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The Galactic 1.809-MeV $\ensuremath{\gamma}$-ray signature from the $\ensuremath{\beta}$ decay of $^{26g}\mathrm{Al}$ is a dominant target of $\ensuremath{\gamma}$-ray astronomy, of which a significant component is understood to originate from massive stars. The $^{26g}\mathrm{Al}(p,\ensuremath{\gamma})^{27}\mathrm{Si}$ reaction is a major destruction pathway for $^{26g}\mathrm{Al}$ at stellar temperatures, but the reaction rate is poorly constrained due to uncertainties in the strengths of low-lying resonances in $^{27}\mathrm{Si}$. The $^{26g}\mathrm{Al}(d,p)^{27}\mathrm{Al}$ reaction has been employed in inverse kinematics to determine the spectroscopic factors, and hence resonance strengths, of proton resonances in $^{27}\mathrm{Si}$ via mirror symmetry. The strength of the 127-keV resonance is found to be a factor of 4 higher than the previously adopted upper limit, and the upper limit for the 68-keV resonance has been reduced by an order of magnitude, considerably constraining the $^{26g}\mathrm{Al}$ destruction rate at stellar temperatures.

The degree to which the (p, γ) and (p,α) reactions destroy 18F at temperatures ∼ 1 − 4 × 10 8 K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide 18F, a target of gamma ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the 18F+p threshold ( E x = 6.411 MeV in 19Ne). To gain further information about these resonances, we have used the d(18F,p)19F neutron transfer reaction to selectively populate corresponding mirror states in 19F. The results would suggest 18F(p,γ)19Ne and 18F(p,α)15O reaction rates that are 2-3 times lower than reported previously.

Evaporation residue cross sections have been measured using neutron-rich radioactive 132Sn beams incident on a 64Ni target in the vicinity of the Coulomb barrier. This is the first experiment using accelerated 132Sn beams to study nuclear reaction mechanisms. The average beam intensity was 2x 104 particles per second and the smallest cross section measured was less than 5 mb. A large sub-barrier fusion enhancement was observed compared to evaporation residue cross sections for 64Ni on stable even Sn isotopes. The enhancement cannot be accounted for by a simple barrier shift due to the change in nuclear sizes. Coupled-channel calculations including inelastic excitation underpredict the measured cross sections below the barrier. The presence of several neutron transfer channels with large positive Q values suggests that multinucleon transfer may play an important role in enhancing the fusion of 132Sn and 64Ni.

Triple (p-p-fragment) coincidences from the $^{58}\mathrm{Ni}$${+}^{58}$Ni reaction at 850 MeV have been measured. By detecting the source of the emitted particles we were able to study the directional dependence of the p-p correlation function. From this dependence both the source size (${\mathit{r}}_{0}$) and the particle emission time (\ensuremath{\tau}) have been extracted. The extracted p-p correlation functions could be fitted with source size and lifetime in the range of 3.${3}_{\mathrm{\ensuremath{-}}0.7}^{+1.3}$ fm and 3.${2}_{\mathrm{\ensuremath{-}}2.2}^{+1.3}$\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}22}$ s, respectively.

Single-neutron-transfer measurements using (p,d) reactions have been performed at 33 MeV per nucleon with proton-rich Ar-34 and neutron-rich Ar-46 beams in inverse kinematics. The extracted spectroscopic factors are compared to the large-basis shell-model calculations. Relatively weak quenching of the spectroscopic factors is observed between Ar-34 and Ar-46. The experimental results suggest that neutron correlations have a weak dependence on the asymmetry of the nucleus over this isotopic region. The present results are consistent with the systematics established from extensive studies of spectroscopic factors and dispersive optical-model analyses of Ca40-49 isotopes. They are, however, inconsistent with the trends obtained in knockout-reaction measurements.

Intermediate mass fragment (IMF) production was studied in the inverse kinematics reaction [sup 58]Ni+[sup 27]Al at 15.8 MeV/nucleon bombarding energy using the Heavy Ion Light Ion (HILI) detector. Exit channels with up to 4 IMFs have been observed. The three-body events can be ascribed to different production mechanisms: (i) incomplete momentum transfer with projectile spectator breakup, (ii) sequential fission following a deep inelastic reaction, and (iii) fast sequential fission (i.e., with Coulomb final-state interaction) in competition with a prompt breakup out of a toroidal configuration. The identified ternary reaction mechanisms, covering an extremely wide dynamic range, could be observed simultaneously; a subgroup of events is compatible with an instantaneous breakup of a highly excited nuclear system.

