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Proton-$\gamma$ coincidences from $(\mathrm{d},\mathrm{p})$ reactions between a $^{66}\mathrm{Ni}$ beam and a deuterated polyethylene target have been analyzed with the inverse Oslo method to find the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF) of $^{67}\mathrm{Ni}$. The $^{66}\mathrm{Ni}(\mathrm{n},\gamma)$ capture cross section has been calculated using the Hauser-Feshbach model in TALYS using the measured NLD and $\gamma$SF as constraints. We confirm that $^{66}\mathrm{Ni}(\mathrm{n},\gamma)$ acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, we find that the impact of this reaction is strongly damped in multi-zone low-metallicity AGB stellar models experiencing i-process nucleosynthesis., Comment: Submitted to Phys. Rev. C

A novel technique for extracting the gamma-ray strength function (SF) and nuclear level density (NLD) from inverse kinematics experiments is presented, which allows for measurements of these properties, across a vast range of previously inaccessible nuclei. Proton-gamma coincidence events from the d(86Kr, p)87Kr reaction were measured at iThemba LABS and the SF and NLD in 87 Kr obtained with the Oslo Method.The SF and NLD are important parameters in Hauser-Feshbach calculations to constrain (n,gamma) cross sections of nuclei for which these cannot be measured directly. The extracted SF and NLD are used as input in Hauser-Feshbach calculations to constrain the 86Kr(n,gamma)87Kr cross section which is important for the 87Rb production in the s-process. The nature of the low-energy region of the SF is explored through comparison to shell model calculations with the LNPS-SDG interaction.

We have recently successfully demonstrated a new technique for production and study of many of the most exotic neutron-rich nuclei at moderate spins. LICORNE, a newly developed directional inverse-kinematic fast neutron source at the IPN Orsay, was coupled to the MINIBALL high resolution gamma-ray spectrometer to study nuclei the furthest from stability using the U-238 (n, f) reaction. This reaction and Th-232 (n, f) are the most neutron-rich fission production mechanisms achievable and can be used to simultaneously populate hundreds of neutron-rich nuclei up to spins of approximate to 16 h. High selectivity in the experiment was achieved via triple gamma-ray coincidences and the use of a 400 ns period pulsed neutron beam, a technique which is unavailable to other population mechanisms such as U-235 (n(th), f) and Cf-252(SF). The pulsing allows time correlations to be exploited to separate delayed gamma rays from isomeric states in the hundreds of nuclei produced, which are then used to cleanly select a particular nucleus and its exotic binary partners. In the recent experiment, several physics cases are simultaneously addressed such as shape coexistence, the evolution of shell closures far from stability, and the spectroscopy of nuclei in the r-process path near N = 82. Preliminary physics results on anomalies in the U-238 (n, f) fission yields and the structure of the Te-138 and Sr-100 nuclei will soon be published. A future project, nu-ball, to couple LICORNE with a hybrid escape-suppressed spectrometer to refine further the technique and achieve a large increase in the observational limit is discussed.

Fast-neutron-induced fission of U-238 at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency.-ray spectrometer (MINIBALL) to an inversekinematics neutron source (LICORNE) to extract charge yields of fission fragments via gamma-gamma coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fastneutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly.

We have recently successfully demonstrated a new technique for production and study of many of the most exotic neutron-rich nuclei at moderate spins. LICORNE, a newly developed directional inverse-kinematic fast neutron source at the IPN Orsay, was coupled to the MINIBALL high resolution gamma-ray spectrometer to study nuclei the furthest from stability using the U-238 (n, f) reaction. This reaction and Th-232 (n, f) are the most neutron-rich fission production mechanisms achievable and can be used to simultaneously populate hundreds of neutron-rich nuclei up to spins of approximate to 16 h. High selectivity in the experiment was achieved via triple gamma-ray coincidences and the use of a 400 ns period pulsed neutron beam, a technique which is unavailable to other population mechanisms such as U-235 (n(th), f) and Cf-252(SF). The pulsing allows time correlations to be exploited to separate delayed gamma rays from isomeric states in the hundreds of nuclei produced, which are then used to cleanly select a particular nucleus and its exotic binary partners. In the recent experiment, several physics cases are simultaneously addressed such as shape coexistence, the evolution of shell closures far from stability, and the spectroscopy of nuclei in the r-process path near N = 82. Preliminary physics results on anomalies in the U-238 (n, f) fission yields and the structure of the Te-138 and Sr-100 nuclei will soon be published. A future project, nu-ball, to couple LICORNE with a hybrid escape-suppressed spectrometer to refine further the technique and achieve a large increase in the observational limit is discussed.

Fast-neutron-induced fission of U-238 at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency.-ray spectrometer (MINIBALL) to an inversekinematics neutron source (LICORNE) to extract charge yields of fission fragments via gamma-gamma coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fastneutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly.

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 description of the so-called p-nuclei, which are believed to be mainly produced in some types of supernovae. In this work, we present for the first time measurements on the nuclear level density and average strength function of 92 Mo. State-of-the-art p-process calculations systematically underestimate the observed solar abundance. Our data provide stringent constraints on the 91 Nb(p,gamma92 Mo reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of 92 Mo. Based on our results, we conclude that the 92 Mo abundance anomaly is not due to the nuclear physics input.

