Search

Carbon and oxygen burning reactions, in particular, $^{12}\mathrm{C}+^{12}\mathrm{C}$ fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\ensuremath{\gamma}$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for $^{12}\mathrm{C}+^{12}\mathrm{C}$ fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

Carbon and oxygen burning reactions, in particular, $^{12}$C+$^{12}$C fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\gamma$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for $^{12}$C+$^{12}$C fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed., Comment: accepted for publication in Phys. Rev. Lett

The elastic scattering of the radioactive proton-rich carbon isotope $^{10}\mathrm{C}$ has been investigated. A full differential angular distribution for the elastic scattering of $^{10}\mathrm{C}$ on a $^{58}\mathrm{Ni}$ target has been measured at ${E}_{\mathrm{Lab}}=35.3$ MeV, which is just above the Coulomb barrier for this system (${V}_{B}=27$ MeV). The obtained angular distribution was analyzed in terms of coupled-channels, coupled-reaction-channels, and continuum-discretized coupled-channels calculations. In the coupled-channels calculation, several inelastic transitions of the target and the first (${2}^{+}$) excited state of the $^{10}\mathrm{C}$ projectile were considered. The coupling to the first (${2}^{+}$) excited state of $^{10}\mathrm{C}$ was shown to be very important to describe the rising of the cross section at backward angles. We also performed an analysis with the continuum-discretized coupled channels, considering the $^{9}\mathrm{B}+p$ and $^{6}\mathrm{Be}+\ensuremath{\alpha}$ channels, which indicated a strong cluster configuration for the $^{10}\mathrm{C}$ projectile.

Nuclear Reactions around the Coulomb barrier are complex in nature due to the existence of non-fusion channels at these energies, and offers excellent opportunities to explore several dynamical effects as well as the sub-lime effects of nuclear structure. Some of the outstanding issues related to nuclear reactions at these energies are: the role of nucleon transfer events in the manipulation of fusion cross-section, and pairing correlations. As such, an experiment was performed to carry out some conclusive measurements for the 10B+27Al system at energies ≈ 1.3 - 1.7 MeV/A. The experiment based on γ-ray spectroscopy has been performed at the Tandem Laboratory, National Institute of Nuclear Investigation, Mexico, to obtain the fusion cross-sections at several beam energies. In the present paper, some experimental details, analysis and preliminary results are presented.

Evaporation-proton yields were measured for the fusion of the weakly bound nucleus $^{6}\mathrm{Li}$ on a $^{58}\mathrm{Ni}$ target at six near- or sub-barrier bombarding energies. Effects of the one-neutron transfer reaction were estimated and corrections made. Total-fusion cross sections were deduced using calculated proton multiplicities. The resulting fusion excitation function shows a considerable enhancement with respect to calculations for a bare potential. Inelastic couplings are estimated to have insignificant effects on such fusion. The sum of total fusion plus one-neutron transfer cross sections nearly saturates the total reaction cross section in the energy region measured. Comparison with previous results appropriately scaled for the $^{6}\mathrm{Li}+(^{59}\mathrm{Co}, ^{64}\mathrm{Ni}, ^{64}\mathrm{Zn})$ systems shows good consistency except for some data spread at the lower energies.

We present $^{8}\mathrm{B}+^{27}\mathrm{Al}$ elastic scattering angular distributions for the proton-halo nucleus $^{8}\mathrm{B}$ at two energies above the Coulomb barrier, namely ${E}_{\mathrm{lab}}=15.3$ and 21.7 MeV. The experiments were performed in the Radioactive Ion Beams in Brasil facility (RIBRAS) in S\~ao Paulo, and in the TwinSol facility at the University of Notre Dame, USA. The angular distributions were measured in the angular range of 15--80 degrees. Optical model and continuum discretized coupled channels calculations were performed, and the total reaction cross sections were derived. A comparison of the $^{8}\mathrm{B}+^{27}\mathrm{Al}$ total reaction cross sections with similar systems including exotic, weakly bound, and tightly bound projectiles impinging on the same target is presented.

