reveal how the low-energy enhancement, the scissors mode, and the pygmy dipole resonance evolve with nuclear deformation and mass number. This indicates that the mechanisms behind the low-energy enhancement and the scissors mode are decoupled from each other.

Nuclear level densities (NLDs) and γ -ray strength functions (GSFs) of 120,124 Sn have been extracted with the Oslo method from proton-γ coincidences in the (p, p γ ) reaction. The functional forms of the GSFs and NLDs have been further constrained with the Shape method by studying primary γ -transitions to the ground and first excited states. The NLDs demonstrate good agreement with the NLDs of 116,118,122 Sn isotopes measured previously. Moreover, the extracted partial NLD of 1 − levels in 124 Sn is shown to be in fair agreement with those deduced from spectra of relativistic Coulomb excitation in forward-angle inelastic proton scattering. The experimental NLDs have been applied to estimate the magnitude of the Porter-Thomas (PT) fluctuations. Within the PT fluctuations, we conclude that the GSFs for both isotopes can be considered to be independent of initial and final excitation energies, in accordance with the generalized Brink-Axel hypothesis. Particularly large fluctuations observed in the Shape-method GSFs present a considerable contribution to the uncertainty of the method and may be one of the reasons for deviations from the Oslo-method strength at low γ -ray energies and low values of the NLD (below ≈1 × 10 3 -2 × 10 3 MeV −1 ).

Sensitivity studies of the i process have identified the region around 135I as a bottleneck for the neutron capture flow. Nuclear properties such as the Maxwellian-averaged cross section (MACS) are key to constrain the uncertainties in the final abundance patterns. From the 124Sn(α, pγ)127Sb reaction we are able to indirectly measure the nuclear level density and γ-ray strength function for 127Sb using the Oslo method. From these two quantities we can calculate the MACS for the 126Sb(n, γ)127Sb reaction using the Hauser-Feshbach formalism, constrain its uncertainties and compare it to libraries such as JINA REACLIB, TENDL and BRUSLIB.