The K shell X-ray intensity ratios K-alpha 2/K-alpha 1, K-beta 1,K-3/K-alpha 1 and K-beta 2/K-alpha 1 for 21 elements with 65 <= Z <= 92 have been measured using an incident photon energy of 123.6 keV. The X-rays have been measured with a Si(Li) semiconductor detector. K-beta and K-alpha X-rays have been analyzed into the components K-beta 1,K-3 and K-beta 2 and K-alpha 1 and K-alpha 2, respectively, using a computer program. The experimental results were compared with the theoretical values of Scofield and available experimental results. All X-ray intensity ratios values have been plotted versus atomic number. (C) 2008 Elsevier Ltd. All rights reserved.