Previously reported data for fusion of the $^{8}\mathrm{B}+(^{58}\mathrm{Ni},^{28}\mathrm{Si})$ systems are critically reviewed. New $\ensuremath{\alpha}\text{-particle}$ data from the fusion of $^{8}\mathrm{B}+^{58}\mathrm{Ni}$ also are reported, but the paper is mostly based on using realistic calculations of well-established codes to reanalyze the previous data. The influence of breakup protons on the evaporation proton measurements for the heavier system is found to be small at all energies except for the lowest one measured, and corrections are made for this process. Possible model dependencies in the deduced fusion cross sections are investigated using three different evaporation codes. The data sets for the $^{58}\mathrm{Ni}$ and $^{28}\mathrm{Si}$ targets are shown to be consistent with each other and with fusion enhancement up to energies that are greater than the Coulomb barrier ${V}_{b}$ $({E}_{\text{c.m.}}\ensuremath{\lesssim}\phantom{\rule{4pt}{0ex}}{\mathrm{V}}_{b}+1.5\ifmmode\times\else\texttimes\fi{}\ensuremath{\hbar}\ensuremath{\omega})$. This limit corresponds to 6.2 MeV above the barrier for the $^{58}\mathrm{Ni}$ target. An important difference with the behavior of neutron-halo systems is thus confirmed.

Elastic scattering angular distributions for the 9Be+51V system were measured at three near Coulomb barrier energies, Elab = 16.35, 17.44 and 18.53 MeV. The data were analyzed by using a Semimicroscopic Optical Model. This combines a microscopic calculation of the mean-field double folding potential and a phenomenological construction of the dynamical polarization potential. The calculations reproduced the data very well and the total reaction cross sections were also calculated.

The 12 C + 12 C fusion reaction has been studied in the center-of-mass energy range of 2.25 to 6.01 MeV. Through the detection of gamma rays from the first excited states of the residual nuclei 20 Ne, 23 Na and 23 Mg, absolute cross sections for the 12 C( 12 C, α ), 12 C( 12 C, p) and 12 C( 12 C, n) reactions have been obtained. In this new measurement, the energy dependence of the S -factor is found to increase as the energy decreases below 3 MeV in the center of mass. This tendency was observed in previous measurements by Mazarakis et al., and has since then become a subject of controversy. In this work, where the cross sections are measured at even lower energies, we confirm the rise in the S -factor toward the energy region relevant for star evolution and nucleosynthesis calculations ( E c . m . = 1 – 3 MeV ).

The RBS technique is applied to solve the problem of on-line monitoring of the carbon deposited on a thin backed foil under ion bombardment. An iterative method is used to reliably extract quantities such as number of projectiles and target thickness in spite of beam energy changes and detector unstabilities. Experimental values for secondary electron yields are also deduced. Results are reported for the thickness variation of thin carbon foils bombarded with carbon ions of energies between 8.95 and 13 MeV. A linear correlation of this variation is found with both, the ion fluence at target and the number of secondary electrons emitted. The correlation exists even though a wide range of beam currents, beam energies and bombarding times was used during the experiment. The measured electron yields show evidence for a change in the emission process between the original foils and the deposited layer, possibly due to a texture change.

By using some simple model assumptions, the relative contribution of collective and transfer degrees of freedom to the sub-barrier fusion of several systems is investigated. Previously measured data for 32S + 58,64Ni, 37Cl + 58,60,62,64Ni, 37Cl + 70,72,73,74,76Ge, and 27Al + 70,72,73,74,76Ge are analyzed. Even though the effects of collective degrees of freedom are dominant, transfer effects are shown to be important for many systems in order to account for the trend of the lower energy points. Under simplified assumptions for the transfer strength, a distance for transfer is estimated for some systems. An apparent inconsistency found in previous analysis of the Cl + Ge data is solved.