The elastic angular distributions for [sup 58]Ni+[sup 27]Al have been measured at five energies from [ital E][sub c.m.]=48.8 to 69.5 MeV. The optical model analysis assumes both phenomenological and folding model potentials. Regions of sensitivity, where the potential is well determined, are found to be different for the real and the imaginary parts, and to vary with energy. The values of the real potential in the surface are weakly dependent on energy.

The influence of the neutron richness on binary decays is investigated in 78,82Kr+40Ca reactions at 5.5 MeV/A incident energy. Kinetic energy distributions and angular distributions of fragments with atomic number 6≤Z≤28 were measured using the 4π-INDRA array. Global features are compatible with an emission from a long-lived system. The yields around the symmetric splitting are about 30% smaller for the neutron rich system. The persistence of strong structural effects is evidenced from elemental cross-sections of the light fragments. The cross-sections for odd-Z fragments are higher for the neutron rich CN while cross-sections for even-Z fragments are higher for the neutron poor CN. Calculations assuming two different potential energy surfaces are presented

Exclusive {ital p}-{ital p} correlations from the {sup 58}Ni+{sup 58}Ni reaction at 850 MeV incident energy have been measured. The enhancement in the {ital p}-{ital p} correlation function observed for small values of {Delta}{ital p} with a gate on {ital v}{sub rel} is satisfactorily explained by stochastic proton emission followed by the {ital p}-{ital p} final-state interaction. A strong dependence of the {ital p}-{ital p} correlation function on the relative angle between the two-proton c.m. and the fragment velocities has been found. Also a dependence of the {ital p}-{ital p} correlation function on the {Delta}{bold p} orientation with respect to the plane defined by the two-proton c.m. and the fragment velocities has been observed. This latter behavior has been attributed to angular momentum effects.

The back-angle yields of the oxygen and carbon particles from the {sup 31}P+{sup 16}O reaction have been measured at {ital E}{sub lab}({sup 31}P)=135.6 MeV by using reverse kinematics. Comparison with similar data for the {sup 35}Cl+{sup 12}C reaction forming the same compound nucleus at the same excitation energy and with a very similar spin distribution shows very small entrance-channel dependence of back-angle yields. These results are in contrast to a similar study of the reactions {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O. It is evident that the oxygen and carbon yields from the {sup 31}P+{sup 16}O and {sup 35}Cl+{sup 12}C reactions have a predominantly compound nucleus origin in contrast to those from the {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O reactions. Possible connection of this nonequilibrium entrance channel dependence with the presence of nuclear molecular resonances is discussed.

Gamma-ray angular correlations have been measured for the strongly damped reactions {sup 12}C({sup 28}Si,{sup 12}C){sup 28}Si between {theta}{sub cm} = (120{degree} {minus} 160{degree}) for E{sub cm} = 43.5 and 48 MeV. We find that the density matrices for the {sup 12}C(2{sub 1}{sup +}) and {sup 28}Si states are almost diagonal with respect to the direction of motion of the outgoing particle. The measured density matrices and spin alignments are consistent with the picture of formation of a long-lived dinuclear complex undergoing orbiting, bending and wriggling motions, but not with those obtained from statistical compound nucleus or sticking model calculations. 17 refs., 2 figs., 1 tab.

Target and target-like ejectiles emitted forward from {sup 93}Nb-beam bombardment of thin {sup 50}Ti targets were investigated at sub- and near-barrier energies using a magnetic spectrograph. Reaction products from three single-nucleon-transfer and seven multinucleon-transfer channels were observed. Multinucleon-transfer products were observed with a sharp onset only for those collisions with apsidal distances smaller than about 12.6 fm, while single-nucleon-transfer products were observed throughout the apsidal distance range studied. Average {ital Q} values of the multinucleon-transfer-reaction products are much more negative than the respective optimum values. These results suggest the formation of a neck at subbarrier energies.

