POSITRONS AND POSITRONIUM IN GRAINY AND POROUS SOLIDS

Zs. Kajcsosa, L. Liszkaya, G. Duplatreb, L. Vargaa, K. Lazarc, G. Pal-Borbelyd, H.K. Beyerd, L. Lohonyaia, P. Caullete and J. Patarine aKFKI Res. Inst. for Part. Nucl. Physics, P.O.B. 49, 1525 Budapest 114, Hungary bLab. Chim. Nucleaire, IReS, IN2P3/CNRS, BP. 28, 67037 Strasbourg Cedex 2, France cInst. of Isotope and Surface Chemistry, P.O.B. 77, 1525 Budapest, Hungary dCentr. Res. Inst. for Chemistry, P.O.B. 19, 1525 Budapest, Hungary eLab. Mat. Mineraux, URA CNRS 428 3 rue A. Werner, 68093 Mulhouse Cedex, France

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Systematic investigations have been performed using positron annihilation techniques on micrograins of crystalline powders (e.g., MgO, Al2O3, SiO2) and on various zeolites (e.g., silicalite 1, Na-X, Na-Y, ZSM-5, mordenite) aiming at a better understanding of the formation and decay of the long-lived ortho-positronium states. The techniques were lifetime spectroscopy, Doppler-effect measurements and the recording of the full energy distribution of the annihilation radiation. The influences of heat treatment, sample evacuation and presence of gases were investigated. Lifetimes over 130 ns and o-Ps fractions of about 30% were found. A strong correlation of positron annihilation technique data with a water content of the samples was evidenced. Possible pictures of the formation and decay of ortho-positronium in porous media are discussed.

DOI: 10.12693/APhysPolA.99.399 PACS numbers: 78.70.Bj, 36.10.Dr, 61.43.Gt