Recently, experimental measurements of elastic scattering angular distributions for the system7Li+58Ni at ten different energies around the Coulomb barrier were made by the Heavy-Ion Group. The measurements were made at the Tandem Van de Graaff Particle Accelerator Laboratory in the National Institute for Nuclear Research (ININ) in Mexico. In this work, preliminary elastic scattering angular distributions for five energies (E lab , = 12.0, 12.5, 13.0, 13.5 and 14.22 MeV) are presented. The preliminary experimental data were analyzed using the Sao Paulo Optical Model Potential (SPP) which is based on a double-folding potential, reproducing very well these data. A comparison is made with old data reported back in 1973 and in 2012. Further analysis is in progress in order to fully understand this particular system, specially because7Li is known to be a weakly bound nucleus.

Preliminary results for the elastic scattering of the Super-Borromean nucleus10C on27Al are presented, at E lab = 29 MeV. Taking the Sao Paulo potential as the bare potential, possible polarization potentials are investigated by adding a volume and a surface complex term to account for fusion and direct couplings, respectively. Besides an imaginary short-range potential to simulate the bulk of fusion, the best-fit polarization potential turns out to be real and has the effect of shifting the barrier radius up by 0.6 fm, thus suggesting a fusion enhancement.

Elastic scattering angular distributions of the radioactive weakly bound $^{7}\mathrm{Be}$ on $^{27}\mathrm{Al}$ have been measured at energies near the Coulomb barrier. The interaction optical potential is investigated by using different potentials. Total reaction cross sections have also been obtained.

We have performed continuum-discretized coupled channels (CDCC) calculations of the breakup of 8 B on 58 Ni in the energy interval 10 - 26 MeV in the c.m. system. Elastic scattering angular distributions for the 8 B + 58 Ni system at five different energies around the Coulomb barrier were studied by using the CDCC model and taking into account a coupling between elastic and breakup channels. The energy-dependent sets found for the OPs parameters reproduce well the elastic scattering data and the fusion and reaction cross sections. Finally, a comparison of the reduced total reaction cross sections for the 8 B + 58 Ni system with the 6 He + 208 Pb and 6 He + 209 Bi systems is presented.

The fusion of ${}^{6}\mathrm{He}$ with a ${}^{209}\mathrm{Bi}$ target has been studied at energies near to and below the Coulomb barrier. Despite the weak binding of the valence neutrons in ${}^{6}\mathrm{He}$, little evidence is found for suppression of fusion due to projectile breakup. Instead, a large enhancement of sub-barrier fusion is observed. It is suggested that this enhancement may arise from coupling to positive $Q$ value neutron transfer channels, resulting in ``neutron flow'' between the projectile and the target.

Fission following the fusion of {sup 6}He with a {sup 209}Bi target has been studied near the Coulomb barrier, at excitation energies of 32 and 34 MeV in the compound system. These new experimental data are in disagreement with previous work which reported an anomalously large fusion-fission yield, when compared with {sup 4}He-induced fission of {sup 209}Bi at similar excitation energies. In fact, the {sup 6}He-induced fusion-fission yield appears to be smaller than that for {sup 4}He, in qualitative agreement with conventional statistical model calculations. {copyright} {ital 1998} {ital The American Physical Society}

Acrylonitrile content from copolymer of acrylonitrile-butadiene has been studied combining vibrational spectroscopy and a nuclear technique. On the basis of the results obtained, it has been proven that these techniques can clearly be an asset to determine acrylonitrile content in rubber materials without prior separation and in a nondestructive fast and simple manner. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 187–190, 1997

Sub-barrier fusion cross sections (σfus ) for the 6 Li + 58 Ni system, obtained from the respective evaporation protons, are examined in the present work. With respect to expectations of a simple one-dimensional barrier penetration model, a large enhancement of the data is observed. Good consistency with equivalent data reported previously for similar systems is found. A comparison with total reaction cross sections (σR ), deduced from elastic scattering measurements reported previously, indicates that σfus is close to σR within the measured energy range. To estimate the contribution of complete fusion (CF), an optical model analysis of the elastic scattering data is performed where CF is identified with the absorption in a short range volume potential. A surface polarization potential is added to the bare nuclear potential to simulate the effect of peripheral reactions. The results obtained indicate that other mechanisms different from CF may be dominant, especially in the lower energy region.

