M-shell x-ray production by 0.8--4.0-MeV 4He+ ions in ten elements from hafnium to thorium

M-shell x-ray production cross sections are reported for 72Hf, 73Ta, 74W, 75Re, 76Os, 77Ir, 78Pt, 79Au, 83Bi, and 90Th bombarded by 4He ions of energy 0.8--4.0 MeV. The measured cross sections are compared with the predictions of the semiclassical and first-order Born approximations and the calculations of the perturbed-stationary-state (PSS) theory that accounts for energy-loss (E), Coulomb deflection (C), and relativistic (R) effects (ECPSSR). The ECPSSR theory gives the best overall description of the measured data, although systematical discrepancies are found in the low-velocity region. Apart from deficiency of the available M-shell Coster-Kronig factors and fluorescence yields near or above Z2=74, where strong M4-M5N6,7 Coster-Kronig transitions become energetically forbidden, the increasing underestimation of the data by the ECPSSR theory with decreasing projectile velocities is genuine. In fact, we have found previously [Pajek et al., Phys. Rev. A 42, 261 (1990)] the same discrepancy for identical target elements bombarded by protons at comparably low velocities