Isospin properties of dipole states in 74Ge are investigated using the (alpha,alpha') reaction and compared to (gamma,gamma') data. The results indicate that the dipole states in the excitation energy region of 6 to 8 MeV adhere to the scenario of the recently found splitting of the region of dipole states into two separated parts: one at low energy being populated by both isoscalar and isovector probes and the other at high energy excited only by the electromagnetic probe. RQTBA calculations show a reduction in the isoscalar E1 strength with an increase in excitation energy which is consistent with the measurement.

The gamma-ray strength functions and level densities of 73,74Ge have been extracted up to the neutron separation energy Sn from particle- coincidence data using the Oslo method. Moreover, the gamma-ray strength function of 74Ge above Sn has been determined from photo-neutron measurements; hence these two experiments cover the range of E = 1 - 13 MeV for 74 Ge. The obtained data show that both 73,74 Ge display an increase in strength at low energies. The experimental strength functions are compared with M1 strength functions deduced from average B(M1) values calculated within the shell model for a large number of transitions. The observed low-energy enhancements in 73,74 Geare adopted in the calculations of the 72,73Ge(n,gamma) cross sections, where there are no direct experimental data. Reaction rate calculations for more neutron-rich germanium isotopes are shown to be sensitive to a low-energy enhancement.

Forty-six decay chains, assigned to the decay of 288-115, were produced using the 243Am(48Ca,3n)288-115 reaction at the Lawrence Berkeley National Laboratory 88-in. cyclotron. The resulting series of α decays were studied using α-photon and α-x-ray spectroscopies. Multiple α-photon coincidences were observed in the element 115 decay chain members, particularly in the third- and fourth-generation decays (presumed to be 280Rg and 276Mt, respectively). Upon combining these data with those from 22 288-115 decay chains observed in a similar experiment, updated level schemes in 276Mt and 272Bh (populated by the α decay of 280Rg and 276Mt, respectively) are proposed. Photons were observed in the energy range expected for K x rays coincident with the α decay of both 280Rg and 276Mt. However, Compton scattering of higher-energy γ rays and discrete transitions are present in the K x-ray region preventing a definitive Z identification to be made based on observation of characteristic K x-ray energies.

We evaluate two dominant nuclear reaction rates and their uncertainties that affect 44Ti production in explosive nucleosynthesis. Experimentally we develop thick-target yields for the 40Ca(alpha,gamma)44Ti reaction at E(alpha) = 4.13, 4.54, and 5.36 MeV using gamma-ray spectroscopy. At the highest beam energy, we also performed an activation measurement that agrees with the thick target result. From the measured yields a stellar reaction rate was developed that is smaller than current statistical-model calculations and recent experimental results, which would suggest lower 44Ti production in scenarios for the alpha-rich freeze out. Special attention has been paid to assessing realistic uncertainties of stellar rates produced from a combination of experimental and theoretical cross sections, which we use to develop a re-evaluation of the 44Ti(alpha,p)47V reaction rate. Using these we carry out a sensitivity survey of 44Ti synthesis in eight expansions representing peak temperature and density conditions drawn from a suite of recent supernova explosion models. Our results suggest that the current uncertainty in these two reaction rates could lead to as large an uncertainty in 44Ti synthesis as that produced by different treatments of stellar physics., Comment: Comments: 45 pages, 19 postscript figures Minor corrections from Referee and Proof Editors Figs 9 & 10 now in color

We evaluate two dominant nuclear reaction rates and their uncertainties that affect 44Ti production in explosive nucleosynthesis. Experimentally we develop thick-target yields for the 40Ca(alpha,gamma)44Ti reaction at E(alpha) = 4.13, 4.54, and 5.36 MeV using gamma-ray spectroscopy. At the highest beam energy, we also performed an activation measurement that agrees with the thick target result. From the measured yields a stellar reaction rate was developed that is smaller than current statistical-model calculations and recent experimental results, which would suggest lower 44Ti production in scenarios for the alpha-rich freeze out. Special attention has been paid to assessing realistic uncertainties of stellar rates produced from a combination of experimental and theoretical cross sections, which we use to develop a re-evaluation of the 44Ti(alpha,p)47V reaction rate. Using these we carry out a sensitivity survey of 44Ti synthesis in eight expansions representing peak temperature and density conditions drawn from a suite of recent supernova explosion models. Our results suggest that the current uncertainty in these two reaction rates could lead to as large an uncertainty in 44Ti synthesis as that produced by different treatments of stellar physics., Comment: Comments: 45 pages, 19 postscript figures Minor corrections from Referee and Proof Editors Figs 9 & 10 now in color

Excited states in (256)Rf were populated via the Pb-208(Ti-50,2n) fusion-evaporation reaction. Delayed gamma-ray and electron decay spectroscopy was performed and three isomeric states in (256)Rf have been identified. A fourth low-energy nonyrast state was identified from the gamma-ray decay of one of the higher lying isomers. The states are interpreted as multi-quasiparticle excitations., QC 20100525