Exclusive cross sections and momentum distributions have been measured for quasifree one-neutron knockout reactions from a 54 Ca beam striking on a liquid hydrogen target at ∼200 MeV=u. A significantly larger cross section to the p 3=2 state compared to the f 5=2 state observed in the excitation of 53 Ca provides direct evidence for the nature of the N ¼ 34 shell closure. This finding corroborates the arising of a new shell closure in neutron-rich calcium isotopes. The distorted-wave impulse approximation reaction formalism with shell model calculations using the effective GXPF1Bs interaction and ab initio calculations concur our experimental findings. Obtained transverse and parallel momentum distributions demonstrate the sensitivity of quasifree one-neutron knockout in inverse kinematics on a thick liquid hydrogen target with the reaction vertex reconstructed to final state spin-parity assignments.
Background: Deuteron-induced one-neutron transfer reactions have been used to extract single-particle properties of nuclei, and the adiabatic (AD) approximation is often used to simply treat the deuteron breakup states. Purpose: The primary goal is to examine the validity of the AD approximation for the (d, p) reaction systematically. We clarify also the role of the closed channels often ignored in the description of breakup reactions. Methods: We calculate the (d, p) cross sections with the continuum-discretized coupled-channels method (CDCC) for 128 reaction systems and compare the results with those obtained by the CDCC calculation with the AD approximation. Effect of the closed channels are investigated by ignoring them in CDCC. Results: The AD approximation affects in general the (d, p) cross section by less than 20 %, but some exceptional (nonadiabatic) cases for which the AD approximation breaks down are found. The closed channels turn out to give significant effects on the cross section at deuteron energies less than about 10 MeV. Conclusions: The use of the AD approximation in the description of the (d, p) reaction can be justified in many cases, with the uncertainty of less than about 20 %. The existence of some nonadiabatic cases nevertheless should be realized. The neglect of the closed channels without confirming the convergence of the CDCC result is not recommended. 24.10.Eq, 25.45.Hi
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