The X-ray penetration intensity during the diffusion process of NH4Br into H2O was measured by a CdTe line sensor as a function of time and it was converted to the NH4Br composition using a calibration line. The diffusion coefficient of (NHBr)-Br-4 into H2O was estimated to be 2.2 x 10(-5) cm(2)/s by comparing the calculated results. The method was applied to the growth of InGaSb from the In-Ga-Sb solution. The indium composition profiles in the solution were measured and growth of InGaSb from the In-Ga-Sb solution was observed from the change of X-ray intensity. The growth region of InGaSb crystal was confirmed by the electron probe microanalysis. It was demonstrated that the X-ray penetration method was a powerful method to measure the composition profiles in the solution. (C) 2007 Elsevier B.V. All rights reserved.