Doubly differential positron-backscattering yields

Abstract

Direct measurements of doubly differential (angle and energy) distributions of backscattered positrons are reported using an electrostatically guided slow-positron beam. Backscattering yields for 35-keV positrons incident normally on the target were measured as a function of both scattering angle 8 and target atomic number Z (4~ZS 82). Absolute backscattering coefficients for positrons are com-

Theory of positrons in solids and on solid surfaces

“…several groups (Massoumi et al , 1991(Massoumi et al , , 1992(Massoumi et al , , 1993Coleman et al , 1992;Makinen, Palko, et al , 1992). Massoumi et al (1991,1992,1993) have measured the energy and angle-resolved probabilities for several elemental solids.…”

Simulation of positron backscattering on Al, Cu, Ag and Au targets using GEANT4 code

“…It is well known that the fraction of the primary positrons from surface can be described by the backscattering coefficient, which is usually used as a major index to characterize the absorbed rate of incident particles and could provide basic mechanism to describe the scattering processes accurately . The dependence of backscattering coefficients for positrons or electrons on target thicknesses, atomic number Z , particle energy and incident angles have been widely investigated . However, most works focused on one certain factor of those mentioned above, and the corresponding backscattering spectra were rarely reported.…”

“…[16] The dependence of backscattering coefficients for positrons or electrons on target thicknesses, atomic number Z, particle energy and incident angles have been widely investigated. [17][18][19][20][21][22][23][24][25] However, most works focused on one certain factor of those mentioned above, and the corresponding backscattering spectra were rarely reported. In experiments, the energy loss spectra of backscattered positrons could be used to characterize the components, morphology and structure of the material surface.…”

Benchmarking EGSnrc in the kilovoltage energy range against experimental measurements of charged particle backscatter coefficients

“…At near-grazing incidence angles, the non-zero diameter of the incident beam can become an issue because it becomes harder to guarantee that all incident charged particles hit the sample (Massoumi et al 1993). Similarly, at near-grazing backscatter angles, and because of the finite solid angle subtended by the detector, a portion of the detector may be masked by the sample itself which leads to under-estimation of η (Massoumi et al 1991). Electrons backscattered from the sample may backscatter again at the face of the detector, or they may completely stop in the detector entrance window (Massoumi et al 1993, Gérard et al 1995.…”