The time delays in fission induced by bombardment of W with 180 MeV $^{32}\mathrm{S}$, $240\text{\ensuremath{-}}255$ MeV $^{48}\mathrm{Ti}$, $330\text{\ensuremath{-}}375$ MeV $^{58}\mathrm{Ni}$, and 390 MeV $^{74}\mathrm{Ge}$ have been measured by observation of crystal blocking. Nearly all results are consistent with exponential decay with lifetimes of order ${10}^{\ensuremath{-}18}$ s which depend weakly on the atomic number of the composite nucleus. This is inconsistent with the Bohr-Wheeler model of fission from a compound nucleus in statistical equilibrium at each stage in a neutron evaporation cascade and supports a picture of strongly damped quasifission. A simple diffusion model with one-body dissipation reproduces roughly the observed time scale and the exponential decay. It suggests that the outer fission barrier could play a significant role in the observed, very slow decays.

Capture-fission cross sections were measured for the collision of the massive nucleus {sup 132}Sn with {sup 96}Zr at center-of-mass energies ranging from 192.8 to 249.6 MeV in an attempt to study fusion enhancement and hindrance in this reaction involving very neutron-rich nuclei. Coincident fission fragments were detected using silicon detectors. Using angle and energy conditions, deep inelastic scattering events were separated from fission events. Coupled-channels calculations can describe the data if the surface diffuseness parameter, a, is allowed to be 1.10 fm instead of the customary 0.6 fm. The measured capture-fission cross sections agree moderately well with model calculations using the dinuclear system model. If we use this model to predict fusion barrier heights for these reactions, we find the predicted fusion hindrance, as represented by the extra push energy, is greater for the more neutron-rich system, lessening the advantage of the lower interaction barriers with neutron-rich projectiles.

Measurements of the fusion cross sections in the barrier and subbarrier regions are presented for the four heavy-ion systems $^{46,50}\mathrm{Ti}$${+}^{90}$Zr${,}^{93}$Nb. The measured cross sections varied from 0.04 to 400 mb. The evaporation residues were detected by the use of a velocity filter. Procedures are described for extracting fusion cross sections from such measurements. The observed differences in the subbarrier fusion cross sections for the $^{90}\mathrm{Zr}$ and $^{93}\mathrm{Nb}$ nuclei, both of which have small collectivity, have led us to question the view that excursions of the strong nuclear force due to collective motions of the colliding nuclei are the primary enhancement mechanisms for the observed heavy-ion subbarrier fusion cross sections.A simple formula is presented, based on a flat distribution of barriers, which is applied to the near-barrier region (10--200 mb). This formula states that the quantity (\ensuremath{\sigma}E${)}^{1/2}$ vs E is linear in the near-barrier region with a zero intercept defining a threshold energy for fusion. These threshold values reflect variations in the binding energies of the valence neutrons. We also point out that the far-subbarrier region (10 mb) shows large variations in fusion cross sections and that these variations reflect differences in the collectivities of the colliding nuclei (especially noticeable differences are seen between permanently deformed nuclei and ``vibrational'' nuclei). These systematics of heavy-ion subbarier fusion suggest that neck formation is playing an important role. The barrier for neutron transfer vanishes at distances typically 1.5 fm beyond the typical barrier distance and this distance could vary with the binding energy of the valence neutrons. The presence of neutrons in the region between the nuclei could promote neck formation which provides a force strong enough to overcome the Coulomb force. The collective properties of the colliding nuclei are then interpreted as a modulation of the threshold for neck formation and thereby reflect the large observed differences in the far-subbarrier cross sections. Formulas are presented for ${\mathrm{\ensuremath{\sigma}}}_{\mathit{L}}$ which result from a flat distribution of barriers. These formulas predict a broad bell-shaped spin distribution and are compared to the measured distribution in the subbarrier region for the system $^{64}\mathrm{Ni}$${+}^{100}$Mo.

