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The isoscalar giant dipole resonance (ISGDR) in ${}^{208}\mathrm{Pb}$ has been investigated using inelastic scattering of 200 MeV $\ensuremath{\alpha}$ particles at and near 0\ifmmode^\circ\else\textdegree\fi{} where the angular distribution of the ISGDR can be clearly differentiated from those of other modes. The ``difference of spectra'' technique was employed to separate the ISGDR from the high-energy octupole resonance (HEOR). These data provide the clearest evidence yet for the ISGDR adjacent to the HEOR. With these results, all expected isoscalar $\ensuremath{\lambda}\ensuremath{\le}3$ resonances in ${}^{208}\mathrm{Pb}$ have been identified.

We used the $^{16}\mathrm{O}$${(}^{3}$He,n${)}^{18}$Ne, $^{12}\mathrm{C}$${(}^{12}$C${,}^{6}$He${)}^{18}$Ne, and $^{20}\mathrm{Ne}$(p,t${)}^{18}$Ne reactions to study $^{18}\mathrm{Ne}$ states up to an excitation energy of 10 MeV, with emphasis on levels corresponding to $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F and $^{17}\mathrm{F}$(p,\ensuremath{\gamma}${)}^{18}$Ne resonances that could strongly affect these reaction rates in hot stellar environments. Excitation energies, widths, absolute cross sections, and angular distributions were measured. We found previously unidentified states at ${\mathit{E}}_{\mathit{x}}$=6.15\ifmmode\pm\else\textpm\fi{}0.01 MeV, 7.12\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.35\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.62\ifmmode\pm\else\textpm\fi{}0.02 MeV, 8.30\ifmmode\pm\else\textpm\fi{}0.02 MeV, (8.45\ifmmode\pm\else\textpm\fi{}0.03 MeV), 8.55\ifmmode\pm\else\textpm\fi{}0.03 MeV, 8.94\ifmmode\pm\else\textpm\fi{}0.02 MeV, and 9.58\ifmmode\pm\else\textpm\fi{}0.02 MeV. We combined level width, cross section, and angular distribution data to infer ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ values for a number of the new levels as well as for the previously known 5.1-MeV doublet. Using information from our experiments, we recalculated the $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F reaction rate, which constitutes a possible path out of the hot CNO cycle into the rp process and could play an important role in transforming nuclei involved in the hot CNO cycle into heavier nuclei with Z\ensuremath{\ge}10. \textcopyright{} 1996 The American Physical Society.

The $^{6}\mathrm{Li}$${(}^{7}$Li${,}^{7}$Be${)}^{6}$He charge-exchange reaction leading to the neutron-halo nucleus $^{6}\mathrm{He}$ has been studied at E${(}^{7}$Li) = 350 MeV. Magnetic analysis was used to observe transitions to the known ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ = ${0}^{+}$ ground state and the ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ = ${2}^{+}$ state at ${\mathit{E}}_{\mathit{x}}$ = 1.8 MeV as well as pronounced resonances at \ensuremath{\sim}5.6 MeV, \ensuremath{\sim}14.6 MeV, and \ensuremath{\sim}23.3 MeV. Coincidences with 430-keV Doppler-shifted \ensuremath{\gamma} rays from the deexcitation in flight of the ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ = 1/${2}^{\mathrm{\ensuremath{-}}}$ first-excited state in $^{7}\mathrm{Be}$ were measured to permit the identification of spin-flip transitions. All observed transitions appear to have spin-flip characteristics. The shapes of the experimental angular distributions from ${\mathrm{\ensuremath{\theta}}}_{\mathrm{c}.\mathrm{m}.}$ = 0\ifmmode^\circ\else\textdegree\fi{} to 18\ifmmode^\circ\else\textdegree\fi{} are well described by microscopic one-step finite-range distorted-wave calculations with theoretical shell-model transition amplitudes. For the two low-lying shell-model states the absolute cross sections are also well described. The internal structures of the projectile and ejectile are taken into consideration. A large number of contributions is permitted by the angular momentum couplings. Only the ground state of $^{6}\mathrm{He}$ carries significant Gamow-Teller strength B(GT). Contributions with higher L values from the central spin flip and the tensor interactions ${\mathit{V}}_{\mathrm{\ensuremath{\sigma}}\mathrm{\ensuremath{\tau}}}$ and ${\mathit{V}}_{\mathit{T}\mathrm{\ensuremath{\tau}}}$ are responsible for the mostly structureless distributions observed, and the 0\ifmmode^\circ\else\textdegree\fi{} cross sections are not proportional to B(GT). The strong resonances at \ensuremath{\sim}5.6 MeV and \ensuremath{\sim}14.6 MeV are interpreted as ${2}^{+}$ and (1,2${)}^{\mathrm{\ensuremath{-}}}$ resonances, respectively, with cross sections stronger than predicted presumably due to mixing with continuum states leading to quadrupole and dipole enhancements. It appears that the resonance at \ensuremath{\sim}5.6 MeV does not represent a soft dipole mode originally predicted at ${\mathit{E}}_{\mathit{x}}$=4--7 MeV. \textcopyright{} 1996 The American Physical Society.

