An explanation for the anomalous wave profiles obtained in Composition B-3 impacted by flat nosed steel rods

When firing flat nosed steel rods into the 60/40 RDX/TNT explosive Composition B-3, Gustavsen et al.(``Initiation of Composition B-3 by impact of flat nosed rods,'' in 15$^{th}$ Int. Det. Symp.) found an apparently anomalous ``hump'' in particle velocity wave profiles. The hump occurred on the center-line established by the rod, and at relatively late times, $>$ 1 $\mu$s, after detonation onset. Several explanations, including that of a late time reaction, were postulated. This report will present evidence that the anomalous late time ``hump'' is due to the arrival of rarefaction waves from the rod periphery. Simple analytic calculations and reactive-burn hydro-code calculations will be presented supporting this hypothesis.