Excited states in the N = Z+1 nucleus Y-79 Were identified using the reaction Si-28(Fe-54, p2n)Y-79 at a 200 MeV beam energy and an experimental set up consisting of an array of Ge detectors and the Recoil Mass Spectrometer at Oak Ridge National Laboratory. With the help of additional gamma-gamma coincidence data obtained with Gammasphere, these gamma-rays were found to form a strongly-coupled rotational band with rigid-rotor-like behavior. Results of conventional Nilsson-Strutinsky cranked shell model calculations, which predict a deformation of beta(2)similar to 0.4, are in excellent agreement with the properties of this band. Similar calculations for the neighboring N = Z and N = Z + 1 nuclei are also in good agreement with experimental data. This suggests that the presence of the putative T = 0 neutron-proton pairing does not significantly affect such simple observables as the moments of inertia of these bands at low spins. (Less)

We have studied the evolution towards mass equilibration in {sup 24}Mg+{sup 16}O orbiting interactions. {sup 24}Mg beams of energies between 75 and 115 MeV were used to bombard targets of {sup 16}O. Targetlike particles were detected at forward angles to determine the yields from orbiting interactions. The ratio of the orbiting yields of {sup 12}C and {sup 16}O exit channels rises continuously with energy from values below unity to above. The data are interpreted as demonstrating a strong entrance channel dependence at low energies, and an evolution towards mass equilibration with increasing energy.

Breakup of 63-MeV and 42-MeV {sup 7}Li near the {alpha}-{ital t} threshold is examined from the astrophysical point of view. A new approach is made to extract indirectly astrophysical {ital S} factors. The {ital S} factors are compared with those deduced from radiative-capture measurements. It is shown that the energy dependence favors the recent capture data of Schroeder {ital et} {ital al}.

The differential cross section for the excitation of the unbound 3/sup +/ (2.18 MeV) state in /sup 6/Li was measured by scattering a 227 MeV /sup 40/Ca beam from a /sup 6/Li target. Additionally, the cross section for the 3/sup -/ (3.74 MeV) state in /sup 40/Ca was measured at the same center-of-mass energy by scattering a 34 MeV /sup 6/Li beam from /sup 40/Ca. The cross section for excitation of the 3/sup +/, 2.18 MeV state in /sup 6/Li is 3--5 times larger than that of the /sup 40/Ca 3/sup -/ state. The present data and previously measured elastic scattering data have been analyzed in the framework of both distorted-wave Born approximation and coupled channels calculations, using double folded real potentials, to determine the influence of the inelastic states on the elastic scattering cross section. We find that the elastic scattering is very sensitive to coupled channels effects arising from the 3/sup +/ state in /sup 6/Li.

The one-nucleon transfer reactions /sup 28/Si(/sup 18/O,/sup 17/O)/sup 29/Si and /sup 28/Si( /sup 18/O,/sup 19/F)/sup 27/Al have been studied at 352 MeV bombarding energy. Several strong transitions were identified in each reaction and analyzed using the distorted-wave Born approximation. A shallow, surface-transparent optical potential of E-18 type did not give acceptable results, but deeper, more conventional potentials fitted the data without any need for renormalization. Data on the same reactions taken earlier at 56 MeV were reanalyzed and the results compared to the present experiment. The use of the distorted-waves approximation is examined critically.

Angular correlations between ..cap alpha.. particles and evaporation residues have been measured to study the equilibrium versus nonequilibrium effects on the fusion process. Measurements with ..cap alpha..-particle detectors were carried out to extreme forward angles (4/sup 0/) to maximize the sensitivity to nonequilibrium components. The results are consistent with complete fusion and equilibrium decay, in contrast with recent systematics that predict large amounts of incomplete fusion at this energy.

Fusion cross sections for the /sup 14/N+/sup 13/C system have been measured by detecting the evaporation residues at five bombarding energies which correspond to high excitation energies in the compound nucleus: E*(/sup 27/Al) = 64--110 MeV. The /sup 27/Al nucleus can be populated by four different heavy-ion entrance channels: /sup 15/N+ /sup 12/C, /sup 16/O+/sup 11/B, /sup 14/N+/sup 13/C, and /sup 17/O+/sup 10/B: which are accessible to experimental measurements. Comparing the present data with those already existing for the above channels, it is found that for E*>60 MeV the curves E* vs J/sub cr/ for each system converge, which may be indicative of a limitation imposed by the compound nucleus. The data are discussed in terms of existing models for entrance channel and statistical yrast line limitations. The highest energy point also suggests the existence of a maximum absolute angular momentum limit of approx.28h.

