Temperature effect on the two-gamma annihilation of positrons in bismuth

Faraci, G.; Quercia, I. F.; Spadoni, M.; Turrisi, E

doi:10.1007/bf02712366

Cited by 9 publications

References 2 publications

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On the diffractional mechanism of the temperature dependence of positron annihilation in single crystals

Dekhtyar

Mikhalenkov

1971

Physica Status Solidi (b)

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There are two hypotheses about the mechanism of the temperature dependence of positron annihilation in single crystals. This dependence was observed in a series of works (1, 2). The first hypothesis (3) suggests diffractional reflection of positrons from the corresponding crystal planes and their exit through a channel.The second one (4) suggests incomplete thermalization of positrons during their movement through channels that causes the appearance of annihilation photons at large angles which correspond to large momenta of annihilating pairs. The results given in (5) disagree with the latter hypothesis.To observe positrons which had diffracted from Zn single crystals with (0001) face we used a thin (50 pm) aluminium foil quasi-transparent for positrons (Fig. 1).The Zn crystal screened from the detectors was placed behind the foil and could be cooled with liquid nitrogen by the contact method (Fig. 1).If N(A1) is the number of positrons which, from the total quantity of incident positrons and N is the number of positrons which enter the Zn crystal, then, having in mind the thermal factor (e -2M) which takes into account the temperature dependence of positron diffraction from the Zn crystal (3), we find that , have annihilated in the aluminium foil in the presence of the Zn crystalwhere A is a temperature independent factor. Let TI and T be the corresponding temperatures of the Zn crystal when we measure the angular distributions of annihilation photons in the aluminium foil (Fig. 2) at room temperature. Then for the temperature dependence of positron annihilation in Zn we have 2

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