Matter radius of Kr78 from proton elastic scattering at 153 MeV

Small-angle differential cross sections of proton elastic scattering off $^{78}\mathrm{Kr}$ with a collision energy of 152.7 MeV/u were measured at the experimental Cooler Storage Ring of the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR). Low energy recoil protons from the elastic scattering were counted by a silicon-strip detector to determine relative differential cross sections. A model-dependent root-mean-square matter radius of 4.16(12) fm for the $^{78}\mathrm{Kr}$ nucleus was deduced by employing the Glauber model. Compared to the proton radius of 4.13 fm for $^{78}\mathrm{Kr}$, our center value of matter radius is slightly larger. This finding in $^{78}\mathrm{Kr}$ is opposite to the known results of $^{76,80}\mathrm{Kr}$, where the matter radii are smaller than the corresponding proton radii. However, considering the relatively large radius error of $^{78}\mathrm{Kr}$, the difference is not statistically significant, and further experiments are necessary.