Temperature dependence of the positron annihilation radiation spectra for aluminium by means of Doppler broadening measurement

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Abstract
Doppler broadened spectra of positron annihilation in an aluminium crystal were measured for 59 different temperatures from 298 to 897K. The instrumental response function was unfolded from observed annihilation spectra and intrinsic distributions were obtained. Two lineshape parameters S and W were defined for the central and the tail portions of the spectrum, respectively. It was shown that the fractional change of the W parameter is about one order of magnitude larger than that of the S parameter. The temperature dependence of S and W parameters in the prevacancy region does not correspond to that of the lattice volume. In addition, the S parameter shows strong temperature dependence in the high temperature region, in contrast to the W parameter which saturates in this region. Using the trapping model the vacancy formation enthalpy was obtained from the result. The value strongly depends on the fitting function for the lineshape parameters.

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