ELECTRON-POSITRON INTERACTION IN AROMATIC CRYSTALS

Electron-positron annihilation spectra obtained from Doppler broadening of 511 keV radiation for hexamethylbenzene (HMB), hexachlorobenzene (HCB) and 2,3-dichloro-9,10-anthraquinone (DCAQ) crystals reveal anisotropic electron momentum distribution, the momentum along the molecular planes being lower than the momentum along the other direction. Positronium is formed in HMB, HCB, and the complexes of durene with trinitrobenzene (TNB), p-chloranil and p-bromanil, but not in DCAQ, anthracene, 9,10-anthraquinone, p-chloranil, nor in the complexes of anthracene with TNB and pyromellitic dianhydride in the solid state.