1g9/2,1f5/2

H. Langevin‐Joliot,J. Van de Wiele, J. Guillot, E. Gerlic, L. Rosier, A. Willis, C. Djalali, M. Morlet, E. Tomasi‐Gustafsson,N. Blasi, S. Micheletti,SY van der Werf

Physical review(2002)

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摘要
Neutron inner hole responses in ${}^{115}\mathrm{Sn}$ and ${}^{119}\mathrm{Sn}$ nuclei have been studied via the $(\stackrel{\ensuremath{\rightarrow}}{d},t)$ reaction at ${E}_{d}=200\mathrm{MeV}$ using a polarized beam with both vector and tensor components. One-step pickup observables corresponding to the overlapping ${1g}_{9/2},$ ${1f}_{5/2},$ and ${1f}_{7/2}$ responses were analyzed between $3\ifmmode^\circ\else\textdegree\fi{}$ and $15\ifmmode^\circ\else\textdegree\fi{}$ via a least square fit procedure up to ${E}_{X}=21.5\mathrm{MeV}$ and 20 MeV in ${}^{115}\mathrm{Sn}$ and ${}^{119}\mathrm{Sn},$ respectively. The relative enhancement of transitions with high total angular momentum j and the strongly characteristic angular distributions of ${j}_{\ensuremath{-}}=l\ensuremath{-}1/2$ versus ${j}_{+}=l+1/2$ vector and tensor analyzing powers allow the extraction for the first time of ${1f}_{5/2}$ and ${1f}_{7/2}$ strength distributions and of new ${1g}_{9/2}$ strength in addition to its previously known main component. The standard DWBA analysis is complemented by a refined analysis taking into account the form factor dependence on excitation energy due to the hole coupling with surface vibrations calculated in the framework of the quasiparticle-phonon coupling model (QPMFF). Residual nucleus spectra were measured, mainly in ${}^{115}\mathrm{Sn},$ up to ${E}_{X}\ensuremath{\sim}45\mathrm{MeV}$ where the underlying background of multistep reactions is dominant and can be calibrated. The background of multistep pickup cross section is calculated for the first time in the forward angle region, assuming a dominant role of collective excitations in inelastic steps. Coupled channel calculations for two-step pickup observables involving low multipole collective excitations are performed for comparison. Integrated strengths deduced in the present work are compared with previous data on the ${1g}_{9/2}$ structure and tail, and with the very limited previous information existing on the $1f$ strengths. The ${1g}_{9/2},$ ${1f}_{5/2},$ and ${1f}_{7/2}$ QPMFF and standard strength distributions are compared with available theoretical predictions. In particular, we find that the ${1f}_{5/2}$ and ${1f}_{7/2}$ strength distributions are not well reproduced by the QPM model. The QPMFF spreading widths are found much narrower than the standard ones, but nevertheless much wider than predicted by theoretical calculations.
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