We have made simultaneous measurements of singles ($\stackrel{\ensuremath{\rightarrow}}{p}, {\stackrel{\ensuremath{\rightarrow}}{p}}^{\ensuremath{'}}$) spin-transfer observables and coincident ($\stackrel{\ensuremath{\rightarrow}}{p}, {p}^{\ensuremath{'}}\ensuremath{\gamma}$) yields and asymmetries for the 15.11 MeV, ${1}^{+}$, $T=1$ state in $^{12}\mathrm{C}$, at an incident proton bombarding energy of 200 MeV. Data were taken at four proton scattering angles ranging from ${\ensuremath{\theta}}_{p}^{\mathrm{c}.\mathrm{m}.}=5.5\ifmmode^\circ\else\textdegree\fi{} \mathrm{to} 16.5\ifmmode^\circ\else\textdegree\fi{}$. Both vertical (normal to the reaction plane) and horizontal (in-plane) incident beam polarizations were used, which allowed us to extract 16 different observables for this transition. In particular, using the ($\stackrel{\ensuremath{\rightarrow}}{p}, {p}^{\ensuremath{'}}\ensuremath{\gamma}$) reaction, we measured the sideways and longitudinal analyzing powers, ${D}_{0S}$ and ${D}_{0L}$, which vanish identically in the ($\stackrel{\ensuremath{\rightarrow}}{p}, {p}^{\ensuremath{'}}$) reaction. Detailed comparisons of all observables to calculations done in both relativistic and nonrelativistic formalisms are presented. Surprisingly, a relativistic description in which knock-on exchange processes are not explicitly included provides the best overall agreement with the data.

Fragmentation and splitting of the Gamow-Teller (GT) strength has been observed in a systematic study of the ${(}^{3}$He,t) charge-exchange reaction at E${(}^{3}$He)=200 MeV over the entire range of stable Sn isotopes. Triton energy spectra were observed with a high-resolution magnetic spectrometer at angles near \ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{} where \ensuremath{\Delta}L=0 transitions are enhanced. Excitation energies, widths, 0\ifmmode^\circ\else\textdegree\fi{} cross sections, and strengths B(GT) were determined. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components, expected to be dominant near A=118 at the onset of the filling of the 1${\mathit{h}}_{11/2}$ neutron orbital, could not be observed. This may be due to the fact that the total widths of the resonances of 5--6 MeV exceed the predicted splitting. A comparison of the 0\ifmmode^\circ\else\textdegree\fi{} cross sections for the transitions to the Gamow-Teller resonances and the isobaric analog states leads to strengths B(GT) for the main Gamow-Teller components of typically 65% of the sum-rule value of 3(N-Z). Three to four additional Gamow-Teller fragments (``pygmy resonances'') were observed in all final nuclei at lower excitation energies. The excellent energy resolution of the experiment made it possible to observe a pronounced fine structure in these low-lying resonances which is believed to be due to coupling to two-particle--two-hole doorway states. Also seen with all target nuclei was a systematic sequence of strong ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${1}^{+}$ states near the ground states in all Sb isotopes (${\mathit{E}}_{\mathit{x}}$=0 to 220 keV). In addition, strong \ensuremath{\Delta}L=1 resonances were observed in all nuclei at excitation energies of typically 20 MeV. Furthermore, nonresonant background from quasifree charge exchange was observed. An average of \ensuremath{\sim}85% of all excess neutrons seems to contribute to this background in approximate agreement with results from (e,e'p) experiments.

