Positronium beams

The final method which is proving of value is the gas-cell technique, in which use is made of the natural peaking of the positronium formation cross section in the direction of the incident positrons (see Chapter 4 for further discussion of this feature) for the reaction described by equation (1.12). This method was pioneered independently by Brown (1985, 1986), and by Laricchia and Charlton and coworkers (Laricchia et al., 1986, 1987b, 1988), who have shown that a tunable positronium beam with narrow energy width can be produced by the capture reaction in gases. Further discussion of this technique, and some applications in atomic physics, can be found in section 7.6. 

Positronium beams may have a variety of applications. In surface physics the interest in positronium diffraction from crystals, as pointed out by Canter (1984), arises mainly from the fact that the relatively long de Broglie wavelength of positronium at intermediate energies enables the surface layers to be probed more deeply than is possible with traditional-atom diffraction. Weber et al. (1988) carried out a study of positronium reflection from a single crystal. Surko et al. (1986) proposed the injection of positronium atoms into a tokamak plasma to act as a... 

Fig. 7.23. Schematic illustration of the positronium-beam apparatus used for studies of positronium-atom(molecule) collisions (Garner, Ozen and Laricchia, 1998).

Fig. 7.24. Positronium-beam production efficiencies versus gas pressure at positronium kinetic energies of 30 eV, 60 eV, 90 eV and 120 eV for (o) helium, (A) argon and ( ) molecular hydrogen gases. The curves are polynomial fits to the data, which were performed by Garner, Laricchia and Ozen (1998).

Gamer, Laricchia and Ozen (1996) have published the most detailed study of the production of positronium beams by the gas collision method, and their results for molecular hydrogen, helium and argon gases at four... 

The photodetachment of Ps- was suggested by Mills (1981) as a potential source of a tunable-energy positronium beam. Once produced and accelerated electrostatically to the required energy, the Ps- would undergo photodetachment to form the desired beam according to... 

Brown, B.L. (1986). Creation of a monoenergetic positronium beam in a gas and measurement of positron survival fractions in a gas. In Positron(Electron)-Gas Scattering, eds. W.E. Kauppila, T.S. Stein and J.M. Wadehra (World Scientific) pp. 212-221. 

Garner, A.J., Ozen, A. and Laricchia, G. (1998). Positronium beam scattering from atoms and molecules. Nuc. Inst. Meth. B 143 155-161. 

Laricchia, G. (1995b). Positronium beams and surfaces. In Positron... 

For the exponential absorption law the characteristic thickness A within which the positronium beam intensity is reduced by a factor e has the following values for carbon, molybdenum and platinum... 

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