Resonant proton scattering on 46Ar using the Active-Target Time Projection Chamber

A well-known technique for studying the single-particle properties of neutron-rich nuclei is to use resonant proton scattering on a parent nucleus to populate the isobaric analog states of the corresponding neutron-rich nucleus. The locations and amplitudes of these resonances are directly related to the structure of the nucleus of interest by isospin symmetry. We performed an experiment of this type at the National Superconducting Cyclotron Laboratory to commission the recently completed Active-Target Time Projection Chamber (AT-TPC). A 4.6-MeV/u radioactive beam of 46Ar was injected into the AT-TPC. The detector was filled with isobutane gas---which provided the protons for the reaction and served as the tracking medium---and placed inside a 2-T magnetic field. We will present preliminary results from this experiment and discuss the benefits of the active-target method for this type of measurement.