The invention relates to the field of materials analysis by ionising radiation, in particular x-radiation or gamma radiation. The invention proposes a method for determining physical properties of a test sample (14) using a spectrometric detector (20) with at least three channels, consisting of: performing measurements in each of the channels on the test sample, calculating variables, each formedfrom a combination of measurements of different channels, applying a weighting and bias matrix to the variables, enabling the investigated physical properties of the test sample to be determined.