The measurement by Duff and Heymann in 1962 of the pressure-proportional pick-off quenching rate of orthopositronium in helium gas may be interpreted as giving an effective number of electrons per atom in a singlet state relative to the positron of 0 108 ± 0 010 for thermal orthopositronium kinetic energies. A trial wave function used in the study of collisions of orthopositronium with helium, arising from an extension of work by Fraser in 1962, is employed to calculate this effective number of electrons. The unsatisfactory result at low energies is 0.019. A possible improvement in the collision trial wave function is suggested.The measurement by Duff and Heymann in 1962 of the pressure-proportional pick-off quenching rate of orthopositronium in helium gas may be interpreted as giving an effective number of electrons per atom in a singlet state relative to the positron of 0 108 ± 0 010 for thermal orthopositronium kinetic energies. A trial wave function used in the study of collisions of orthopositronium with helium, arising from an extension of work by Fraser in 1962, is employed to calculate this effective number of electrons. The unsatisfactory result at low energies is 0.019. A possible improvement in the collision trial wave function is suggested.

Proceedings of the Physical SocietyNov 1, 196645 citations

POSITRON—ATOM BOUND STATES AND INTERACTIONS

M. W. J. Bromley, Jim Mitroy, S. A. Novikov +2 more

International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC)Nov 1, 20060 citations

Pick-off annihilation in positronium scattering from alkali-metal ions

Igor A. Ivanov, Jim Mitroy

When orthopositronium collides with a closed-shell atom or ion the ``pick-off'' process is the dominant process for positron annihilation. In pick-off annihilation the positron annihilates with electrons in the target but not with the electron that is part of the positronium atom. The rate for pick-off annihilation, expressed in terms of the dimensionless parameter ${}^{1}{Z}_{\mathrm{eff}},$ for orthopositronium scattering from ${\mathrm{Li}}^{+},{\mathrm{Na}}^{+},$ and ${\mathrm{K}}^{+}$ was computed with an ${L}^{2}$ variant of the fixed-core stochastic variational method. The threshold ${}^{1}{Z}_{\mathrm{eff}}$ for ${\mathrm{Li}}^{+}$ and ${\mathrm{Na}}^{+},$ which can form a stable bound state with Ps were found to be 0.067 and 0.73, respectively, while that for ${\mathrm{K}}^{+},$ which does not bind Ps, was 0.064.When orthopositronium collides with a closed-shell atom or ion the ``pick-off'' process is the dominant process for positron annihilation. In pick-off annihilation the positron annihilates with electrons in the target but not with the electron that is part of the positronium atom. The rate for pick-off annihilation, expressed in terms of the dimensionless parameter ${}^{1}{Z}_{\mathrm{eff}},$ for orthopositronium scattering from ${\mathrm{Li}}^{+},{\mathrm{Na}}^{+},$ and ${\mathrm{K}}^{+}$ was computed with an ${L}^{2}$ variant of the fixed-core stochastic variational method. The threshold ${}^{1}{Z}_{\mathrm{eff}}$ for ${\mathrm{Li}}^{+}$ and ${\mathrm{Na}}^{+},$ which can form a stable bound state with Ps were found to be 0.067 and 0.73, respectively, while that for ${\mathrm{K}}^{+},$ which does not bind Ps, was 0.064.

Physical Review AMar 1, 20029 citations

Positronium-ion spin states in the scattering of polarized orthopositronium

Sudha Swaminathan

Abstract A single rearrangement collision between two spin-polarized orthopositronium beams leading to the production of either negative or positive positronium ions is studied. Negative or positive ions can be produced by the attachment of an electron or positron to a positronium atom, respectively. The probabilities for the formation of all possible spin states for both types of positronium ions are determined. The spin scattering matrix constructed using angular-momentum coupling as well as the spin density matrix containing the probabilities are given. The probabilities depend on the angle between the polarization vectors of the incoming beams and the real parts of complex scattering amplitudes labeled with total electron and total positron spin. We describe the effect of the spin alignment between the two beams on the probabilities and how the annihilation rates for ion decay and the real parts of the amplitudes can be obtained.Abstract A single rearrangement collision between two spin-polarized orthopositronium beams leading to the production of either negative or positive positronium ions is studied. Negative or positive ions can be produced by the attachment of an electron or positron to a positronium atom, respectively. The probabilities for the formation of all possible spin states for both types of positronium ions are determined. The spin scattering matrix constructed using angular-momentum coupling as well as the spin density matrix containing the probabilities are given. The probabilities depend on the angle between the polarization vectors of the incoming beams and the real parts of complex scattering amplitudes labeled with total electron and total positron spin. We describe the effect of the spin alignment between the two beams on the probabilities and how the annihilation rates for ion decay and the real parts of the amplitudes can be obtained.

Journal of Physics B Atomic Molecular and Optical PhysicsSep 9, 20260 citations

Antiproton Helium Polarization States

Jaume Carbonell, F. Ciesielski, Claude Gignoux

Few-body systems. SupplementumJan 1, 19954 citations

{}^{1}{Z}_{\mathrm{eff}},

for orthopositronium scattering from

{\mathrm{Li}}^{+},{\mathrm{Na}}^{+},

and

{\mathrm{K}}^{+}

was computed with an

{L}^{2}

variant of the fixed-core stochastic variational method. The threshold

{}^{1}{Z}_{\mathrm{eff}}

for

{\mathrm{Li}}^{+}

and

{\mathrm{Na}}^{+},

which can form a stable bound state with Ps were found to be 0.067 and 0.73, respectively, while that for

{\mathrm{K}}^{+},

which does not bind Ps, was 0.064.