Gamma Rays Flux Attenuation Height Dependence

When gamma rays propagate through medium, different types of interactions might occur (photoelectric, Compton scattering and pair production). These interactions with the medium leads to attenuation of the flux in such a way that the further the ray propagate through the medium, there are more interactions and the attenuation is greater. As we know different material has a different attenuation coefficient for different energies (of the photons).

Air monitoring of ground surface contamination at 50 - 1,000 m high above the ground has a few effects: distance, attenuation of air and humidity, buildup, background of terrestrial radiation and background of cosmic radiation. Detection of radioactive materials (emitting gamma rays) on the ground (or few meters above the ground) in a wide space might be done easily using aerial detectors (on a helicopter, a drone and such). By using those types of the detectors there is a gap of few hundred meters between them and the source. In this gap the flux attenuation of the rays is more complicated because in these heights we need to take in consideration the change in the dry air concentration (that varies as we travel farther from the ground) and in the humidity. We also need to take in consideration the change in the cosmic radiation that will affect the detector`s measurements significantly and will continue to grow as we go higher. Understanding the effects of the height on the gamma ray`s attenuation has an integral part in the process of finding out important details about the contamination (taking into consideration also the different efficiencies of the detector).

This work describes a way to calculate the change in the gamma ray`s flux for several materials of interest (i.e.Cs¹³⁷, I¹³¹ and a general mixture of them) for different heights (as we go farther from ground level), taking into consideration all the parameters mentioned above.