Atomic Physics with Positrons by Wilhelm Raith (auth.), J. W. Humberston, E. A. G. Armour

April 3, 2017 | Physics | By admin | 0 Comments

By Wilhelm Raith (auth.), J. W. Humberston, E. A. G. Armour (eds.)

The NATO complex examine Workshop on Atomic Physics with Positrons, which was once held at collage collage London in the course of 15-18 July 1987, was once the fourth assembly in a chain dedicated to the final topic of positron colli­ sions in gases. prior conferences were held at York college, Toronto (1981); Royal Holloway collage, Egham (1983) and Wayne nation Uni­ versity, Detroit (1985). fresh very major advancements in positron beam currents, as a result improvement of extra effective moderators and using extra extreme positron assets, are making attainable an more and more subtle variety of experiments in atomic collision physics. while many years in the past merely overall scattering pass sections can be made up our minds, measurements can now be made up of numerous partial and differential pass sections. extreme positron beams also are getting used to provide positronium beams and already, as said the following, initial investigations were made from collisions of positronium with numerous goal platforms. those experimental advancements have prompted, and been prompted by means of, regular, if slightly much less spectacu1ar,progress in linked theoretical stories. either features of the sphere are good represented in those continue­ ings.

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The target can be moved along the axis up to the defining aperture and Figure 7 also contains a plot of the 511 keV rates recorded at various distances along the cell. ' Helium gas has been investigated between threshold and 125 eV. After normalizing our relative value to that of the Bielefeld group (14) at 40 eV, good agreement was obtained over most of the energy range. At present the statistical error on our data are at the ± 10% level. Further investigations will be carried out to ascertain whether this method can yield accurate relative/absolute values for aps.

I ....... ""':........ ,-----,:-==--- ",,"'-: . 'I' ,. _'-. - ... ~ .. '·1' . ,'-..... ", ",~~I-- " Fig. 9. 24 dOp /dn system proposed by E. Horsdaal-Pedersen (21). The fast o-P~ produced at various points along the scattering cell may pass through the 1 mm annular aperture to the position sensitive detector. most useful at the higher impact energies since its detection efficiency can easily be shown to be peaked around 40-60 0 (the Thomas angle for e+ is 45 0 ) with an ideal resolution of = 30 (22).

As shown in Figure 10, in the low energy region Tt~ for e+ and e- are high, but 1/4 or 1/3 of the theoretical values of Jain • This large discrepancy with the theoretical data is not understood. In the energy range below 2 eV and above 200 eV, the TCS values for e+ and e- colliding with H20 coincide with each other, as shown in Figure 11, and those with NH3 show the same tendency. These results show that the Born approximation is a fairly good approximation for these regions. One of the characteristics of scattering by polar molecules is that the cross section for Ps formation is very low.

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