Positron beam in nuclear spectroscopy

The process of nucleus excitation and orientation in a positron radiationless annihilation (PRA) on the electron of the heavy atom shell is considered. Electron-positron factors are calculated to determine the excitation cross-section value in the PRA of the nuclear ΛL transitions (EL or ML). Coefficients fixing the orientation of the excitation nucleus angular momentum in relation to the positron momentum and hence the angular distribution of decay products of the excited nucleus are determined as well. Relativistic wave functions of the electron of the shell and of the positron are used in the calculations of the processes of ΛL multipolarities E0, E1, E2, M1,M2 in the energy range of the positron 0.55 MeV <= Esub(+) <= 6.55 MeV annihilating on K-shells of atoms with Z equal to 41, 49, 60, 70, 82, 92. In the case of lead (Z=82) L1-, L2-, L3-shells are considered as well. Results are given in a graphic form. The excitation of spontaneously fissioning isomers of 236U and 238U nuclei in different processes of the PRA on the atom K-shell is considered in the framework of different hypothesis of the spontaneously fissioning isomer state structure. The given cross section factors for uranium atom may be used in the Z region 90-96 as the factor dependence on Z is rather weak