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Register a new user${}^{7}$Li($d$,$p$)${}^{8}$Li transfer reaction in the NCSM/RGM approach
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Recently, we applied an $ab$ $initio$ method, the no-core shell model combined with the resonating group method, to the transfer reactions with light p-shell nuclei as targets and deuteron as the projectile. In particular, we studied the elastic scattering of deuterium on $^7$Li and the ${}^{7}$Li($d$,$p$)${}^{8}$Li transfer reaction starting from a realistic two-nucleon interaction. In this contribution, we review of our main results on the ${}^{7}$Li($d$,$p$)${}^{8}$Li transfer reaction, and we extend the study of the relevant reaction channels, by showing the dominant resonant phase shifts of the scattering matrix. We assess also the impact of the polarization effects of the deuteron below the breakup on the positive-parity resonant states in the reaction. For this purpose, we perform an analysis of the convergence trend of the phase and eigenphase shifts, with respect to the number of deuteron pseudostates included in the model space.
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The relative importance of neutron transfer and breakup process in reaction around Coulomb barrier energies have been studied for the $^{7}$Li+$^{124}$Sn system. Coupled channel calculations have been performed to understand the one neutron stripping and pickup cross sections along with the breakup in the $^{7}$Li+$^{124}$Sn system. The systematics of one and two neutron striping and pickup cross sections with $^7$Li projectile on several targets show an approximate universal behaviour that have been explained by a simple model. Complete reaction mechanism have been studied by comparing the reaction cross sections with cumulative cross sections of total fusion and one neutron transfer.
The $^8$Li($n,gamma$)$^9$Li reaction plays an important role in several astrophysics scenarios. It cannot be measured directly and indirect experiments have so far provided only cross section limits. Theoretical predictions differ by an order of magnitude. In this work we study the properties of $^9$Li bound states and low-lying resonances and calculate the $^8$Li($n,gamma$)$^9$Li cross section within the no-core shell model with continuum (NCSMC) with chiral nucleon-nucleon and three-nucleon interactions as the only input. The NCSMC is an ab initio method applicable to light nuclei that provides a unified description of bound and scattering states well suited to calculate low-energy nuclear scattering and reactions. Our calculations reproduce the experimentally known bound states as well as the lowest $5/2^-$ resonance of $^9$Li. We predict a $3/2^-$ spin-parity assignment for the resonance observed at 5.38 MeV. In addition to the a very narrow $7/2^-$ resonance corresponding presumably to the experimental 6.43 MeV state, we find several other broad low-lying resonances. Our calculated $^8$Li($n,gamma$)$^9$Li cross section is within the limits derived from the 1998 National Superconducting Cyclotron Laboratory Coulomb-dissociation experiment [Phys. Rev. C {bf 57}, 959 (1998)]. However, it is higher than cross sections obtained in recent phenomenological studies. It is dominated by a direct E1 capture to the ground state with a resonant contribution at $sim0.2$ MeV due to E2/M1 radiation enhanced by the $5/2^-$ resonance.
The p( uc{11}{Li}, uc{9}{Li})t reaction has been studied for the first time at an incident energy of 3$A$ MeV delivered by the new ISAC-2 facility at TRIUMF. An active target detector MAYA, build at GANIL, was used for the measurement. The differential cross sectionshave been determined for transitions to the uc{9}{Li} ground andthe first excited states in a wide range of scattering angles. Multistep transfer calculations using different uc{11}{Li} model wave functions, shows that wave functions with strong correlations between the halo neutrons are the most successful in reproducing the observation.
At the long-wavelength approximation, $E1$ transitions are forbidden between isospin-zero states. Hence $E1$ radiative capture is strongly hindered in reactions involving $N = Z$ nuclei but the $E1$ astrophysical $S$ factor may remain comparable to, or larger than, the $E2$ one. Theoretical expressions of the isoscalar and isovector contributions to $E1$ capture are analyzed in microscopic and three-body approaches in the context of the $alpha(d,gamma)^6$Li reaction. The lowest non-vanishing terms of the operators are derived and the dominant contributions to matrix elements are discussed. The astrophysical $S$ factor computed with some of these contributions in a three-body $alpha+n+p$ model is in agreement with the recent low-energy experimental data of the LUNA collaboration. This confirms that a correct treatment of the isovector $E1$ transitions involving small isospin-one admixtures in the wave functions should be able to provide an explanation of the data without adjustable parameter. The exact-masses prescription which is often used to avoid the disappearance of the $E1$ matrix element in potential models is not founded at the microscopic level and should not be used for such reactions. The importance of capture components from an initial $S$ scattering wave is also discussed.
The cross section for the reaction $p+^6text{Li}toeta+^7text{Be}$ was measured at an excess energy of 11.28 MeV above threshold by detecting the recoiling $^7$Be nuclei. A dedicated set of focal plane detectors was built for the magnetic spectrograph Big Karl and was used for identification and four momentum measurement of the $^7$Be. A differential cross section of $frac{dsigma}{dOmega}=(0.69pm{0.20}text{(stat.)}pm 0.20text{(syst.)})text{nb/sr}$ for the ground state plus the 1/2$^-$ was measured. The result is compared to model calculations.
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