Positrons and Positronium

The prompt photon associated with the emission of the positron is used to trigger a timing circuit. It was found that the appearance of the annihilation photons occurred after a certain delay time. This led to the model that before annihilation. 

Aubert, B., Colas, J., Dobrzynski, L., Ghez, R, Kryn, D., Lacotte, J. C., Mansoulie, B., Mendiburu, J. R, Pripstein, M., Salin, R, and Teiger, J., Saturation of ionization signals in TMP and TMSi at different angles and electric fields, Nucl Instrum. Methods, A286, 147, 1990. 

Bartczak, W. M. and Hummel, A., Computer simulation study of spatial distribution of the ions and electrons in tracks of high energy electrons and the effect on charge recombination, /. Phys. Chem., 97,1253,1993. 

Theory and Practice of Scintillation Counting, Pergamon Press, Elmsford, NY, 1964. 

Mathieu, J., and Torres, L., Relation entre les courbes characteristiques des chambres d ionisation remplies d hexane liquide et I ionisation specifique du rayonnement incin-dent. Application possible a la mesure du facteur de qualite d un rayonnement complexe, Nucl Instrum. Methods, 27, 353,1964. 

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Schrader, D. M. Jean, Y. C. 1988. Positron and Positronium Chemistry. Elsevier, Amsterdam, The Netherlands. 

The physical basis of the interactions of positrons and positronium with atoms and molecules... 

Proceedings of the International Workshop on Low Energy Positron and Positronium Physics (held at Nottingham, UK, 1997) edited by H.H. Andersen, E.A.G. Armour, J.W. Humberston and G. Laricchia, published in Nuclear Instruments and Methods in Physics Research, Section B 143 (1998)... 

Proceedings of the International Workshop on Positron and Positronium Chemistry edited by D.M. Schrader and Y.C. Jean, Elsevier Science, Amsterdam (1988)... 

Proceedings of the Fourth International Workshop on Positron and Positronium Chemistry (held at Le Mont Saint-Odile, France, 1993) edited by I. Billard, G. Duplatre and J.Ch. Abbe, published in Journal de Physique IV, Coll. C4, supp. Journal de Physique II 3 (1993)... 

Goldanskii, V.I. (1968). Physical chemistry of the positron and positronium. Atomic Energy Review 6 3—148. 

Iakubov, I.T. and Khrapak, A.G. (1982). Self-trapped states of positrons and positronium in dense gases and liquids. Rep. Prog. Phys. 45 697-751. 

Laricchia, G. (1995a). Positron and positronium collisions. Nuc. Inst. Meth. B 99 363-367. 

Miller, B.N., Reese, T.L. and Worrell, G.A. (1996). Virial expansion of the positron and positronium decay rate in a dilute gas the linear contribution. 

Ryzhikh, G., Mitroy, J. and Varga, K. (1998b). The structure of exotic atoms containing positrons and positronium. J. Phys. B At. Mol. Opt. Phys. 31 3965-3996. 

The p-Ps has a shorter lifetime than o-Ps and it annihilates into two photons, while o-Ps annihilates into three photons. The intrinsic lifetime is 0.125 ns and 142 ns for the free p-Ps and o-Ps, respectively. In ordinary molecular media, the electron density is low enough so that Ps can pick off electrons from the media that have anti-parallel spin to that of the positron, and undergo two-photon annihilation. This is called the pick-off annihilation of Ps. The pick-off annihilation of o-Ps not only occurs in the form of two-photon annihilation, it also shortens the o-Ps lifetime from 142 ns (free o-Ps) to a few ns. The pick-off annihilation lifetime of o-Ps in molecular systems is about one order of magnitude greater than in crystalline or metallic media. Experimental determination of o-Ps lifetime is one of the most useful methods for positron and positronium chemistry. This is because o-Ps lifetime contains information about electron density, which governs the basic properties of chemical bonding in molecules. It is also controlled by the physical structure of molecules. 

Existing books and articles on positron and positronium chemistry and annihilation... 

Billard, Ed. Fourth International Workshop on Positron and Positronium Chemistry, J. De Physique, Vol. 3, Coll. N 4, Suppl. JP, n 9, Les Ulis Cedex A, France Zone Indu. De Couttaoeuf, (1993). 

Zs. Kajcsos, B. Levay, K. Suvegh, Eds. Proceedings of the 5 h International Workshop on Positron and Positronium Chemistry, J. Radioanal. Nucl. Chem., Akademiai Kiado, Budapest Elsevier Science, A (1996). 

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