Calculations of breakup and direct proton transfer for the 8 B+ 58 Ni system at energies around the Coulomb barrier ( E B,lab =22.95 MeV) were performed by the continuum-discretized coupled channels (CDCC) method and the coupled-reaction-channels (CRC) method, respectively. For the 7 Be+ 58 Ni interaction, we used a semimicroscopic optical model potential (OMP) that combines microscopic calculations of the mean-field double folding potential and a phenomenological construction of the dynamical polarization potential (DPP). The 7 Be angular distribution at E lab =25.75 MeV from the 8 B breakup on 58 Ni was calculated and the spectroscopic factor for 8 B → 7 Be+ p vertex, S expt = 1.10 ± 0.05, was deduced. The astrophysical S 17 (0) factor was calculated equal to 20.7 ±1.1 eV•b, being in good agreement with the previously reported values.

Evaporation protons from the fusion of the ${}^{3}\mathrm{He}{+}^{58}$Ni system were measured at three energies near but above the Coulomb barrier. The respective elastic scattering angular distribution was also determined for one of these energies. The fusion data, after being properly reduced to eliminate size and charge effects, are compared to the recently measured fusion excitation function for the proton-halo system ${}^{8}\mathrm{B}{+}^{58}$Ni. As a reference, fusion data for the ${}^{16}\mathrm{O}{+}^{58}$Ni system are also presented. With respect to this reference, the fusion cross sections for the proton-rich systems show an enhancement likely related to static effects. An excitation function for the respective total-reaction cross section was extracted from the measured elastic data along with additional data from the literature. Surprisingly, this excitation function follows the trend expected for weakly bound systems.

Fusion cross sections were measured for the exotic proton-halo nucleus {sup 8}B incident on a {sup 58}Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a proton-halo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section.

Fusion cross sections were measured for the exotic proton-halo nucleus ⁸B incident on a ⁵⁸Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a proton-halo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section.

We have performed continuum-discretized coupled channels (CDCC) calculations of the breakup of $^{8}\mathrm{B}$ on $^{58}\mathrm{Ni}$ and direct proton transfer for the $^{8}\mathrm{B}+^{58}\mathrm{Ni}$ system at laboratory energies of $20--28.4$ MeV. The influence of the $^{7}\mathrm{Be}$ core-target optical potential (OP) on the breakup cross section was investigated. Elastic scattering angular distributions for the $^{7}\mathrm{Be}+^{58}\mathrm{Ni}$ and $^{8}\mathrm{B}+^{58}\mathrm{Ni}$ systems at five different energies around the Coulomb barrier were studied, and a reasonable energy-independent OP for each system was obtained. Using these OPs and two different $^{7}\mathrm{Be}$-$p$ relative motion wave functions, and summing breakup and direct proton transfer contributions, we were able to fit the experimental cross section at a $^{8}\mathrm{B}$ laboratory energy of $25.75$ MeV. We calculated the excitation function for the $^{7}\mathrm{Be}$ emission in the $^{8}\mathrm{B}+^{58}\mathrm{Ni}$ reaction, where $^{7}\mathrm{Be}$ products were measured at the forward angle ${\ensuremath{\theta}}_{\mathrm{lab}}={45}^{\ifmmode^\circ\else\textdegree\fi{}}$ in the energy interval ${E}_{\mathrm{lab}}=20--28.4$ MeV. In view of the peripheral character of the $^{8}\mathrm{B}$ breakup reaction at near-barrier energies, we could extract the asymptotic normalization coefficient for the $^{7}\mathrm{Be}$-$p$ system, which was found to be ${C}_{\mathrm{Be}--p,{p}_{3/2}}^{2}=0.543\ifmmode\pm\else\textpm\fi{}0.027$ fm${}^{\ensuremath{-}1}$. Finally, the astrophysical ${S}_{17}$(0) factor was found to be ${S}_{17}(0)=20.8\ifmmode\pm\else\textpm\fi{}1.1$ eV b.

