Studies of bremsstrahlung in thick metallic targets produced by continuous beta particles

Abstract

The total bremsstrahlung (BS) is the sum of ordinary bremsstrahlung (OB) and polarization bremsstrahlung (PB). OB is the process by which the photon is emitted by the electron decelerating in the static field of the target atom. PB is the process by which the photon is emitted by the target as a result of its polarization by incident electron. The first Quantum mechanical cross-section formulae for the elementary process of bremsstrahlung was derived by Sommerfeld (1931) in the non relativistic dipole approximation including retardation for non relativistic electrons without taking accounts the nuclear screening effects. For the relativistic case, by using the Dirac theory in the first order Born approximation Bethe and Heitler (1934) obtained an analytical expression for the OB cross-section. They neglected the coulomb field effects on the wave function of incident and scattering electrons on the nucleus. Elwert (1939) gave the multiplicative coulomb correction factor for Bethe-Heitler OB cross-section. Tseng and Pratt (1971) developed a quantum theory for the bremsstrahlung for relativistic electrons by using screened self consistent field wave function. Pratt et al. (1977) published extensive tables of OB cross-section for Z values between 2 and 92 and incident electron energy between 1 and 2000 keV. Seltzer and Berger (1986) calculated the contribution of electron-electron bremsstrahlung given by Pratt et al. (1977). There have been extensive reviews on the theory of OB given by Koch and Motz (1959), Pratt and Feng (1985), Seltzer and Berger (1985) and Pratt et al. (1995). The idea of polarization bremsstrahlung was first given by Buimistrov and Trakhtenberg (1975, 1977). For non-relativistic electron energies, in the Born approximation Amusia et al. (1985) has described that PB can be added with OB in a stripped atom approximation (SAA). The SAA is efficient for obtaining the BS spectra for photon energies greater than the ionization potential of the outer shell electrons of the target atom.