Answer:
The measurements are affected by the air mass
Step-by-step explanation:
The radioactive emission consists of alpha, beta and gamma rays.
The alpha particles are helium nuclei, with two positive charges and four um, so they are quickly stopped, by the layer of air around the emission zone, part of Radio.
Beta particles are electrons with a negative charge and the mass of the electron, they penetrate the air layer more and need denser materials to stop them
Gamma rays are waves of electromagnetic radiation, without electric charge or resting mass, which are very difficult to stop
With the above the sentence should be completed:
The measurements are affected by the air mass