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Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL's CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.

The Na23(α,p)Mg26 and Na23(α,n)Al26 reactions are important for our understanding of the Al26 abundance in massive stars. The aim of this work is to report on a direct and simultaneous measurement of these astrophysically important reactions using an active target system. The reactions were investigated in inverse kinematics using He4 as the active target gas in the detector. We measured the excitation functions in the energy range of about 2 to 6 MeV in the center of mass. We have found that the cross sections of the Na23(α,p)Mg26 and the Na23(α,n)Al26 reactions are in good agreement with previous experiments and with statistical-model calculations. The astrophysical reaction rate of the Na23(α,n)Al26 reaction has been reevaluated and it was found to be larger than the recommended rate.

The octupole strength present in the neutron-rich, radiocative nucleus 146Ba has been experimentally determined for the first time using Coulomb excitation. To achieve this, A=146 fission fragments from CARIBU were post-accelerated by the Argonne Tandem Linac Accelerator System (ATLAS) and impinged on a thin 208Pb target. Using the GRETINA γ-ray spectrometer and the CHICO2 heavy-ion counter, the reduced transition probability B(E3; 3-→0+) was determined as 48(+21-29) W.u. The new result provides further experimental evidence for the presence of a region of octupole deformation surrounding the neutron-rich barium isotopes.

Fusion evaporation cross sections for the Al27+Sc45 (Q=9.63 MeV) system are measured down to about 300 nb. Deviations from standard coupled-channels calculations were observed in this system at the lowest energies. The steep fall-off of the fusion cross sections can be reproduced by calculations using a shallow potential model, which was originally developed to explain the hindrance behavior of heavy-ion fusion in medium-mass systems with negative Q values. Comparisons of the hindrance behavior between the present experiment and other systems, for example, Si28+Si30 (Q=14.3 MeV) and S36+Ca48 (Q=7.55 MeV) are presented. © 2010 The American Physical Society. Fil: Jiang, C. L.. Argonne National Laboratory; Estados Unidos Fil: Rehm, K. E.. Argonne National Laboratory; Estados Unidos Fil: Esbensen, H.. Argonne National Laboratory; Estados Unidos Fil: Back, B. B.. Argonne National Laboratory; Estados Unidos Fil: Janssens, R. V. F.. Argonne National Laboratory; Estados Unidos Fil: Collon, P.. University of Notre Dame; Estados Unidos Fil: Deibel, C. M.. Michigan State University; Estados Unidos. Argonne National Laboratory; Estados Unidos Fil: Digiovine, B.. Argonne National Laboratory; Estados Unidos Fil: Figueira, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Argonne National Laboratory; Estados Unidos. Laboratorio Tandar; Argentina Fil: Greene, J. P.. Argonne National Laboratory; Estados Unidos Fil: Henderson, D. J.. Argonne National Laboratory; Estados Unidos Fil: Lee, H. Y.. Los Alamos National Laboratory; Estados Unidos. Argonne National Laboratory; Estados Unidos Fil: Notani, M.. University of Notre Dame; Estados Unidos Fil: Marley, S. T.. Argonne National Laboratory; Estados Unidos. Western Michigan University; Estados Unidos Fil: Pardo, R. C.. Argonne National Laboratory; Estados Unidos Fil: Patel, N.. Argonne National Laboratory; Estados Unidos. Colorado School Of Mines; Estados Unidos Fil: Seweryniak, D.. Argonne National Laboratory; Estados Unidos Fil: Tang, X. D.. University of Notre Dame; Estados Unidos Fil: Ugalde, C.. Argonne National Laboratory; Estados Unidos Fil: Zhu, S.. Argonne National Laboratory; Estados Unidos

A measurement of the β-delayed α decay of N16 using a set of twin ionization chambers is described. Sources were made by implantation, using a N16 beam produced via the In-Flight Technique. The energies and emission angles of the C12 and α particles were measured in coincidence and very clean α spectra, down to energies of 450 keV, were obtained. The structure of the spectra from this experiment is in good agreement with results from previous measurements. An analysis of our data with the same input parameters as used in earlier studies gives SE1(300)=86±22 keVb for the E1 component of the S-factor. This value is in excellent agreement with results obtained from various direct and indirect measurements. In addition, the influence of new measurements including the phase shift data from Tischhauser on the value of SE1(300) is discussed.

An excitation function for the fusion reaction Si28 + Si30 (Q=14.3MeV) has been measured down to 40μb. Deviations from the behavior predicted by the optical model and standard coupled-channels calculations have been observed in this system. The fusion cross sections can be reproduced by a shallow potential model well, which was originally developed to explain the hindrance of heavy-ion fusion for systems with negative Q-values.

We report on a study of the structure of the unbound nucleus He7 utilizing the proton-removal reaction 2H(8Li,3He)7He. Combining the present results with those of our prior measurements of the neutron-adding reaction 2H(6He,p)7He, a consistent picture emerges for the low-lying excitations in He7. Specifically, the negative-parity sequence of resonances, in order of excitation energies, is consistent with 3/2-,1/2-, and 5/2-. The stable-beam reactions 2H(7Li,t)6Li and 2H(7Li,3He)6He were also measured. The results are compared with the predictions of nuclear structure models, including those of ab initio quantum Monte Carlo calculations.

