K X-ray spectra from zirconium, niobium, molybdenum and paladium targets bo
mbarded with 25 MeV/amu helium and 22.5 MeV/amu oxygen ions were measured u
sing a high resolution transmission bent crystal spectrometer. Ratios of th
e double to single K-shell ionization cross sections were obtained from yie
lds of the K hypersatellites and diagram lines. The results are compared to
the semiclassical approximation predictions within the independent-particl
e model.