A direct measurement of the total proton decay width of an isobaric analog state

Differential cross sections for the ²⁰⁸Pb (p, n) reaction populating the isobaric analog state (IAS) of the ²⁰⁸Pb ground state in ²⁰⁸Bi have been measured at a proton bombarding energy of 30.5 MeV. The experimental technique utilized the proton (p?) decay of the IAS to obtain neutron time-of-flight spectra. When these differential cross sections are compared to those obtained for the same reaction at 30.5 MeV using the pulsed-beam technique to obtain neutron time-of-flight spectra, the percentage of the IAS decay through p? channels is obtained. This comparison indicates that the p? decay of the IAS to the first three states of ²⁰⁷Pb accounts for almost all of the IAS width (0.97±0.28).