The $^{211,212}\mathrm{At}$ yields resulting from the interaction of the radioactive projectile $^{8}\mathrm{Li}$ with a $^{208}\mathrm{Pb}$ target have been measured at energies between $3$ and $8.5$ MeV above the Coulomb barrier. They are signatures for fusion of the whole charge but not necessarily the whole mass of the projectile, so they are included in a corresponding operational definition of complete fusion. Within this definition, a fusion suppression factor of $0.70\ifmmode\pm\else\textpm\fi{}0.02$ (stat.) $\ifmmode\pm\else\textpm\fi{}0.04$ (syst.) is deduced from a comparison to a one-dimensional barrier-penetration-model calculation using parameters extrapolated from values for $^{6,7}\mathrm{Li}+^{209}\mathrm{Bi}$ and $^{9}\mathrm{Be}+^{208}\mathrm{Pb}$ taken from the literature. Possible incomplete fusion processes are discussed and the results are fitted with a phenomenological model assuming breakup prior to fusion followed by capture of a $^{7}\mathrm{Li}$ fragment.

Elastic scattering of $^{8}\mathrm{B}$, $^{7}\mathrm{Be}$, and $^{6}\mathrm{Li}$ on a $^{58}\mathrm{Ni}$ target has been measured at energies near the Coulomb barrier. Optical-model fits were made to the experimental angular distributions, and total reaction cross sections were deduced. A comparison with other systems provides striking evidence for proton-halo effects on $^{8}\mathrm{B}$ reactions. As opposed to the situation for the neutron-halo nucleus $^{6}\mathrm{He}$, for which particle transfer dominates, the ``extra'' cross section observed for $^{8}\mathrm{B}$ appears to result entirely from projectile breakup.

Angular distributions for the ${}^{9}\mathrm{Be}({}^{8}\mathrm{Li},{}^{9}\mathrm{Be}){}^{8}\mathrm{Li}$ elastic-transfer reaction have been measured with a 27-MeV $^{8}\mathrm{Li}$ radioactive nuclear beam. Spectroscopic factors for the $\ensuremath{\langle}{}^{9}\mathrm{Be}|{}^{8}\mathrm{Li}+p\ensuremath{\rangle}$ bound system were obtained from the comparison between the experimental differential cross sections and finite-range distorted-wave Born approximation calculations made with the code FRESCO. The spectroscopic factors so obtained are compared with shell-model calculations and other experimental values. Using the present value for the spectroscopic factors, cross sections and reaction rates for the ${}^{8}\mathrm{Li}(p,\ensuremath{\gamma}){}^{9}\mathrm{Be}$ direct proton-capture reaction of astrophysical interest were calculated in the framework of the potential model.

Allanites from Telixtlahuaca (Oaxaca, Mexico) were analyzed using the PIXE technique. The concentrations of 12 elements, mainly rare earths, were determined.

A parameterization of the spectroscopic factor is presented which almost matches the ones obtained via the microscopic SU(3) model of the nucleus. A short introduction of the algebraic model (the Semimicroscopic Algebraic Cluster Model, SACM) is given. The parameterization of the spectroscopic factor is explained, justified and compared, for light nuclei, to the microscopic SU(3) model. The applications concern the calculation of the total fusion cross section of 12C+12C.

Very recently, fusion cross sections for the weakly-bound proton-rich systems (8B,7Be) + 58Ni were obtained by using a technique where the protons evaporated after the respective fusion reaction were measured. In the present work, the same technique is applied to get fusion cross sections for the 6 Li + 58Ni system at sub-barrier energies. Comparison with data reported previously for 6Li projectiles on similar targets gives consistent results, even though the previous data were obtained with quite different techniques.

