Hi, I know that it not a forum of physicis, but anyways I would like to try to ask you whats happening in the following.

First of all there is a source of radiation, specifically "Radio" which emits a fixed steady energy. But I have put on its way several laminas of poliethilene. 1 piece of 0,2cm, 2 pieces(0,4), 3 pieces(0,6cm) Ive got different values( something normal) in the lab. But I do not know why at the moment of calculating the linear attenuation coefficient is different in each case. Should it not be the same in those three? In fact it is the same material, the only thing is different, it is the distanced travelled. So I do not know the reason of these different results.

This question is just because the exercise asks me about the linear attenuation coefficient of the material. But I have come across with this problem... Thanks