In this laboratory session, tree experiments are proposed: the measurement of X‐ray energy spectra from radioactive sources with a high resolution cooled Si‐Li detector, with a room temperature PIN diode and the measurement of the response of a PIN diode to the intensity of X‐rays of radio‐diagnostic units. The spectra obtained with the Si‐Li detector help to understand the energy distribution of X‐rays and are used as a reference to compare the results obtained with the PIN diode. Measurements in medical X‐ray machines are proposed. Low cost, simple electronic instruments and systems are used as tools to make measurements in X‐ray units used in radio‐diagnostic. © 2003 American Institute of Physics