Why should you think that more loss material between source and detector will increase the number of detections? This is a simple experiment. Test your assumption of increased detection. If you find that increasing interference increases detection, then you should explain how this happens.

Dear Joseph ,

thank you for reply , in fact we do this experiment and we found that the number of tracks in the detector placed at a 2cm distance is more than the number of tracks placed in touch with samples. but I need to see the opinion of other colleagues think about these two scenario and what is there explanation.

It will depend on the detection geometry and the energy of the alphas. If the SSNTD detector has the same surface as the sample, most likely putting it in touch with the sample will record more tracks than if put at a distance. If the SSNTD is considerably smaller than the sample, than putting it at a distance will increase the number of tracks due to the incident alpha particles from the adjacent surfaces, but there will be a balance between the increase due to the geometry and the loss due to absorption in air, which will depend on the energy of the particles.

Putting it in contact with the sample is the best idea, though, because it reduces the number of parameters you need to consider when you calculate the surface emission of the sample.

dear Radu , thank you very much for the interesting reply ,

your opinion is matching with my idea and results , and give me a good explain to the situation.

in fact when I see the difference in the number of tracks between the two detectors , I calibrate the difference in the surface area against the detector by divided the number of tracks on the surface area of the sample .