Equilibrium charge-state distributions for singly and doubly ionized [sup 3]He ions of energy [ital E]([sup 3]He)=200 MeV ([beta]=0.36) have been measured for atomic targets ranging from carbon to bismuth ([ital Z]=6,14,28,40,50,67,73,83). A magnetic spectrometer was used to simultaneously measure the rate of [sup 3]He[sup +] ions and the current of the incident beam of [sup 3]He[sup 2+] ions. The ratio of the fraction of ions [ital Y]([sup 3]He)[sup +]/[ital Y]([sup 3]He[sup 2+]) was found to increase from 3[times]10[sup [minus]9] for [ital Z]=6 to 2[times]10[sup [minus]7] for [ital Z]=83. Very good agreement with the experimental ratios was obtained for calculated ratios based on theoretical stripping (ionization) and capture cross sections. The cross sections are dominated by capture from [ital K] orbits only for atoms up to about [ital Z]=25. For target atoms with high [ital Z], contributions up to principal quantum numbers [ital n]=4 ([ital N] orbits) must be included.

In parallel experiments angular distributions of the differential cross sections and vector analyzing powers have been measured for the (d\ensuremath{\rightarrow}${,}^{3}$He) reactions on $^{204}\mathrm{Hg}$ and $^{206}\mathrm{Pb}$ at an incident deuteron energy of 79.1 MeV. The Q values for the reaction on $^{204}\mathrm{Hg}$ and a $^{202}\mathrm{Hg}$ contaminant were determined as -3340.9(3.4) keV and -2738.8(3.5) keV, respectively. Spectroscopic factors on $^{204}\mathrm{Hg}$ and $^{206}\mathrm{Pb}$ were obtained through a consistent distorted wave Born approximation (DWBA) analysis. A combined evaluation of relative spectroscopic factors and electron scattering (CERES) yields 3s-proton occupancies in $^{204}\mathrm{Hg}$ and $^{206}\mathrm{Pb}$. The latter is compatible with an earlier CERES result based on the more accurately known $^{206}--^{205}$Tl charge density difference. Substantial deviations from shell-model occupancies are observed.

Differential cross sections and analyzing powers for scattering of 200 MeV protons have been measured for states of $^{16}\mathrm{O}$ up to 14.4 MeV and for states of $^{40}\mathrm{Ca}$ up to 7.2 MeV of excitation. The data cover c.m. momentum transfers from approximately 0.4 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ to 3.0 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. Calculations were performed using several density-dependent effective interactions in the local density approximation. Empirical effective interactions from isoscalar normal-parity transitions were fitted to elastic and inelastic scattering data for $^{16}\mathrm{O}$ and $^{40}\mathrm{Ca}$ either individually or simultaneously. Transition densities from electron scattering were used to minimize uncertainties due to nuclear structure. The fitted interactions were iterated to generate optical potentials self-consistently. We find that the empirical interaction, although strongly dependent on the local density, is essentially independent of target or state. We also find that the empirical interaction is reduced in strength at zero density. Finally, the results were compared with a relativistic impulse approximation model and with a recent global optical potential from Dirac phenomenology.

Differential cross sections and analyzing powers were measured for $^{17}\mathrm{O}$(d\ensuremath{\rightarrow},t${)}^{16}$O with polarized deuterons of 89 MeV. States of $^{16}\mathrm{O}$ up to 22.89 MeV excitation energy have been studied with an overall resolution of 60 keV. Discrimination between analyzing powers (${\mathit{A}}_{\mathit{y}}$) for different j transfers was found to be very good. The unique ${\mathit{A}}_{\mathit{y}}$(\ensuremath{\theta}) shapes were used to deduce ${\mathit{p}}_{1/2}$-${\mathit{p}}_{3/2}$ mixing ratios for those levels where it was significant. We find unexpectedly strong mixing for the 6.130 MeV, ${3}^{\mathrm{\ensuremath{-}}}$, and 8.872 MeV, ${2}^{\mathrm{\ensuremath{-}}}$, levels. Exact finite-range distorted-wave Born approximation calculations were used to identify l transfers and to extract spectroscopic strengths. Up to 23 MeV excitation, pickup strength is dominated by 1p transfer; less than 2% of the observed particle-hole strength results from 2s, 1d, or 1f transfer. Twelve particle-hole matrix elements for (${\mathit{p}}_{1/2}^{\mathrm{\ensuremath{-}}1}$${\mathit{d}}_{5/2}$) and (${\mathit{p}}_{3/2}^{\mathrm{\ensuremath{-}}1}$${\mathit{d}}_{5/2}$) configurations have been deduced. Comparison with previous work shows general agreement except for the T=0,${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${3}^{\mathrm{\ensuremath{-}}}$ term.

