The most neutron-rich carbon isotope 22C has drawn considerable attention due to its possible enhanced halo structure, as suggested by the huge interaction cross section (1.338 ± 0.274 b) on a proton target at 40 MeV/nucleon . The estimated root-mean-squared matter radius of 5.4 ± 0.9 fm is much larger than known halo nuclei such as 11Li. Due to the large uncertainties in both of the interaction cross section and the estimated matter radius of the previous measurement, it has been difficult to drawn definite picture of the halo structure through comparison with theoretical predictions. Therefore, more precise data for of 22C were desired.
With this motivation, the interaction cross sections of the neutron-rich carbon isotopes 19,20,22C on a carbon target at around 250 MeV/nucleon have been measured by using SAMURAI at RIBF. The root-mean squared radius of 22C was deduced by analyzing the present interaction cross section with a four-body (three-body projectile plus target) Glauber reaction model. The extracted value is about 2σ smaller than the previous estimate (5.4 ± 0.9 fm), while it has 7 times smaller uncertainty.
We will present the details of the experiment and discuss the extracted root-mean-squared radius of 22C along with those measured for 19C and 20C.
 K. Tanaka et al., Phys. Rev. Lett. 104, 062701 (2010).