First Nuclear Self-Absorption Experiment at HI$\gamma$S Relevant to Astrophysics

In supernovae explosion, about 35 nuclei cannot be produced by $r$ or $s$ processes. These co-called $p$ nuclei can be created by photodisintegration reactions only. Furthermore, network calculations underpredict the abundances of the $p$ nuclei which require more precise measurements of the photo-induced reactions. The accuracy of those measurements rely on the uncertainty of the width of the levels in $^{11}$B used as a calibration standard. These are currently known with a relative uncertainty not better than 5\%. We report the results for the width of the levels at $7.285$ and $8.920$ MeV in $^{11}$B from the first nuclear self-absorption experiment at the High Intensity $\gamma$-Ray Source Facility at Triangle Universities Nuclear Laboratory using monoenergetic photon beams.