The Gamow-Teller (GT) transition strengths in fp-shell nuclei are important parameters in presupernova models. A high-energy-resolution (He-3,t) experiment was performed on the T-z=1 nucleus Ti-46 at 0(degrees) and at an intermediate incident energy of 140 MeV/nucleon for the study of precise GT transition strengths to the final T-z=0 nucleus V-46. With an energy resolution of 33 keV, individual GT transitions were observed and GT strengths were derived for them up to the excitation energy of 4.5 MeV. The GT strengths were compared with shell-model calculations using various effective interactions. In this low-lying region, most GT states have isospin T=0. A few GT states with isospin T=1 were identified from the existence of the corresponding (analog) M1 states in Ti-46. By comparing the GT strength with the corresponding (analogous) M1 transition strength studied in Ti-46(e,e(')) or (gamma,gamma(')) measurements, a large constructive interference of orbital and spin terms was suggested for one of these M1 transitions.

A high energy-resolution $^{11}\mathrm{B}(^{3}\mathrm{He},t)^{11}\mathrm{C}$ experiment was performed at $0\ifmmode^\circ\else\textdegree\fi{}$ and an intermediate incident energy of $140\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{nucleon}$ for the study of precise Gamow-Teller (GT) transition strengths. Two doublet states at $\ensuremath{\approx}4.5$ and $\ensuremath{\approx}8.4\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ were clearly resolved with a resolution of $45\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. The strengths are compared with a calculation using an ab initio no-core shell model, which became available for the $A=11$ system recently. It was found that a calculation including a three-nucleon interaction better reproduces the observed GT transition strengths.

Inelastic excitation of giant resonances has been studied in 172 MeV $\ensuremath{\alpha}$ scattering from $^{208}\mathrm{Pb}$ at scattering angles of 1.5\ifmmode^\circ\else\textdegree\fi{}-8\ifmmode^\circ\else\textdegree\fi{}. Fine structures in the region of the giant monopole and quadrupole resonances indicate multipolarities also different from $L=0 \mathrm{and} 2$. The isoscalar $L=0 \mathrm{and} 2$ strengths in the giant resonance region yield (90\ifmmode\pm\else\textpm\fi{}20)% and (70\ifmmode\pm\else\textpm\fi{}20)% of the corresponding energy weighted sum rule limit. This is consistent with other hadron scattering results, with higher energy electron scattering, and with microscopic random phase approximation results. However, the strength for $L=2$ excitations is significantly larger than extracted from lower energy electron scattering. Fine structures observed are compared with high resolution (p,p\ensuremath{'}) and (e,e\ensuremath{'}) results. At scattering angles 5\ifmmode^\circ\else\textdegree\fi{}-8\ifmmode^\circ\else\textdegree\fi{} new structures have been observed at ${E}_{x}=12.5 \mathrm{and} 16.0$ MeV consistent with multipolarities $L=4 \mathrm{and} 6$. Together with the contribution of higher multipolarity extracted at lower excitation energies from the angular distributions of giant monopole and quadrupole excitations, this indicates rather broad distributions of $2\ensuremath{\hbar}\ensuremath{\omega}$ $L=4 \mathrm{and} 6$ excitations with centroid energies of 12.2 and 13.7 MeV and widths of 4.5 and 7.8 MeV, respectively. The extracted sum rule strengths for $L=4 \mathrm{and} 6$ are in the order of 30% in each case. In the region of the giant monopole resonance evidence for additional $L=2$ excitation was found (\ensuremath{\le}14% energy weighted sum rule strength). The fact that strong contributions of $Lg0$ are obtained solves the problem of a former too large monopole cross section in $\ensuremath{\alpha}$ scattering which was inconsistent with microscopic descriptions. A recently suggested "antiscaling" mode for the giant monopole resonance, in which the nuclear surface vibrates opposite in phase to the "scaling" mode, can be ruled out by our experimental data. The existence of two odd parity giant resonances at ${E}_{x}=18.7$ MeV ($L=3$) MeV ($L=1$) with widths of 5.0 and 5.9 MeV, respectively, are confirmed by our small angle scattering experiments. Our description of the dipole compressional mode is in excellent agreement with 200 MeV proton scattering data.NUCLEAR REACTIONS $^{208}\mathrm{Pb}(\ensuremath{\alpha}, {\ensuremath{\alpha}}^{\ensuremath{'}})$; ${E}_{\ensuremath{\alpha}}=172$ MeV. Small angle scattering, $\ensuremath{\theta}=1.5\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}8\ifmmode^\circ\else\textdegree\fi{}$; measured $\ensuremath{\sigma}(\ensuremath{\theta})$. Deduced excitation strength distributions for giant resonances of multipolarities $L=0\ensuremath{-}6$.