Fusion excitation functions are measured for the {alpha},p, and n evaporation channels in the fusion of the {sup 12}C+{sup 12}C system at center-of-mass energies between 4.42 and 6.48 MeV, with energy steps of 75 keV. The {gamma}-ray technique is used with a new absolute normalization method which is independent of charge collection, allowing one to monitor at the same time the carbon buildup at the target. Discrepancies between previous works are discussed and a simple unification is proposed. Barrier penetration model (BPM) calculations are consistent with a belly-to-belly orientation of the oblate deformed {sup 12}C nuclei at the touching point. As in previous works, much structure is seen in the excitation function which is nearly consistent with the positions of resonances reported in the literature for this system. Using BPM predictions for the background excitation function and doing a simultaneous fit of the relevant Breit-Wigner terms in the measured energy region produced a modified set of resonance parameters. The extrapolation of the astrophysical S factor to lower energies is discussed on the basis of the unified data.

Proton angular distributions are measured for the exotic proton-halo nucleus 8B on a 58Ni target. The proton spectra are well described by statistical model calculations using the code PACE if both complete and incomplete fusion are taken into account. Fusion cross sections are deduced by using calculated proton multiplicities, a technique that is first successfully tested with the better known beam 6Li. The resulting fusion excitation function shows a large enhancement that requires a strikingly large barrier radius in order to be described, consistent with the assumption of a proton halo for 8B.

The cross section for \ensuremath{\alpha}-particle emission in the $^{6}\mathrm{He}+^{209}\mathrm{Bi}$ reaction at energies near the Coulomb barrier is remarkably large. Possible reactions that may produce the observed \ensuremath{\alpha} particles include two-neutron transfer, one-neutron transfer, and direct projectile breakup. Each of these mechanisms results in a distinctive angular correlation between the \ensuremath{\alpha} particle and the outgoing neutron(s). A neutron-\ensuremath{\alpha}-particle coincidence experiment was performed to study two-neutron transfer to unbound states of $^{211}\mathrm{Bi}$. It is shown that approximately 55% of the observed \ensuremath{\alpha}-particle yield at and beyond the grazing angle is because of this process. This is more than 2.5 times the fraction attributable to single-neutron transfer. The corresponding 2n-transfer cross section is 0.4 \ifmmode\pm\else\textpm\fi{} 0.1 b.

The elastic scattering of $^{10}\mathrm{Be}$ on $^{208}\mathrm{Pb}$ has been measured over a range of energies near the nominal Coulomb barrier. An excitation function for the total reaction cross section is obtained from the elastic-scattering angular distributions and compared with existing fusion data. Comparisons are also made with existing fusion, transfer∕breakup, and elastic data for $^{9}\mathrm{Be}$ incident on $^{209}\mathrm{Bi}$. A strong enhancement in the sub-barrier total reaction cross section for $^{9}\mathrm{Be+}^{209}\mathrm{Bi}$ relative to $^{10}\mathrm{Be+}^{208}\mathrm{Pb}$ is demonstrated.

In recent experiments, we have for the first time measured near‐barrier and sub‐barrier transfer and/or breakup yields for an exotic Borromean nucleus 6He, on a 209Bi target. An isolated 4He group was observed at an effective Q‐value of approximately −2.5 MeV whose integrated cross section was exceptionally large, greatly exceeding the fusion yield both above and below the barrier. Simultaneously measured elastic‐scattering angular distributions required total reaction cross sections that confirmed this large yield. Preliminary coupled‐channels calculations suggested that the reaction mechanism can best be described by direct breakup and neutron transfer to unbound states in 211Bi. The calculations also predicted an enhancement in the sub‐barrier fusion yield due to coupling to the transfer and/or breakup channel, which strongly suggested that this is the doorway state that accounts for the remarkable suppression of the fusion barrier that was observed in a previous experiment.

