Two-neutron removal cross sections from ${}^{15,16}\mathrm{C}$ at around 240 MeV/nucleon

The cross sections for two-neutron removal from ${}^{15,16}\mathrm{C}$ on a carbon target have been measured at around 240 MeV/nucleon. The measured cross section for ${}^{15}\mathrm{C}$ is smaller than for ${}^{16}\mathrm{C}$. The trends of the cross sections for ${}^{15,16}\mathrm{C}$ are inconsistent with the previously reported experimental data, but in agreement with the theoretical predictions based on eikonal-model calculations. Based on the present results of ${}^{15,16}\mathrm{C}$ combined with the available experimental data on ${}^{17–20}\mathrm{C}$, an odd-even staggering of the two-neutron removal cross sections along the neutron-rich carbon isotopic chain from ${}^{15}\mathrm{C}$ to ${}^{20}\mathrm{C}$ is observed, and this feature is well reproduced by the theoretical calculations.

Figure 1

Schematic view of the layout of (a) RIBLL2 and (b) ETF.

Figure 2

The particle identification spectra for the incoming (a) ${}^{15}\mathrm{C}$ and (b) ${}^{16}\mathrm{C}$ beams.

Figure 3

The mass number $A$ identification spectra of the particles after the reaction target for (a) ${}^{15}\mathrm{C}$ and (b) ${}^{16}\mathrm{C}$ incident beams. The particles are already charge selected for $Z=6$.

Figure 4

Measured and calculated two-neutron removal cross sections for carbon isotopes. The solid line joins the measured cross sections of the present work for ${}^{15,16}\mathrm{C}$ (red solid squares) and other work for ${}^{17–20}\mathrm{C}$ (black solid circles) [8, 9, 10, 11]. The measured cross sections for ${}^{15,16}\mathrm{C}$ in Refs. [12, 13] are also shown by solid circles. The dashed line joins the calculated results from Refs. [7, 8]. The dotted line connects the calculated results for ${}^{15,16}\mathrm{C}$ at 240 MeV/nucleon.