Cross sections for the fusion of $^{28}\mathrm{C}$ have been measured at center of mass bombarding energies of 39, 43.5, 48, and 54 MeV. Velocity and energy spectra of reaction products having charge Z\ensuremath{\ge}12 and mass number A\ensuremath{\ge}24 were studied at several angles between ${\mathrm{theta}}_{\mathrm{lab}=2\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}$ and 13\ifmmode^\circ\else\textdegree\fi{}. Separation of fusion from other processes was made by comparison of kinematic calculations to measured spectra. The extracted critical angular momentum (${l}_{\mathrm{cr}{}^{\mathrm{fus})}}$ of 22\ensuremath{\Elzxh} indicates the existence of an entrance-channel-imposed limit on the high energy fusion cross section. More symmetric systems forming the same compound nucleus, $^{40}\mathrm{Ca}$, have considerably larger limiting angular momenta. This result is consistent with the previous observation of a maximum angular momentum of 22\ensuremath{\Elzxh} (relative to the entrance channel) for the orbiting dinuclear complex found in studies of back-angle deeply inelastic scattering of $^{28}\mathrm{Si}$ and $^{12}\mathrm{C}$.

The elastic and inelastic scattering of 18 O ions at 120 MeV from a target of 208 Pb have been studied. Cross sections for excitation of the 2 + state at 1.982 MeV in 18 O and of the 3 − state at 2.61 MeV in 208 Pb were measured. In addition, the populations of the m -substates for the 18 O excitation were deduced from the Doppler-broadened line shapes. The data were subjected to a coupled-channels analysis using either Woods-Saxon or folding-model potentials. In addition, the 18 O excitation was found to be described very well by use of a semi-microscopic model. The analyses consistently indicated the presence of a positive static hexadecapole moment of several e · fm 4 for the 2 + state of 18 O. The m -substate population distributions were found to be better fitted if a vector spin-orbit coupling was introduced for the 2 + state of 18 O with a sign opposite to that for the nucleon-nucleus case.

Excitation functions at 7° (lab) have been measured from E c.m. = 5.1 to 11.4 MeV in approximately 114 keV steps for 15 groups of final states in 17 O populated by the 12 C( 9 Be, α) reaction. Statistical tests have been used to locate possible non-statistical structure in the excitation functions. Possible anomalies were found near E c.m. = 6.3, 7.5, 8.9 and 9.7 MeV. Angular distributions were measured at E c.m. = 9.20, 9.71 and 10.23 MeV for the three lowest excited states in 17 O. The data have been compared with Hauser-Feshbach calculations in addition to the following reaction mechanisms: compound plus a single resonance, compound plus interfering resonances and compound plus direct reactions.

Fusion cross sections were measured for the $^{12}\mathrm{C}$ + $^{15}\mathrm{N}$ system at two $^{12}\mathrm{C}$ bombarding energies, 98 and 117 MeV. The extracted fusion cross sections are 946 \ifmmode\pm\else\textpm\fi{} 74 mb for $E(^{12}\mathrm{C})=98$ MeV and 889 \ifmmode\pm\else\textpm\fi{} 89 mb for $E(^{12}\mathrm{C})=117$ MeV. The critical angular momenta for fusion deduced from the cross section measurements equal, within $1\ensuremath{\hbar}$, the values deduced from $^{14}\mathrm{N}$ + $^{13}\mathrm{C}$ and $^{10}\mathrm{B}$ + $^{17}\mathrm{O}$ at the same excitation energies, thus indicating a compound nucleus limitation for fusion.NUCLEAR REACTIONS $^{12}\mathrm{C}$ + $^{15}\mathrm{N}$, $E(^{12}\mathrm{C})=98 \mathrm{and} 117$ MeV; gas cell target; measured $\frac{{d}^{2}\ensuremath{\sigma}}{d\ensuremath{\Omega}\mathrm{dE}}$ for reaction products with $Z=7 \mathrm{to} 12$. Extracted ${\ensuremath{\sigma}}_{\mathrm{fus}}$.

Forward-angle yields of targetlike products in reactions between a /sup 28/Si beam and a /sup 14/N target have been measured at laboratory energies between 100 and 170 MeV. The /sup 12/C and /sup 16/O yields are found to be higher than those of /sup 14/N over the measured range of energies. This is interpreted as evidence for the equilibration of charge and mass in orbiting reactions.

