A satellite peak resolved on the high-energy side of K, and K, x-ray groups excited by 2g50MeV protons in tantalum is studied, and its production mechanism is determined to be the result of de-excitation by internal conversion of the product nuclei from (p, xn) reactions. Satellite peaks associated with the production of K, and K, x-rays in proton-induced fluorescence spectra have currently become the subject of considerable interest and research effort. Such peaks have been observed in a recent experiment at this labora- tory designed to measure the total K x-ray production cross sections for heavy ele- ments bombarded with 2&50 MeV protons. We have now attempted to determine the production mechanism for a particular satellite through measurement of the energy separation from normal K, peaks, AE,, and the energy dependence of the cross section. A recent paper (Dyson 1975) comments that a satellite can be caused by the de-excitation of an atom with a doubly ionized K shell. The first electron making a transition from the L shell can experience a larger potential difference than normal, namely EKz + AEq, due to the reduced screening caused by the absence of both K-shell electrons. This effect has recently been reported (Richard et a1 1972). Wolfli et a1 (1975) have demonstrated the presence of a further phenomenon, namely double ionization resulting in the simultaneous transition of two electrons from the L to the K shell producing a single photon of energy 2EK + AEs, or alterna- tively EK, + EKo + AEs. Again the factor AEs is caused by the reduced screening seen by the L-shell electrons in the absence of two rather than one K-shell electron. Neglecting fine structure splitting, AEs for the K, transition is given by