Cross-section for formation of the triplet positron-helium bound state

Sudha Swaminathan

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

Joseph Di Rienzi, Richard J. Drachman

We have previously calculated the cross section for radiative formation of the interesting bound state consisting of a positron bound to helium, where the atomic electrons are in the triplet spin state. That process uses the metastable triplet helium system as target, and, as expected, it has a very small cross section. In this paper we examine a more probable process in which the state of interest is produced in an exchange rearrangement collision between a positronium atom and the singlet helium ground state: $\mathrm{Ps}+\mathrm{He}(^{1}S^{\mathrm{e}})\ensuremath{\rightarrow}\mathrm{Ps}{\mathrm{He}}^{+}(^{3}S^{\mathrm{e}})+{e}^{\ensuremath{-}}$. The present calculation is done in the plane-wave Born approximation, using simple initial and final wave functions and compares post and prior forms.

Richard J. Drachman

Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.

P. Cavaliere, G. Ferrante

Joseph Di Rienzi, Richard J. Drachman

In this study we evaluate the cross section for forming the nonrelativistically bound state of a positron with the helium triplet atom by radiative attachment. Although this cross-section was expected to be small compared with a competing rearrangement process involving positronium and ground-state helium, this calculation is a first step which should be useful for experimental production of this interesting system