This previously unknown phenomenon taking place in radioisotopes and XRF sources was reported in Braz. J. Phy., 40, no 1, 38-46, 2010. Does the beta, gamma or X-ray knock out a core electron as happens in photoelectric effect or Compton effect?
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332010000100007