Students investigate a radioactive source. They place a detector close to a radioactive source and take 5 readings over 5 minutes. They then place a thin sheet of paper between the detector and the source, and again observe the counts over 5 minutes. Lastly they replace the paper sheet with an aluminium one and observe the counts over 5 minutes. Their results are shown below: What type(s) of radiation is being given off by the source.

Answer:

7) D

None of the radiation was stopped by paper, meaning no α radiation was present.

Some of the radiation was stopped by aluminium which means that ß radiation was present.

However, some radiation as still detect even after aluminium was placed which suggests that γ radiation was also present. 

So the answer is ß and γ which is option F.