Spectroscopy of 17C via one-neutron knockout reaction

Abstract

The great interest in unique features of the neutron-rich nuclei which are anticipated to play a key role in the neutron capture processes has heightened the need for experimental investigation of the nuclear properties such as masses, lifetimes, and reaction rates. In the present work, we focus on the measurement of excited states in 17C and the assignment of their spin-parities (Jπ).

The low-lying excited states of 17C below the neutron separation energy have been well established with de?nite Jπ [1]. For unbound states of 17C, however, a few experiments have been carried out. Negative parity states were found at the excitation energies (Ex) of 2.71(2), 3.93(2), and 4.05(2) MeV with Jπ = 1/2?, 3/2?, and (5/2?), respectively, by β-delayed neutron measurement [2] while positive parity states were observed at Ex = 2.20(3), 3.05(3), and 6.13(9) MeV with Jπ = 7/2+, 9/2+, and 5/2+, respectively, by proton inelastic scattering [3].

In this measurement, the spectroscopy of 17C was conducted via one-neutron knockout reaction capable of removing an inner neutron with a large momentum transfer and large cross section. The nucleon knockout reaction allows us to derive the orbital angular momentum of the removal nucleon by comparison of the parallel or the transverse momentum distributions between the data and the model calculation. The experiment was performed during the first physics runs of SAMURAI spectrometer [4] at RIBF in RIKEN. By one-neutron knockout reaction of 18C on a carbon target, three unbound states at the excitation energies (Ex) of 2.66(2), 3.16(5), and 3.97(3) MeV and a bound state at Ex = 321.3(18) keV in 17C were measured. To determine the orbital angular momenta (L) of them, the parallel and transverse momentum distributions were illustrated and compared with calculated distributions. As the results, two unbound states at Ex = 2.66(2) and 3.97(3) MeV were confirmed as L = 1 while the bound state was well described by the calculated distribution of L = 2. For the unbound state at Ex = 3.16(5) MeV, Jπ was assigned as 9/2+ state by the calculation of the decay width.

[1]Y. Kondo et al.: Phys. Rev. C 79 (2009) 014602. [2]H. Ueno et al.: Phys. Rev. C 87 (2013) 034316. [3]Y. Satou et al.: Phys. Lett. B 660 (2008) 320. [4]T. Kobayashi et al.: Nucl. Instrum. Methods Phys. Res., Sect. B 317 (2013) 294.