Crosscorrelations of solar Lyman &agr; and cosmic ray data from 1981 until 1990 recorded by instruments on Pioneer 10 during its interplanetary cruise are presented. Using the Lyman &agr; radiation as a proxy for the long-term solar activity, a comparison of the correlation functions of the anomalous and galactic cosmic ray data reveals a significantly greater phase shift in the time variation of the former. This additional time lag is increasing with increasing particle energy and is attributed to the time required to energize pickup ions at the heliospheric termination shock and thus allows a determination of the characteristic acceleration time of anomalous cosmic rays. This, in turn, results in an estimate of the efficiency of spatial diffusion of energetic particles perpendicular to the magnetic field just upstream of the heliospheric termination shock at low heliographic latitudes. ¿ 1998 American Geophysical Union