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Register a new userSpin-dipole strengths and tensor correlation effects for ${}^{208}{rm Pb}(p,n)$ at 295 MeV
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T. Wakasa
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We performed the multipole decomposition analysis (MDA) for the ${}^{208}{rm Pb}(p,n)$ data in order to obtain the spin-dipole (SD) strengths separated into each $Delta J^{pi}$ contribution $dB({rm SD}_{Delta J^{pi}};omega)/domega$. The random phase approximation (RPA calculations reproduce the total SD strength reasonably well, whereas some discrepancies are found for separated SD strength. The centroids of the resonances are slightly lower and higher than the theoretical predictions for $1^-$ and $2^-$, respectively. These softening and hardening effects observed in $1^-$ and $2^-$ distributions would be due to the tensor correlation effects not included in the present RPA calculations.
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Differential cross sections and complete sets of polarization observables are presented for the Gamow-Teller $^{12}{rm C}(vec{p},vec{n})^{12}{rm N}({rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV with momentum transfers $q$ of 0.1 to $2.2{rm fm}^{-1}$. The polarization transfer observables are used to deduce the spin-longitudinal cross section, $ID_q$, and spin-transverse cross sections, $ID_p$ and $ID_n$. The data are compared with calculations based on the distorted wave impulse approximation (DWIA) using shell-model wave functions. Significant differences between the experimental and theoretical results are observed for all three spin-dependent $ID_i$ at momentum transfers of $q gtrsim 0.5{rm fm}^{-1}$, suggesting the existence of nuclear correlations beyond the shell model. We also performed DWIA calculations employing random phase approximation (RPA) response functions and found that the observed discrepancy is partly resolved by the pionic and rho-mesonic correlation effects.
Background: The influence of halo structure of $^6$He, $^8$B, $^{11}$Be and $^{11}$Li nuclei in several mechanisms such as direct reactions and fusion is already established, although not completely understood. The influence of the $^{10}$C Brunnian structure is less known. Purpose: To investigate the influence of the cluster configuration of $^{10}$C on the elastic scattering at an energy close to the Coulomb barrier. Methods: We present experimental data for the elastic scattering of the $^{10}$C+$^{208}$Pb system at $E_{rm lab}$ = 66 MeV. The data are compared to the three- and the four-body continuum-discretized coupled-channels calculations assuming $^9$B+$p$, $^6$Be+$alpha$ and $^8$Be+$p$+$p$ configurations. Results: The experimental angular distribution of the cross sections shows the suppression of the Fresnel peak that is reasonably well reproduced by the continuum-discretized coupled-channels calculations. However, the calculations underestimate the cross sections at backward angles. Couplings to continuum states represent a small effect. Conclusions: The cluster configurations of $^{10}$C assumed in the present work are able to describe some of the features of the data. In order to explain the data at backward angles, experimental data for the breakup and an extension of theoretical formalism towards a four-body cluster seem to be in need to reproduce the measured angular distribution.
We report measurements of the cross section and a complete set of polarization observables for the Gamow--Teller ${}^{12}{rm C}(vec{p},vec{n}){}^{12}{rm N}({rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV. The data are compared with distorted wave impulse approximation calculations employing transition form factors normalized to reproduce the observed beta-decay $ft$ value. The cross section is significantly under-predicted by the calculations at momentum transfers $q gtrsim $ 0.5 ${rm fm^{-1}}$. The discrepancy is partly resolved by considering the non-locality of the nuclear mean field. However, the calculations still under-predict the cross section at large momentum transfers of $q$ $simeq$ 1.6 ${rm fm^{-1}}$. We also performed calculations employing random phase approximation response functions and found that the observed enhancement can be attributed in part to pionic correlations in nuclei.
The cross-sections and analyzing powers for $(p,n)$ reactions on ${}^{3}{rm He}$ and ${}^{4}{rm He}$ have been measured at a bombarding energy of $T_p$ = 346 MeV and reaction angles of $theta_{rm lab}$ = $9.4^{circ}$--$27^{circ}$. The energy transfer spectra for ${}^{3}{rm He}(p,n)$ at large $theta_{rm lab}$ ($ge$ $16^{circ}$) are dominated by quasielastic contributions, and can be reasonably reproduced by plane-wave impulse approximation (PWIA) calculations for quasielastic scattering. By contrast, the known $L$ = 1 resonances in ${}^{4}{rm Li}$ are clearly observed near the threshold in the ${}^{4}{rm He}(p,n)$ spectra. Because these contributions are remarkable at small angles, the energy spectra are significantly different from those expected for quasielastic scattering. The data are compared with the PWIA calculations, and it is found that the quasielastic contributions are dominant at large $theta_{rm lab}$ ($ge$ $22^{circ}$). The nuclear correlation effects on the quasielastic peak for ${}^{4}{rm He}(p,n)$ are also discussed.
A previous study of symmetric collisions of massive nuclei has shown that current models of multi-nucleon transfer (MNT) reactions do not adequately describe the transfer product yields. To gain further insight into this problem, we have measured the yields of MNT products in the interaction of 977 (E/A = 4.79 MeV) and 1143 MeV (E/A = 5.60 MeV) $^{204}$Hg with $^{208}$Pb. We find that the yield of multi-nucleon transfer products are similar in these two reactions and are substantially lower than those observed in the reaction of 1257 MeV (E/A = 6.16 MeV) $^{204}$Hg + $^{198}$Pt. We compare our measurements with the predictions of the GRAZING-F, di-nuclear systems (DNS) and improved quantum molecular dynamics (ImQMD) models. For the observed isotopes of the elements Au, Hg, Tl, Pb and Bi, the measured values of the MNT cross sections are orders of magnitude larger than the predicted values. Furthermore, the various models predict the formation of nuclides near the N=126 shell, which are not observed.
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