Thick-target double bremsstrahlung

Abstract

The measurement of a two-photon coincidence rate obtained when thick foils of silver, gold, and lead are bombarded with the 84- and 88-keV electron from a $\sp{109}$Cd source, has suggested a model based on a thick-target double bremsstrahlung (TTDB) effect. This model has been constructed by integrating approximate DB cross sections over the thickness of the target, taking into account the energy loss of the electron as well as the attenuation of the radiated photons with the target depth. When applied to the geometry of the recent DB experiment of Altman and Quarles (1985)*, the TTDB model has removed the two-order-of-magnitude discrepancy with theory observed in the measurement of the differential cross section of the DB process. The observed enhancement in the measured two-photon yield has been interpreted in terms of a TTDB effect originating in the thick Mylar windows. The results obtained in this work indirectly support the available DB cross section calculations upon which the TTDB model has been based. However, the poor experimental statistics have not allowed a detailed energy dependence of the thick-target effect. Nonetheless, this effect provides interesting possibilities toward the measurement of the fundamental DB cross section. ftn*J. C. Altman and C. A. Quarles, Phys. Rev. A31, 2744 (1985).