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Background: Heavy-ion induced two-nucleon transfer reactions are powerful tools to reveal peculiar aspects of the atomic nucleus, such as pairing correlations, single-particle and collective degrees of freedom, and more. Also, these processes are in competition with the direct meson exchange in the double charge exchange reactions, which have recently attracted great interest due to their possible connection to neutrinoless double-beta decay. In this framework, the exploration of two-nucleon transfer reactions in the 20Ne+116Cd collision at energies above the Coulomb barrier is particularly relevant since the 116Cd nucleus is a candidate for the double-beta decay. Methods: We measured the excitation energy spectra and absolute cross sections for the two reactions using the MAGNEX large acceptance magnetic spectrometer to detect the ejectiles. We performed direct coupled reaction channels and sequential distorted wave Born approximation calculations using the double folding S\~ao Paulo potential to model the initial and final state interactions. The spectroscopic amplitudes for two- and singleparticle transitions were derived by different nuclear structure approaches: microscopic large-scale shell model, interacting boson model-2 and quasiparticle random phase approximation. Results: The calculations are able to reproduce the experimental cross sections for both two-neutron and twoproton transfer reactions. The role of couplings with the inelastic channels are found to be important in the two-proton transfer case. A competition between the direct and the sequential process is found in the reaction mechanism. For the two-proton transfer case, the inclusion of the 1g7/2 and 2d5/2 orbitals in the model space is crucial.

Background: Resonances around $x\ensuremath{\alpha}$ thresholds in light nuclei are recognized to be important in basic aspects of nuclear structure. However, there is scarce experimental information associated with them.Purpose: We study the $\ensuremath{\alpha}$-clustering phenomenon in resonant states around the $4\ensuremath{\alpha}$ threshold (14.44 MeV) in the ${}^{16}\text{O}$ nucleus.Method: The ${}^{12}\text{C}{(}^{6}\text{Li},d){}^{16}\mathrm{O}$ reaction was investigated with an unprecedented resolution at a bombarding energy of 25.5 MeV by employing the S\~ao Paulo Pelletron-Enge-Spectrograph facility and the nuclear emulsion technique.Results: Several narrow resonances were populated and the energy resolution of 15 keV allows for the separation of doublet states that were not resolved previously. The upper limits for the resonance widths in this region were extracted. The angular distributions of the absolute differential cross section associated with four natural parity quasibound states are presented and compared to distorted wave Born approximation predictions.Conclusions: Narrow resonances not previously reported in the literature were observed. This indicates that the $\ensuremath{\alpha}$-cluster structure information in this region should be revised.

Taking {sup 94}Mo(d,d{sup {prime}}){sup 94}Mo(2{sub 1}{sup +}) at 13.2 MeV incident energy as an example, a discussion is made about the influence of known experimental uncertainties in the primary data on the precision of the B(E2) and B(IS2) values, extracted in Coulomb-nuclear interference (CNI) measurements in a correlated way. The reflexes of judicious variations of three optical model parameters (around the global prescription) on the extracted values are also examined. The good quality of the data obtained with the S. Paulo Pelletron-Enge-Spectrograph facility is shown to allow for a 2{endash}3{percent} statistical uncertainty level for these quantities, within a distorted-wave Born approximation-deformed optical model approach. The accuracy of relative values of the ratio B(E2)/B(IS2), which may be linked to the ratio of proton to neutron quadrupole moments, is argued to be of similar order. {copyright} {ital 1997} {ital The American Physical Society}

Coulomb-nuclear interference data for incident energies between 9 and 17 MeV were obtained in the form of elastic and inelastic (to the ${2}_{1}^{+}$ states) excitation functions of backscattered (\ensuremath{\theta}\ensuremath{\simeq}172.8\ifmmode^\circ\else\textdegree\fi{}) alpha particles on $^{100,102,104}\mathrm{Ru}$. The analysis was done in a distorted-wave Born approximation within a deformed optical model approach. B(E2) values, obtained from the charge deformation lengths ${\mathrm{\ensuremath{\delta}}}^{\mathit{C}}$ extracted from the low energy data, are compatible for the three isotopes within \ensuremath{\sim} 2\ensuremath{\sigma} with published values. The nuclear quadrupolar deformation lengths ${\mathrm{\ensuremath{\delta}}}^{\mathit{N}}$, obtained from the analysis of the interference region of the excitation functions, and also of one angular distribution at 22 MeV measured for $^{100}\mathrm{Ru}$ are generally lower than the corresponding charge deformation lengths, the difference increasing with increasing A of the isotope, ${\mathrm{\ensuremath{\delta}}}^{\mathit{N}}$ being 18% lower than ${\mathrm{\ensuremath{\delta}}}^{\mathit{C}}$ for $^{104}\mathrm{Ru}$ (${2}_{1}^{+}$). Nuclear deformation lengths associated with the ${3}_{1}^{\mathrm{\ensuremath{-}}}$ states of $^{100,102,104}\mathrm{Ru}$ and with the ${4}_{2}^{+}$ state of $^{100}\mathrm{Ru}$ at 2.367 MeV were also obtained as a by-product of the present work. \textcopyright{} 1996 The American Physical Society.

