NEW DEVELOPMENTS IN THE THEORY OF BREMSSTRAHLUNG

We discuss new progress in bremsstrahlung, beyond the predictions prev iously available. A relativistic code for the calculation of bremsstra hlung in a screened central potential, utilizing an expansion in elect ron partial waves and photon multipoles, was developed some time ago b y Tseng and Pratt [Phys. Rev. A 3 (1971) 100]. For electron bremsstrah lung, unlike for bremsstrahlung in ion-atom collisions, this potential bremsstrahlung contribution generally dominates the atomic or polariz ational bremsstrahlung contribution associated with atomic structure, except for radiation of energies comparable to transition energies [M. Y. Amusia and R.H. Pratt, Commun. At. Mel. Phys. 28 (1992) 247]. Predi ctions from the potential bremsstrahlung calculations are in reasonabl y good agreement with experiment [R.H. Pratt and I.-J. Feng, in: Atomi c Inner Shell Physics, ed. B. Crasemann (Plenum, New York, 1985) p.]. Tabulations are available for both the spectrum and the bremsstrahlung angular distribution [R.H. Pratt, Atom. Data Nucl. Data Tables 20 (19 77) 175; L.D. Kissel et al., ibid. 28 (1983) 381]. A major shortcoming has been that the code only obtains the doubly differential cross sec tion, summing over all states of the outgoing scattered electron. No a dequate predictions have been available to compare with experimental r esults for the triply differential cross section, which show substanti al disagreement with simpler theory [W. Nakel, in press, 1994]. This p roblem has recently been remedied [X.M. Tong, C.D. Shaffer and R.H. Pr att, to be published], directly summing numerically the partial wave c ontributions to the matrix element. In the first cases studied good ag reement has been achieved with the experiments. A second shortcoming o f the code was its inability to deal with incident electron energies b elow about 1 KeV, needed to study the transition between classical and quantum behavior [L. Kim and R.H. Pratt, Phys. Rev. A 36 (1987) 45]. We discuss recent results in this classical domain. We also review new developments in polarizational bremsstrahlung and two photon bremsstr ahlung.