Lattice defects that contain hydrogen and helium in Fe and Fe-Cr have been studied by positron model calculations using Density Functional Theory (DFT) in its Local Density Approximation (LDA) implementation. It was found that the value of positron lifetime for perfect Fe lattice is 101.6 ps. and for mono vacancy is 176.6 ps. which a close to the experimental values. The calculated values of Positron Life-Time (PLT) for Fe-2.5% wt Cr is 104.7 ps., for Fe-5% wt Cr is 127.6 ps., for Fe-8% wt Cr is 128.9 ps. and for Fe-9% Cr is 128.2 ps. A correlation between the positron lifetime and H and He atom concentration has been established. The model calculations for PLT and Coincidence-Doppler-Broadening (CDB) for Fe-Cr containing vacations in the presence of different numbers of hydrogen and helium atoms will be presented.
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