Umklapp Annihilation of Positronium in Crystals

Abstract

Previous experiments with positron annihilation in single crystals of quartz have revealed an interesting series of narrow peaks on the momentum distribution of the annihilation photons. Our experiments repeat these observations and also confirm that no very long lifetime exists. We outline a simple theoretical model based upon the necessity of treating the positronium electron and the remaining electrons in the crystal as indistinguishable. The model yields results compatible with both momentum and lifetime data.

Direct Measurement of the Parapositronium Lifetime inα−SiO2

“…Positronium (Ps) in -SiO 2 has been of continued interest for more than three decades [1][2][3][4][5][6][7][8][9][10][11][12][13] ever since Brandt et al identified the delocalized Ps state in the angular correlation of the annihilation radiation (ACAR) spectrum [2]. Ps can exist in either a spin singlet (para) state or a spin triplet (ortho) state.…”

Anisotropic Magnetic Quenching of Positronium Formed by Polarized Positrons in Oriented Crystals

“…These parameters were obtained beforehand by fitting the ACAR experimental data for the X-orientation of the quartz sample [10]. The results of the fit are α = 0.84 (in agreement with [11,13]; see, however [14,15] The magnetic quenching parameter for "anomalous Ps" in naphthalene single crystal can be obtained from that for "normal Ps" in noncubic inorganic crystal. One should only change the quadrupole coupling parameters d and η in Eq.…”

“…The magnetic quenching parameter for "normal Ps" in noncubic crystal is of the form [3]: Quasi-Ps in crystalline quartz is reported to be delocalized [10][11][12]. Therefore, it is natural to assume that η = 0.…”

Quadrupole Interactions and Anisotropic Magnetic Quenching of Positronium in Oriented Crystals

“…Ps in α-quartz is observed to be delocalized in a wide temperature range from 88 to 684 K [14,15]. This is similar, to some extent, to the fast Mu diffusion at elevated temperatures.…”