Measurements consisting of γ-ray excitation functions and angular distributions have been performed using the (n, n ′ γ) reaction on 62 Ni. The excitation function data allowed us to check the consistency of the placement of transitions in the level scheme. From γ-ray angular distributions, the lifetimes of levels up to ∼ 3.8 MeV in excitation energy have been extracted with the Doppler-shift attenuation method. The experimentally deduced values of reduced transition probabilities have been compared with the predictions of the quadrupole vibrator model and with large-scale shell model calculations in the f p shell configuration space. Two-phonon states have been found to exist with some notable deviation from the predictions of the quadrupole vibrator model, but no evidence for the existence of three-phonon states could be established. Z = 28 proton core excitations play a major role in understanding the observed structure.

Background: Astrophysical models studying the origin of the neutron-deficient p nuclides require the knowledge of proton capture cross sections at low energy. The production site of the p nuclei is still under discussion but a firm basis of nuclear reaction rates is required to address the astrophysical uncertainties. Data at astrophysically relevant interaction energies are scarce. Problems with the prediction of charged particle capture cross sections at low energy were found in the comparisons between previous data and calculations in the Hauser-Feshbach statistical model of compound reactions.Purpose: A measurement of 74 Ge(p,γ) 75 As at low proton energies, inside the astrophysically relevant energy region, is important in several respects. The reaction is directly important as it is a bottleneck in the reaction flow which produces the lightest p nucleus 74 Se. It is also an important addition to the data set required to test reaction-rate predictions and to allow an improvement in the global p+nucleus optical potential required in such calculations.Method: An in-beam experiment was performed, making it possible to measure in the range 2.1 ≤ Ep ≤ 3.7 MeV, which is for the most part inside the astrophysically relevant energy window. Angular distributions of the γ-ray transitions were measured with high-purity germanium detectors at eight angles relative to the beam axis. In addition to the total cross sections, partial cross sections for the direct population of twelve levels were determined. Results:The resulting cross sections were compared to Hauser-Feshbach calculations using the code SMARAGD. Only a constant renormalization factor of the calculated proton widths allowed a good reproduction of both total and partial cross sections. The accuracy of the calculation made it possible to check the spin assignment of some states in 75 As. In the case of the 1075 keV state, a double state with spins and parities of 3/2 − and 5/2 − is needed to explain the experimental partial cross sections. A change in parity from 5/2 + to 5/2 − is required for the state at 401 keV. Furthermore, in the case of 74 Ge, studying the combination of total and partial cross sections made it possible to test the γ width, which is essential in the calculation of the astrophysical 74 As(n,γ) 75 As rate. Conclusions:Between data and statistical model prediction a factor of about two was found. Nevertheless, the improved astrophysical reaction rate of 74 Ge(p,γ) (and its reverse reaction) is only 28% larger than the previous standard rate. The prediction of the 74 As(n,γ) 75 As rate (and its reverse) was confirmed, the newly calculated rate differs only by a few percent from the previous prediction. The in-beam method with high efficiency detectors proved to be a powerful tool for studies in nuclear astrophysics and nuclear structure.

Inelastic neutron scattering was used to study the low-lying nuclear structure of 132 Xe. A comprehensive level scheme is presented, as well as new level lifetimes, multipole mixing ratios, branching ratios, and transition probabilities. Comparisons of these data as well as previously measured E2 strengths and g factors are made with new shell-model calculations for 132,134,136 Xe to explore the emergence of collectivity in the Xe isotopes with N < 82 near the closed shell. *

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a b s t r a c tIn this study, we have sought to determine the advantages, disadvantages, and viability of open cycle thorium-uranium-fuelled (Th-U-fuelled) nuclear energy systems. This has been done by assessing three such systems, each of which requires uranium enriched to $20% 235 U, in comparison to a reference uranium-fuelled (U-fuelled) system over various performance indicators, spanning material flows, waste composition, economics, and proliferation resistance. The values of these indicators were determined using the UK National Nuclear Laboratory's fuel cycle modelling code ORION. This code required the results of lattice-physics calculations to model the neutronics of each nuclear energy system, and these were obtained using various nuclear reactor physics codes and burn-up routines. In summary, all three Th-U-fuelled nuclear energy systems required more separative work capacity than the equivalent benchmark U-fuelled system, with larger levelised fuel cycle costs and larger levelised cost of electricity. Although a reduction of $6% in the required uranium ore per kWh was seen for one of the Th-U-fuelled systems compared to the reference U-fuelled system, the other two Th-U-fuelled systems required more uranium ore per kWh than the reference. Negligible advantages and disadvantages were observed for the amount and the properties of the spent nuclear fuel (SNF) generated by the systems considered. Two of the Th-U-fuelled systems showed some benefit in terms of proliferation resistance of the SNF generated.Overall, it appears that there is little merit in incorporating thorium into nuclear energy systems operating with open nuclear fuel cycles.

The level structure of 134 Xe was studied with the inelastic neutron scattering reaction followed by γ-ray detection. A number of level lifetimes were determined for the first time with the Doppler-shift attenuation method and the low-lying excited states were characterized. From this new spectroscopic information, the third excited state, a 0 + level which had only been observed in a previous inelastic neutron scattering study, was verified. Reduced transition probabilities were calculated; comparisons were drawn with a vibrational description of the nucleus and found lacking. The 3 − octupole phonon has been confirmed, and the complete negative-parity multiplet resulting from the ν(1h 11/2 2d 3/2 ) configuration has also been tentatively identified for the first time in the N = 80 isotones.

The low-lying, low-spin levels of 76 Ge were studied with the (n,n ′ γ) reaction. Gamma-ray excitation function measurements were performed at incident neutron energies from 1.6 to 3.7 MeV, and γ-ray angular distributions were measured at neutron energies of 3.0 and 3.5 MeV. From these measurements, level spins, level lifetimes, γ-ray intensities, and multipole mixing ratios were determined. No evidence for a number of previously placed levels was found. Below 3.3 MeV, many new levels were identified, and the level scheme was re-evaluated. The B(E2) values support low-lying band structure. The 2 + mixed-symmetry state has been identified for the first time. A comparison of the level characteristics with large-scale shell model calculations yielded excellent agreement.

The yrast sequence of the neutron-rich dysprosium isotope 168 Dy has been studied using multinucleon transfer reactions following collisions between a 460-MeV 82 Se beam and an 170 Er target. The reaction products were identified using the PRISMA magnetic spectrometer and the γ rays detected using the CLARA HPGe-detector array. The 2 + and 4 + members of the previously measured ground-state rotational band of 168 Dy have been confirmed and the yrast band extended up to 10 + . A tentative candidate for the 4 + → 2 + transition in 170 Dy was also identified. The data on these nuclei and on the lighter even-even dysprosium isotopes are interpreted in terms of total Routhian surface calculations and the evolution of collectivity in the vicinity of the proton-neutron valence product maximum is discussed.