Nuclear reactions of 19,20C on a liquid hydrogen target measured with the superconducting TOF spectrometer

Abstract Reaction cross sections with various kinds of breakup channels for neutron-rich carbon isotopes 18–20 C and for 9 Be impinging on a liquid hydrogen target were investigated at 40 MeV/nucleon. The nuclides of interest were produced via projectile fragmentation from a 63 MeV/nucleon 40 Ar beam and were separated in flight at the RIKEN projectile fragment separator (RIPS). The combination of the large-acceptance superconducting TOF spectrometer, TOMBEE (TOF Mass analyzer for exotic BEam Experiment), with a liquid hydrogen target, CRYPTA (CRYogenic ProTon and Alpha target system), enables simultaneous measurements of several reaction channels: the reaction cross sections ( σ R ), individual elemental fragmentation cross sections ( σ Δ Z ), charge-changing cross sections ( σ cc ), neutron-removal cross sections ( σ − x n ), and charge-pickup cross sections ( σ Δ Z + 1 ) for 19,20 C; σ Δ Z , σ − x n , and σ Δ Z + 1 for 18 C; and σ R for 9 Be. The present σ R of 9 Be on proton, σ R = 397 ± 23 mb , measured in the inverse kinematics, was consistent with the previous measurements using proton beams at different laboratories. The σ R of 19 C and 20 C on proton were determined to be σ R = 754 ± 22 mb and σ R = 791 ± 34 mb , respectively. Taking into account the beam energy and target dependence of σ R , the present σ R are found to be considerably enhanced compared with those measured at around 1 GeV/nucleon. The σ Δ Z + 1 appears to increase with the mass number of the projectiles, and it significantly contributes to σ R in the present energy range. The finite-range optical-limit and few-body Glauber model analyses were performed for σ R to study the nuclear matter density distributions and to derive the relative strength of the s -wave components of the valence neutrons in 19 C and 20 C. A neutron halo structure of 19 C is confirmed with an s -wave dominance of the valence neutron when the effect of the charge-pickup reaction is taken into account. The large σ − n of 19 C and σ − 2 n of 20 C also support the decoupled structures of 18 C + n and 18 C + 2 n , respectively. The σ cc of 19 C and 20 C agree with each other within their experimental uncertainties, which might indicate a similar proton density distribution in 19 C and 20 C. The σ Δ Z decreases monotonically without the even–odd effect as the number of removed protons increases.