Refining the measurement of the attenuation coefficient of lead in modern physics laboratory activities

Contents related to the modern physics field involve the knowledge of the production and interaction of radiation with matter. The attenuation of the radiation evidences the macroscopic manifestation of this interaction. This study presents an apparatus intended for teaching practices to determine the lead mass attenuation coefficient for gamma-ray photons from a source of ¹³⁷Cs (photons with energy of approximately 662 keV). Traditionally, this determination is performed using lead plates of known thicknesses. However, this focus generally produces discrepant results related to the mass attenuation coefficient adopted values, with deviations around 15%. In the approach presented here, which is innovative, the plates were replaced by small spheres or powders of the analyzed material (lead). The results show that this substitution significantly reduced the deviations from the theoretical values. In the best experimental condition, the errors were between 2% and 4% for the spheres and the powder, respectively. Among the advantages of the proposed method are the possibility of continuous variations in the thickness and the geometry of the attenuating material, and the analysis of the influence of porous systems on the measurement of radiation attenuation.

Keywords
Modern Physics Laboratory; Gamma radiation; Mass attenuation coefficient; XCOM