Effect of the photon intensity selected at various positions under the photopeak on the mass attenuation coefficient of x-rays

The variation in the value of the mass attenuation coefficient of x‐rays in aluminium was studied by counting photons under various positions in the photopeak employing a proportional counter spectrometer system with a good geometrical set‐up. The effect of (small angle) scattering was also examined using three different sets of collimators of diameter 9, 6 and 3 mm and employing both a pure x‐ray source (55Fe) and a mixed radiation source (57Co). The μm values obtained at the FWHM position for each set of collimators agree closely with the theoretical values.