A transport theory is developed for description of capture processes in low-energy nuclear collisions. It is based on the picture that a dinuclear molecular complex formed during early stages of the collision acts as a doorway configuration toward formation of a fully equilibrated compound nucleus, and this complex can decay into open binary channels while it evolves toward a compound nucleus. The evolution of the dinuclear molecular complex and its decay into binary fragmentation channels are determined by two coupled transport equations. The formalism, in a local equilibrium limit, is successfully applied to analyze complex fragment emission and fusion-evaporation data from collisions of Si+C, Si+N, and Mg+C.

The most probable value for the total kinetic energy of reaction products from strongly damped collisions of $^{28}\mathrm{Si}$ + $^{12}\mathrm{C}$ was found to increase with bombarding energy only up to a limiting value. This behavior suggests that the orbital angular momentum of the dinuclear complex formed in these collisions has reached a saturation value beyond which further increase is not possible.

An experimental study of the /sup 20/Ne+/sup 12/C systems reveals a large cross section for inelastic scattering with large negative Q-values at backward angles. The differential cross section is proportional to l/sin theta/sub c.m./ for theta/sub c.m./>100/sup 0/ and has characteristics consistent with the decay of an orbiting /sup 20/Ne+/sup 12/C dinuclear system.

Results are presented for 350- and 400-MeV /sup 16/O inelastic scattering from /sup 208/Pb and /sup 90/Zr. The results show excitation of the giant quadrupole, monopole, and dipole resonances. The cross section and peak to continuum ratio are very large for the giant quadrupole resonance. Measured angular distributions agree with distorted-wave Born approximation calculations which use standard collective model form factors. Structure observed in the /sup 16/O spectra corresponding to high excitation energies in /sup 208/Pb is shown to arise from projectile pickup reactions.

Differential cross sections for the /sup 25/Mg(/sup 12/C,/sup 9/Be) reaction were measured at theta/sub L/=10, 15, 20/sup 0/ for bombarding energies near 100 and 120 MeV. These data are consistent with direct /sup 3/He transfer to highly excited, high-spin states in /sup 28/Si. The energy spectra, angular distributions, level systematics of sd-shell nuclei, and shell-model calculations strongly suggest that a state observed at 15.8 MeV is the previously unidentified 8/sup +/ member of the ground-state rotational band of /sup 28/Si.

Cross sections for the fusion of /sup 28/Si+/sup 12/C and /sup 30/Si+/sup 12/C have been measured at energies between 6.4 and 9.4 MeV/nucleon and 5.2 and 8.3 MeV/nucleon, respectively. Comparison with existing data for compound systems with A = 40 and 42 shows that the extracted critical angular momentum at saturation (l/sub cr//sup max/) depends strongly on the entrance channel mass asymmetry. This effect is not accounted for by the standard entrance channel or compound nucleus models. A calculation of the conditional saddle-point shapes for touching spheroidal nuclei indicates that this mass asymmetry effect is a consequence of the dynamical fusion thresholds at high angular momentum. Quantitative agreement is obtained with the experimentally measured l/sub cr//sup max/ using the finite range model of Sierk for diffuse-surface nuclei.

The fusion cross section for /sup 10/B+/sup 17/O has been measured at five exitation energies in /sup 27/Al of E* = 48.4, 55.1, 66.9, and 74.4 MeV in order to study possible compound nucleus limitation effects on fusion for light heavy-ion systems at intermediate excitation energies. Comparing this data with other measurements for different entrance channels populating the same compound nucleus it is found that for E* 60 MeV the bands tend to converge indicating a possible compound nucleus limitation effect. The data are compared with existing models for entrance channel and statistical yrast line limitations.