Differential cross sections and analyzing powers for/sup 15/N(/ital d/rvec //,/ital t/)/sup 14/N were measured up to 25MeV excitation energy with 88 and 89 MeV polarized deuteron beams and magneticspectrographs. States of /sup 14/N up to 18.53 MeV have been studiedin two experiments with overall resolutions of 25--70 keV, and /ital j/transfers were determined from their characteristic analyzing powers. Mixturesof different /ital j/ transfers could be determined for those 1/sup +/states where mixing was significant. Exact finite-range distorted-wave Bornapproximations calculations were used to deduce /ital l/ transfers andspectroscopic strengths. The observed summed spectroscopic strength is 88% ofthe shell-model sum rule. Firm lower limits and tentative upper limits for six(/ital p//sub 1/2/p/sub 1/2/)/sub J,/ital T// and(/ital p//sub 3/2/p/sub 1/2/)/sub J,/ital T// residual two-nucleonmatrix elements are deduced. Comparison with the widely used Cohen-Kurathmatrix elements shows good agreement for four terms, but significantquantitative disagreement for the(/ital p//sub 1/2/p/sub 1/2/)/sub 0/sup +/,1/ and(/ital p//sub 1/2/p/sub 3/2/)/sub 1/sup +/,1/ terms.We also see significantly more than the predicted/ital p//sub 1/2/p/sub 3/2/ mixing for the 3.948 MeV1/sup +/,0 state. No appreciable pickup of /ital s/-/ital d/shell admixtures was seen up to 25 MeV excitation.

Differential cross sections for /sup 208/Pb(p,p') and /sup 208/Pb(d,d') excitation of the 1/sup +/ state at E/sub x/ = 5.846 MeV were measured at E/sub inc/ = 45 MeV. The fact that the measured strengths of both reactions are very similar supports the isoscalar nature of the 1/sup +/ state. The comparison of the experimental proton angular distribution to microscopic distorted-wave calculations using random phase approximation wave functions with and without tensor correlations suggests that the isoscalar tensor part of the (..pi..+rho)-exchange potential is too strong.

The three-, four-, and five-nucleon transfers were investigated by studying the $^{10}\mathrm{B}$(\ensuremath{\alpha},${\mathrm{}}^{7}$Li${)}^{7}$Be, $^{11}\mathrm{B}$${(}^{3}$He${,}^{7}$Li${)}^{7}$Be, and $^{12}\mathrm{C}$(d${,}^{7}$Li${)}^{7}$Be reactions, respectively. The measurements were performed in the entire center of mass angular region, at incident energies corresponding to 49.3 MeV in the center of mass system of the exit channel. A distorted-wave Born approximation analysis was performed including second-order transfer contributions for all investigated reactions.

The yield of /sup 3/He/sup 1 +/ ions produced by a /sup 3/He/sup 2 +/ beam in C, Al, Ni, Ag, and Au foils was measured at 68, 99, and 130 MeV in order to determine the electron-capture cross sections sigma/sub c/. Measurements were performed using targets thicker than 60 ..mu..g/cm/sup 2/, where charge equilibrium was found. The results are compared with electron-stripping and -capture theories, which are found to explain fairly well the yield of /sup 3/He/sup 1 +/.