The combined data of two Coulomb excitation experiments has verified the purely electromagnetic population of the Kπ=4+,6+,8-, and 16+ rotational bands in Hf178 via 2≤ν≤14 K-forbidden transitions, quantifying the breakdown of the K-selection rule with increasing spin in the low-K bands. The γ-, 4+, and 6+ bands were extended, and four new states in a rotational band were tentatively assigned to a previously known Kπ=0+ band. The quasiparticle structure of the 6+ (t12=77 ns) and 8- (t12=4 s) isomer bands were evaluated, showing that the gyromagnetic ratios of the 6+ isomer band are consistent with a pure π72+[404],π52+[402] structure. The 8- isomer band at 1147 keV and the second 8- band at 1479 keV, thought to be predominantly ν72-[514],ν92+[624] and π92-[514],π72+[404], respectively, are mixed to a degree approaching the strong-mixing limit. Based on measured Kπ=16+ E2 Kπ=0+ matrix elements, it was shown that heavy-ion bombardment could depopulate the 16+ isomer at the ~1% level, although no states were found that would mediate photodeexcitation of the isomer via low-energy x-ray absorption.

A new measurement of the β-delayed α decay of N16 has been performed using a set of high efficiency ionization chambers. Sources were made by implantation of a N16 beam, yielding very clean α spectra down to energies as low as 400 keV. Our data are in good agreement with earlier results. For the S factor SE1, we obtain a value of 74±21keVb. In spite of improvements in the measurement, the error in SE1 remains relatively large because of the correlations among the fit parameters and the uncertainties inherent to the extrapolation.

Coulomb activation of the four quasiparticle Kπ=16+ Hf178 isomer (t1/2=31y) has led to the measurement of a set of Eλ matrix elements coupling the isomer band to the ground band. The present data combined with earlier Hf178 Coulomb excitation data have probed the K components in the wave functions and revealed the onset and saturation of K mixing in low-K bands, whereas the mixing is negligible in the high-K bands. The implications can be applied to other quadrupole-deformed nuclei.

The Ti44(t1/2=59yr) nuclide, an important signature of supernova nucleosynthesis, has recently been observed as live radioactivity by γ-ray astronomy from the Cas A remnant. We investigate in the laboratory the major Ti44 production reaction Ca40(α,γ)Ti44 (Ec.m.∼0.6-1.2MeV/u) by direct off-line counting of Ti44 nuclei. The yield, significantly higher than inferred from previous experiments, is analyzed in terms of a statistical model using microscopic nuclear inputs. The associated stellar rate has important astrophysical consequences, increasing the calculated supernova Ti44 yield by a factor ∼2 over previous estimates and bringing it closer to Cas A observations.

We have studied the 2H(8Li, p)9Li reaction to obtain information on the spins, parities, and single-neutron spectroscopic factors for states in 9Li, using a radioactive 8Li beam. The deduced properties of the lowest three states are compared to the predictions of a number of calculations for the structure of 9Li. The results of ab initio quantum Monte Carlo calculations are in good agreement with the observed properties.

We have studied the properties of low-lying levels in He7 using the H2(He6,p)He7 reaction at 11.5 MeV/u. This reaction probes the He6g.s.+n character of states in He7. The ground state was populated with a spectroscopic factor comparable to that obtained from ab initio calculations, supporting the tentative spin-parity assignment of 3/2- in the literature. In addition to the ground state, a broad structure is observed between EX=2-3 MeV, the excitation-energy range expected for the 1/2- state in He7. No evidence was found for a lower-lying, first-excited state reported recently.

The fusion excitation function for 64Ni + 64Ni down to a cross section level of 10 nb and have observed a strong fusion hindrance at extreme sub-barrier energies. The onset of the sub-barrier fusion hindrance in 64Ni + 64Ni was found to occur 8.4 MeV lower in center-of-mass energy, whereas a 2 MeV higher energy was expected on the basis of systematics. The effect was found to appear to be associated with the nuclear structure of the interacting nuclei. A strong dependence of the energy where the hindrance was also found to occur on the stiffness of the interacting nuclei.

Large angle elastic scattering of alpha particles from 44Ti, which is the lightest unstable alpha-particle nucleus above A=40, was measured at backward angles. The angular distributions of elastic scattering of alpha particles from 40 and 44Ti were compared. Results indicated that for 40Ca, at angles close to 180° elastic cross sections higher than Rutherford values were confirmed, while corresponding yields for 44Ti were about a factor 20 smaller. An optical model analysis of α+44Ti data produced parameters which were in good agreement with the results.

The astrophysically important reaction 14O(α,p)17F has been studied through a measurement of the time-inverse p(17F,α)14O reaction using a radioactive 17F beam. Resonance parameters for several states above an excitation energy of 7 MeV in 18Ne have been obtained. Through a measurement of the partial widths for elastic and inelastic proton scattering, it was determined that for these resonances the contribution of the 14O(α,p)17F* branch populating the first excited state in 17F is small. The results indicate that the contribution of resonances above Ex=7 MeV to the astrophysical (α,p) reaction rate is smaller than was previously assumed.

Cross sections for the 44Ti(α, p)47V reaction which significantly affects the yield of 44Ti in supernovae were measured in the energy range 5.7MeV ≤ Ec.m. ≤ 9 MeV, using a beam of radioactive 44Ti. The cross sections and the deduced astrophysical reaction rates are larger than the results from theoretical calculations by about a factor of 2. The implications of this increase in the reaction rate for the search of supernovae using space-based gamma detectors are discussed.