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

Reaction cross sections with various kinds of breakup channels for neutron-rich carbon isotopes ^18-20C and for ⁹Be 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 ⁴⁰Ar 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 (σR), individual elemental fragmentation cross sections (σΔZ), charge-changing cross sections (σcc), neutron-removal cross sections (σ−xn), and charge-pickup cross sections (σΔZ+1) for ^19,20C; σΔZ, σ−xn, and σΔZ+1 for ¹⁸C; and σR for ⁹Be. The present σR of ⁹Be on proton, σR=397±23 mb, measured in the inverse kinematics, was consistent with the previous measurements using proton beams at different laboratories. The σR of ¹⁹C and ²⁰C on proton were determined to be σR=754±22 mb and σR=791±34 mb, respectively. Taking into account the beam energy and target dependence of σR, the present σR are found to be considerably enhanced compared with those measured at around 1 GeV/nucleon. The σΔZ+1 appears to increase with the mass number of the projectiles, and it significantly contributes to σR in the present energy range. The finite-range optical-limit and few-body Glauber model analyses were performed for σR to study the nuclear matter density distributions and to derive the relative strength of the s-wave components of the valence neutrons in ¹⁹C and ²⁰C. A neutron halo structure of ¹⁹C 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 ¹⁹C and σ−2n of ²⁰C also support the decoupled structures of ¹⁸C +n and ¹⁸C+2n, respectively. The σcc of ¹⁹C and ²⁰C agree with each other within their experimental uncertainties, which might indicate a similar proton density distribution in ¹⁹C and ²⁰C. The σΔZ decreases monotonically without the even-odd effect as the number of removed protons increases.