All reaction products with Z> or =5 emitted from the bombardment of /sup 12/C by /sup 20/Ne beams with incident energies between 54 and 80 MeV have been measured over a wide range of exit energies and angles. The quasielastic, strongly damped, and complete fusion processes were studied. At forward angles both the elastic and inelastic data show the effect of strong volume absorption. At larger angles the paucity in open direct channels manifests itself by a resonantlike behavior of the excitation functions for all outgoing channels reminiscent to that observed for /sup 16/O+/sup 16/O. The energy dependence of the cross section for complete fusion also shows structure, but the average magnitude of the /sup 20/Ne+/sup 12/C fusion cross section is 1100 mb compared to 900 mb for /sup 16/O+/sup 16/O. At backward angles the /sup 20/Ne+/sup 12/C quasielastic angular distribution and excitation functions show the same characteristics seen in heavier systems (e.g., /sup 28/Si+/sup 12/C). However, a much larger yield exists for transitions to high excitation energies (large negative Q values). This strongly damped process has a large cross section and shows all the characteristics of a long lived orbiting /sup 20/Ne+/sup 12/C dinuclear system.

The differential cross sections of proton-pickup reactions on /sup 40/Ca initiated by various heavy-ion projectiles have been uniformly analyzed in a distorted-wave Born-approximation model. There appears to be a spectroscopic-factor inconsistency depending on whether an odd-odd or an even-even nucleus (projectile or ejectile) participated in the reaction.

Reaction products from the bombardment of /sup 20/Ne and /sup 16/O gas targets with /sup 20/Ne beams have been measured at five laboratory energies between 70 and 160 MeV. Fusion, deep inelastic, and quasielastic processes were studied. Large deep inelastic yields (sigma/sub DI/> or approx. =600 mb) with average Q values of -50 MeV are present at the highest energy. Analysis of the fusion cross sections for /sup 20/Ne+ /sup 16/O suggests that the maximum angular momentum in /sup 36/Ar populated via this entrance channel may be as low as 29 +- 2h.

The analysis of quasielastic cross section data for the /sup 90/Zr projectile plus /sup 50/Ti target system shows that the probability for /sup 50/Ti(/sup 90/Zr, /sup 49/Ti)/sup 91/Zr, 1n-transfer reaction near the barrier is much larger than estimates based on semiclassical theory. The probability for /sup 50/Ti(/sup 90/Zr,/sup 51/V)/sup 89/Y, 1p-transfer reaction, on the other hand, agrees with the same theory. The internuclear distance where the 1n-transfer probability first deviates from tunneling predictions coincides with the threshold of the fusion barrier distribution deduced from the experimental fusion cross sections of the /sup 50/Ti+/sup 90/Zr system, suggesting a common mechanism for the large enhancement of 1n-transfer and fusion cross sections.

The cross section for fusion of $^{10}\mathrm{B}$+$^{16}\mathrm{O}$ is found to differ markedly from that of $^{12}\mathrm{C}$+$^{14}\mathrm{N}$ for bombarding energies in the range 3 to 9 times the fusion barrier. This difference exceeds that expected on the basis of calculated or measured nuclear density distributions for these nuclei.

The fusion cross section of the /sup 10/B+/sup 14/N system has been measured at five energies covering the range E/sub 14N/ = 86-180 MeV. Angular distributions of fusion and direct reaction components for products from Z = 3 to Z = 11 have been determined. Hauser-Feshbach calculations of the Z distributions, energies and angular distributions of the evaporation residues are presented and compared to the data. The fusion cross section decreases slowly with increasing energy and reaches a maximum angular momentum of about 21 +- 1 h. The fusion cross section is discussed in terms of entrance channel models and compound nucleus formation and is compared to that of the /sup 12/C+/sup 12/C system. The experimental total reaction cross sections are in good agreement with optical model calculations with parameters deduced from elastic scattering.

Direct E2 and multiple Coulomb excitation of states up to J=9/2 in the K=1/2 and K=3/2 bands of /sup 183/W has been measured by means of ..gamma..-ray spectroscopy. Excitation was produced by 15-MeV /sup 4/He ions on a thick target of W with natural abundance. Excitation probabilities were also determined relative to the elastic scattering by the observation of the (..cap alpha..,..cap alpha..') reaction on /sup 183/W with 13-MeV /sup 4/He ions using a split-pole magnetic spectrometer equipped with a position-sensitive proportional detector. The B (E2) values for excitation of the 3/2/sup L/, 5/2/sup L/, 3/2/sup H/, and 5/2/sup H/ states (H and L refer to the high and low energy states of the same total angular momentum J) are obtained and information is given on the reduced transition probabilities for the different decay modes of these states. In particular, the prediction of strong cancellation in the E2 transition probabilities for the 3/2/sup H/ ..-->.. 1/2/sup L/, 3/2/sup H/ ..-->.. 5/2/sup L/, and 5/2/sup H/ ..-->.. 5/2/sup L/ transitions from Coriolis interaction calculations has been verified by the experimental results. The experimental results are compared with several calculations of the Coriolis coupling between the rotational bands. Several weakly excited statesmore » between 0.9 and 1.5 MeV were observed and the B (E2) for excitation of these states are < or = B (E2)/sub s.p./.« less

