IONIZATION CROSS SECTIONS FOR MULTIPLY IONIZED TARGET ATOMS AND THE X-RAY PRODUCTION EXCITED BY COBALT IONS

The K, L, and M X-ray yield cross sections were measured for elements from Ti to Bi excited by accelerated beams of 94.4 MeV 59Co12+ ions. The results were compared with the predictions of the ECPSSR and PWBA theories, calculated using the ISICS11 program. The obtained data show that the overall decrease in the K-shell X-ray yield cross section with increasing atomic number of the target is accompanied by an increase over the range from Z2 = 22 to Z2 ≈ 41, with a maximum at Z2 ≈ 29. This phenomenon can be explained by the fact that near-symmetric interactions allow electrons to move between the orbitals of colliding atoms through the resulting molecular orbitals. Consequently, the X-ray production cross section for a given chemical element can be selectively maximized by selecting the irradiation mode – the energy and type of the incident ion – during PIXE analysis. Based on the shifts and broadening of X-ray lines in the obtained spectra, fluorescence yields and K-shell ionization cross sections were calculated for elements from titanium to molybdenum, modified for multiple ionization. The results show that the differences between fluorescence yields accounting for multiple ionization and single-vacancy fluorescence yields do not exceed 35%. Consequently, the observed deviations of experimental data from theoretical ones cannot be explained solely by multiple ionization without invoking effects associated with interorbital electron transitions.

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