It depends on the source intensity and radioactive period of each one supposing that we are at the same distance from all sources

Hello.

The answer is not so simple as it may seems.

Firstly let's make an experimental setup clear.

• Lets suppose we are talking about a laboratory experiment (not some kind of outdoor measurement)
• radioactive sources are point-like and solid-state. (I.e. with no self absorption, no diffusing or flowing gasses or liquids, with no affinity to aerosols)
• it is an isotropic radioactive source without beam collimation
• radioactive sources are relatively close to each other (lets say 10 cm as you suggested)
• there is a standard atmospheric air between the radioactive sources, free of 222Rn and filtered for aerosols
• lab is perfectly shielded from surrounding environment and cosmic rays
• construction materials of experimental setup are free of radioactive isotopes

Then the measured activity of low radiation samples may strongly depend on where exactly is "somewhere in between".

First of all, isotropic flux of particles of photons (in vacuum) decreases as square of distance from source.

Flux of particles at particular point in space filled by some medium (air) depends on ability of particles to penetrate it. For example alpha particles are so highly ionizing form of particle radiation that they can be completely stopped even by a few centimeters of air (depending of alphaparticle energy).

Therefore, it is extremely important to know the details about the experiment to design the setup properly.

Bye, JS

1. Calculate the doserate from each source separately, as for a single source

2. Add the two doserates.