Recent near-barrier measurements for fusion of the proton-halo system 8B + 58Ni (Aguilera E F et al. 2011 Pys. Rev. Lett. 107 092701) showed unexpected results. In contrast to previous results for neutron-halo systems, for instance, the respective fusion cross sections are enhanced for both, below- and above-barrier energies. The charged nature of the halo could thus have an effect on the fusion mechanism. Within this context, in the present work the fusion cross sections for several proton rich systems are compared to each other. Three of these systems correspond to the same target, 58Ni (with projectiles of 3He, 7Be, and 8B), but data for 17F + 208Pb also are included. All these projectiles lie near the proton drip line. An appropriate scaling of the data is made to do the comparison and the results are discussed.

The interaction of ${}^{6}\mathrm{He}$ with ${}^{209}\mathrm{Bi}$ has been studied over a range of energies well below the nominal Coulomb barrier. A ${}^{4}\mathrm{He}$ group of remarkable intensity, first observed in a previous experiment at near-barrier energies, continues to dominate the reaction in the sub-barrier regime. A total cross section of nearly 200 mb was measured for this group at 6 MeV below the barrier. This very large value is shown to be consistent with the total reaction cross section deduced from a simultaneously-measured elastic scattering angular distribution.

Fusion excitation functions were obtained for ${}^{37}\mathrm{Cl}{+}^{70,72,73,74,76}\mathrm{Ge}$ at energies from about 6 MeV below to 7 MeV above the Coulomb barrier. The barrier parameters extracted from the data agree within 3% with those obtained from the systematics for fusion above the barrier. Low-energy enhancements are observed, whose behavior is explained within the context of simple model calculations by assigning appropriate degrees of freedom to the respective reaction partners. These degrees of freedom reflect the shape transition between spherical ${}^{70,72,73}\mathrm{Ge}$ and prolate-deformed ${}^{74,76}\mathrm{Ge},$ and show also remarkable effects of the odd-$A$ structure of ${}^{73}\mathrm{Ge}.$ The results are consistent with those of similar analysis of different data sets where the same targets were used. The possible effects of double identical-phonon states for spherical nuclei, hexadecapole deformations for deformed ones, and nucleon transfer are also examined. An analysis of the barrier distributions is made, which indicates consistency with the assumed degrees of freedom.

The angular momentum distribution of the compound nucleus is a fundamental characteristic of the reaction dynamics and can provide insight into reactions involving neutron- or proton-rich projectiles. Specifically, following the fusion of ${}^{6}\mathrm{He}$ with ${}^{209}\mathrm{Bi}$ (at center-of-mass energies of 18 to 27 MeV), ${}^{212}\mathrm{At}$ is formed by the evaporation of three neutrons from the compound nucleus. The decay process leaves the residual ${}^{212}\mathrm{At}$ in either the ground state ${(J}^{\ensuremath{\pi}}{=1}^{\ensuremath{-}},$ ${T}_{1/2}=314$ ms) or a metastable state ${(J}^{\ensuremath{\pi}}{=9}^{\ensuremath{-}},$ ${T}_{1/2}=119$ ms). The ratio of the number of residual ${}^{212m}\mathrm{At}$ to the total number of ${}^{212}\mathrm{At}$ residual nuclei is sensitive to the original momentum distribution of the compound nucleus. The measured isomer ratio is consistent with that predicted by standard models. This agreement is observed even at the lower energies where the measured three neutron evaporation cross section is greatly enhanced compared to model calculations. While the inclusion of coupling to the neutron-transfer channels improves the agreement with the observed cross-section data somewhat, the predicted isomer ratio then diverges from the measured ratio.

Yields of evaporated protons from the 8B+58Ni reaction are measured at backward angles, for several near barrier energies. Statistical model calculations using the code PACE are used to extrapolate the measurements to the whole angular region in order to get angle integrated cross sections. Fusion cross sections are deduced by using the calculated proton multiplicities. The obtained fusion excitation function shows a large enhancement as compared to BPM calculations using conventional barrier parameters.