Reaction cross section ${\sigma }_R$ of proton-rich isotones $\mathrm{}(N=10\mathrm{})\mathrm{}$ near ${}^{23}\mathrm{Al}$ and Al isotopes ${(}^{23-28}\mathrm{Al})$ on C target have been measured at intermediate energies around 30 MeV/nucleon. An abnormal increase of the experimental ${\sigma }_R$ is observed for ${}^{23}\mathrm{Al}$ and it suggests that there is an anomalously large matter rms radius in ${}^{23}\mathrm{Al}.$ Together with the very weakly binding of the last proton ${(S}_p=0.125\mathrm{}\hspace{0.5em}\mathrm{MeV}),$ it indicates that there is a proton halo in ${}^{23}\mathrm{Al}.$ This conclusion is also supported by the difference factor d which is deduced from the measured and theoretical ${\sigma }_R$ in the Glauber or Boltzmann-Uehling-Uhlenbeck model and is used for the manifest of halo phenomena. The theoretical calculation based on the relativistic density dependent Hartree model shows that there is a proton halo when the last proton is in the ${2s}_{1/2}$ orbit in ${}^{23}\mathrm{Al}.$ The significance of the proton halo in ${}^{23}\mathrm{Al}$ is discussed.

• Received 21 June 2001

DOI:https://doi.org/10.1103/PhysRevC.65.024610