Ratios of $B(E2)$ to $B(IS2)$, that is, of the reduced quadrupole transition probabilities related, respectively, to charge and mass were extracted through Coulomb-nuclear interference (CNI) for the excitation of the ${2}_{1}^{+}$ states in $^{70,72,74}\mathrm{Ge}$, with a relative accuracy of less than 4%. For this purpose, the CNI angular distributions associated with the inelastic scattering of 28-MeV incident $^{6}\mathrm{Li}$ ions accelerated by the S\~ao Paulo Pelletron, and momentum analyzed by the Enge magnetic spectrograph were interpreted within the DWBA-DOMP approach (distorted wave approximation for the scattering process and deformed optical model for the structure representation) with global $^{6}\mathrm{Li}$ optical parameters. The present CNI results demonstrate an abrupt change in the $B(E2)/B(IS2)$ ratio for $^{74}\mathrm{Ge}$: although for $^{70,72}\mathrm{Ge}$, values of the order of 1.0 or slightly higher were obtained, this ratio is 0.66 (7) for $^{74}\mathrm{Ge}$. The heavier Ge isotope is thus one of the few nuclei that, so far, have been shown to present clear mixed symmetry components in their ground-state band.

The /sup 91/Zr(d,d')/sup 91/Zr( reaction has been investigated at 17 MeV incident energy. Up to 4.8 MeV excitation, 73 levels, some of them new, were identified. Angular distributions associated to approx.40 levels were attributed to pure L = 2, 3, or 5 excitations, concentrated in energy regions where the /sup 90/Zr core exhibits 2/sup +/, 3/sup -/, and 5/sup -/ states. The partial deformation parameters ..beta../sub L//sup prime/ obtained show agreement with those from low energy proton scattering for L = 2, but there is a systematic difference for L = 3 and L = 5, which is discussed. Attention is drawn to the high excitation probability of the first excited state of /sup 91/Zr, as measured by the ..beta../sub 2/approx. =0.18 value obtained, a factor of approx.2 above all other values for nuclei with A = 90 +- 2.

Levels in /sup 92/Zr were studied by a high resolution (d,p) reaction on /sup 91/Zr. Outgoing particles were momentum analyzed in a split-pole spectrograph and detected in nuclear emulsion plates. A total of 64 levels was identified up to about 5.4 MeV of excitation, several of them not previously reported. Experimental angular distributions were compared to distorted-wave Born-approximation predictions and reduced spectroscopic factors obtained. Energies of centers of gravity of each shell-model orbital were deduced and effective (d/sub 5/2/)/sup 2/ and (s/sub 1/2/d/sub 5/2/) neutron-neutron two-body diagonal matrix elements were estimated.

Energy levels of /sup 101/Ru have been studied by the /sup 100/Ru(d,p)/sup 101/Ru reaction at an incident deuteron energy of 12 MeV. Outgoing particles were momentum analyzed by a magnetic spectrograph and detected in nuclear emulsion plates, with an energy resolution of 7.5 keV. A total of 68 levels up to 3.2 MeV excitation energy was identified, about two-thirds of them reported for the first time. Experimental angular distributions were compared to distorted-wave Born approximation predictions and reduced spectroscopic factors obtained. The total l = 2 and 75% of l = 0, 4, and 5 spectroscopic strengths were located. Attention is drawn to transitions to low-lying states in /sup 101/Ru (below E/sub exc/ = 0.75 MeV) with l = 3 and l = 1 character.

Attention is drawn to the strong collective {ital L}=4 direct excitation of the state at 2.367 MeV in {sup 100}Ru by inelastic scattering of 16 MeV protons characterized by a deformation parameter {beta}{sub 4}=0.10, one of the highest reported for any region of the mass table.