Summary
By using the previously reported approach, which combines in a simple way the polarized orbital method and the JWKB approximation, phase shifts, differential elastic and momentum-transfer cross-sections are calculated for positron-alkali stom collisions for the energy rangeE=0.54 to 6.66 eV. The differential cross-sections exhibit a deep minimum near ϕ=90° at low energies, while the momentum-transfer cross-sections are fitted well by the lawC/E, allowing the analytical determination of equilibrium positron distribution functions in a gas of alkali atoms in the presence of an electric field. Results on positron energy loss rates are also reported. Whenever possible, the situation encountered in the positron-alkali atom gas interaction is compared to the corresponding situation of the positron-noble-atom gas. The reported nesults, while being obtained as a rule by adopting very simple procedures, are hoped to be useful in stimulating more accurate and extensive work in this new and perspective field.
Riassunto
Si usa l'approccio presentato in precedenza e che combina in modo semplice il metodo degli orbitali polarizzati e l'approssimazione JWKB, per calcolare spostamenti di fase, sezioni d'urto differenziali e di trasferimento di impulso nell'intervallo di energiaE=(0.54÷6.66) eV. Le sezioni d'urto differenziali mostrano un minimo profondo vicino ϕ=90° per basse energie, mentre le sezioni d'urto di trasferimento di impulso sono approssimate bene analiticamente dalla leggeC/E. Questa circostanza consente la determinazione analitica di funzioni di distribuzioni positoniche all'equilibrio in un gas di atomi alcalini in presenza di un campo elettrico. Si riportano anche risultati sul tasso di perdita d'energia da parte dei positoni. Dovunque possibile, si confronta la situazione fisica tipica dell'interazione positone-atomo alcalino con quella corrispondente positone-atomo nobile. I risultati riportati dovrebbero essere utili per stimolare un lavoro più ampio e più accurato in questo nuovo e promettente settore.
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Ferrante, G., Cascio, L.L. & Zarcone, M. Cross-sections and velocity distribution functions for elastically scattered positrons by alkali atoms. Nuov Cim B 44, 99–122 (1978). https://doi.org/10.1007/BF02730334
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DOI: https://doi.org/10.1007/BF02730334