There is a need to calculate loss rates when trapped Van Allen radiation encounters inert orbiting material such as planetary rings and satellites. An analytic expression for the probability of a hit in a bounce encounter is available for all cases where the absorber is spherical and the particles are gyrotropically distributed on a cylindrical flux tube. The hit probability is a function of the particle's pitch angle, the size of the absorber, and the distance between the flux tube and the absorber when distances are scaled to the gyroradius of a particle moving perpendicular to the magnetic field. Using this expression, we have computed hit probabilities in drift encounters for all regimes of particle energies and absorber sizes. This technique generalizes our approach to sweeping lifetimes and is particularly suitable for attacking the inverse problem, where one is given a sweeping signature and wants to deduce the properties of the absorber(s). ¿ American Geophysical Union 1988