High-resolution study of Gamow-Teller excitations in theCa42(He3,t)

Y. Fujita et al.; 15 pags.; 6 figs.; 7 tabs.; PACS number(s): 21.10.Hw, 25.55.Kr, 27.40.+z, 25.40.Ep© 2015 American Physical Society. To study the Gamow-Teller (GT) transitions from the Tz=+1 nucleus Ca42 to the Tz=0 nucleus Sc42, where Tz is the z component of isospin T, we performed a (p,n)-type (He3,t) charge-exchange reaction at 140 MeV/nucleon and scattering angles around 0. With an energy resolution of 29 keV, states excited by GT transitions (GT states) could be studied accurately. The reduced GT transition strengths B(GT) were derived up to the excitation energy of 13 MeV, assuming the proportionality between the cross sections at 0 and B(GT) values. The main part of the observed GT transition strength is concentrated in the lowest 0.611-MeV, Jπ=1+ GT state. All the other states at higher energies are weakly excited. Shell-model calculations could reproduce the gross feature of the experimental B(GT) distribution, and random-phase-approximation calculations including an attractive isoscalar interaction showed that the 0.611-MeV state has a collective nature. It was found that this state has all of the properties of a >low-energy super-Gamow-Teller state.> It is expected that low-lying Jπ=1+ GT states have T=0 in the Tz=0 nucleus Sc42. However, T=1 states are situated in a higher energy region. Assuming an isospin-analogous structure in A=42 isobars, analogous T=1, 1+ states are also expected in Ca42. Comparing the Ca42(He3,t)Sc42 and Ca42(p,p′) spectra measured at 0, candidates for T=1 GT states could be found in the 10-12-MeV region of Sc42. They were all weakly excited. The mass dependence of the GT strength distributions in Sc isotopes is also discussed.Y.F. also acknowledges the support of MEXT, Japan under\udGrants No. 18540270, No. 22540310, and No. 15K05104.\udY.F. and B.R. are grateful for the support of the Japan-Spain\udcollaboration program by JSPS and CSIC; A.A., E.E.A., and\udB.R. are thankful for the support of Spanish Ministry under\udGrants No. FPA2005-03993, No. FPA2008-06419-C02-01,\udand No. FPA2011-24553. G.S. acknowledges the support of\udTUBITAK, Turkey under Research Scholarship No. BIDEB\ud2214. J.M.D., C.J.G., R.M., G.P., and R.G.T.Z. are grateful for\udthe support of the US NSF under Grants No. PHY-0606007 and\udNo. PHY-0822648 (JINA). M.C., J.G., and A.K. acknowledge\udthe support of the OTKA Foundation, Hungary, under Grant\udNo. K106035. This work was in part supported by the RIKENCNS\udjoint research project on large-scale nuclear-structure\udcalculations.Peer Reviewe