In the present work we report on our experimental total cross section and positronium formation cross-section results for positron scattering from pyrimidine for energies from 1 to 180 eV. In addition, the total inelastic integral cross sections (for electronic excitations plus direct ionization) have been measured up to 21.5 eV. We also report quasi-elastic total and differential cross sections at energies up to 21.5 eV. Our results are compared to recent theoretical and experimental data for positron scattering, as well as recent work on electron scattering from this target.
Measurements of the grand total and total positronium formation cross sections for positron scattering from uracil have been performed for energies between 1 and 180 eV, using a trap-based beam apparatus. Angular, quasi-elastic differential cross section measurements at 1, 3, 5, 10, and 20 eV are also presented and discussed. These measurements are compared to existing experimental results and theoretical calculations, including our own calculations using a variant of the independent atom approach.
Recent calculations by Bromley et al. [Phys. Rev. Lett. 109, 063201 (2012)] have indicated that the He(2s 2 1 S e ) state will bind a positron. The e + He(2s 2 1 S e ) state has a binding energy of 0.447 eV with respect to the He(2s 2 1 S e ) state. Binding of a positron to the He 2s 2 state has been predicted to give rise to two resonances in positron scattering from ground-state helium: e + He(2s 2 1 S e ) at 57.3716 eV and a 2 P o shape resonance just above the He(2s 2 1 S e ) threshold at 57.8485 eV. To investigate these predicted resonances, low-energy positron scattering experiments were performed to measure the total and positronium cross sections in the doubly excited region of helium in this energy region. No experimental evidence has been found for these resonances, but upper bounds on the resonance strength were determined for both predicted resonances.
Absolute measurements of elastic differential cross sections for positron scattering from argon at energies from 2-50 eV are presented as well as total elastic and total inelastic cross sections from 2-20 eV. Comparisons of the current data, previous experimental data, and theoretical models using the convergent close-coupling and relativistic optical potential methods are made.
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