New data on resonances in the /sup 12/C + /sup 16/O system are presented. A systematic pattern is observed suggesting that theoretical models, which have recently been formulated for the mechanism of resonances appearing in the /sup 12/C + /sup 12/C system, also apply to this system. Furthermore, energies, spins, and widths for entrance-channel resonances predicted by a recent microscopic calculation of /sup 12/C + /sup 16/O scattering agree very well with the data presented here.

The charge and mass distribution of orbiting yields from the /sup 28/Si+ /sup 14/N interaction have been studied at center of mass energies between 30 and 56.7 MeV. The data indicate that the orbiting system lives sufficiently long for the exit channel yields to be determined by phase space considerations. The data are compared with compound nucleus and orbiting calculations, and clearly favor the latter. Further comparisons between the data and the orbiting calculations indicate that full phase space equilibration of the orbiting yields is hindered at low excitation energies by the inaccessibility of single nucleon transfer channels. Also evident in the data is a correlation in the behaviors of the charge width, mass width, and final product kinetic energies, which is interpretable as arising from a maximum angular momentum that the /sup 28/Si+ /sup 14/N orbiting composite can sustain.

Excitation functions were measured for states of 21 Ne populated by the 12 C ( 13 C , α) reaction over the bombarding energy range E lab = 18.2–32.0 MeV (18.4–27.0 MeV) at θ lab = 7°(25°) in in 200 keV steps, and average coherence widths of states and the moment of inertia of the compound nucleus 25 Mg were obtained from these excitation functions. A statistical analysis of these data was performed. Angular distributions for states in 21 Ne to 10 MeV in excitation energy were measured at θ lab = 7°, 18°, 28° and 43° at bombarding energies from 29.0 to 31.0 MeV in 400 keV steps. These data along with Hauser-Feshbach predictions allow us to suggest spins for some states as well as to suggest possible candidates for rotational bands in 21 Ne.

Differential cross sections have been measured for the elastic and inelastic scattering of $^{18}\mathrm{O}$ from $^{28}\mathrm{Si}$ at 352 MeV. An optical model analysis has been performed for the elastic scattering data. Considerable ambiguity was found. Potentials which are either transparent or strongly absorbing in the surface region were obtained which give equally good fits to the data. The combined elastic and inelastic data were subjected to a coupled-channels analysis and the ambiguity was found to persist, in contrast to previously reported one-nucleon transfer data whose analysis allowed us to discriminate between the two types of potential. Other characteristics of the scattering are discussed.

Reactions induced by bombarding a /sup 16/O gas target with /sup 27/Al ions were studied. Evaporation residues as well as target-like recoils were measured over a wide range of Q values. The yield of particles with 6< or =Z< or =9 was found to be forward peaked in the laboratory frame. These target-like particles emerge with center-of-mass kinetic energies that, on the average, are independent of the reaction angle. Their combined cross section has a 1/sintheta/sub c.m./ angular dependence. If this cross section is assumed to be symmetric about 90/sup 0/ (c.m.) the integrated cross section is about 10% of the measured evaporation residue cross section at a center-of-mass energy of 54 MeV.

The /sup 208/Pb high excitation continuum has been studied using inelastic scattering of 22 MeV/nucleon /sup 17/O and /sup 32/S. The spectra, taken with a magnetic spectrograph, show no evidence for peaks in the 30--100 MeV region of excitation in contrast to published results. The /sup 17/O spectra are found to be remarkably similar to those from medium energy proton scattering.

We present a model that provides a unified description of fusion and the full momentum transfer component of dissipative collisions (orbiting), in light-heavy-ion-induced reactions. The model is applied successfully to describe measured cross sections for fusion and orbiting over a wide range of bombarding energies for the /sup 28/Si+/sup 12/C system.