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A search for the J π = 1/2 − spin-orbit partner of the J π = 3/2 − ground state in 7 He has been performed with the 7 Li(d, 2 He) chargeexchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on 7 Li as well as on triton and 4 He clusters in the 7 Li ground state. A possible resonance at an excitation energy E x ≈ 1.45 MeV with a width Γ ≈ 2.0 MeV is suggested when the quasifree charge-exchange process on 7 Li is constrained by a measurement of the 6 Li(d, 2 He) reaction. Gamow-Teller strengths for transitions to the lowest states in 7 He deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations.

Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number A ¼ 42, 46, 50, and 54 "f-shell" nuclei in ( 3 He, t) charge-exchange reactions. In the 42 Ca → 42 Sc reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As A increases, a high-energy GT phonon excitation develops in the 6-11 MeV region. In the 54 Fe → 54 Co reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei.

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