K-shell ionization of Dy atoms produced in 158Gd(α xn) reactions

The K shell ionization cross-sections, σsup(K)sub(Z+2), are determined for the product atoms of 158Gd(α, xn) sup(162-x)Dy reactions in the 47-130 MeV bombarding energy range. The determination is based on the measured intensity ratios of the characteristic K X-rays of Dy and Gd elements. Analysis of the simultaneously measured discrete in-beam γ-ray spectra of sup(162-x)Dy isotopes yields lower limits for the Z + 2 ionization cross sections, σsup(Kder)sub(Z+2), derived with the use of known K shell internal conversion coefficients. The measured and the derived values are found to be identical within the experimental errors. Mean numbers of K shell ionizations per nuclear reaction are determined for the combined effect of all the (α, xn) reaction channels at each bombarding energy as well as for every channel separately. Experimental values of nuclear reaction cross-sections, σ(α, xn), are used. These were obtained previously with normalization to the same K-shell ionization cross-sections for the Gd target atoms as used presently to obtain σsup(K)sub(Z+2). The resulting σsup(K)sub(Z+2)/σ(α, xn) ratios are thus free from the normalization errors. The values of these ratios are found to be practically independent of the alpha bombarding energy for each (α, xn) reaction channel separately. On the other hand, they are found to vary strongly from one final nucleus to another. In the case of deformed final nuclei this variation is manifested as a large even-odd staggering, with the values for odd-A nucleides larger by a factor of 3-4 than those for the even A ones. (author)