A radioactive rock is placed near to the front of a Geiger-Müller (GM) tube. A radioactivity count-rate is first made in air. The count-rate is measured again with each of three different absorbers between the rock and the GM tube. A scientist has an idea that the rock emits three different types of radiation. Explain how the data in this table supports the scientist’s idea – 8022

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1. There is some evidence that alpha particles are being emitted because the count rate drops when paper is placed in front of the source. This makes sense because alpha particles can’t get through paper.

   There is stronger evidence for beta radiation because when a sheet of aluminium is put in the way, the count rate goes down a lot. That shows that beta particles were being stopped by the aluminium, which is typical because aluminium can block beta but not gamma.

   There might also be gamma radiation, but it depends on the count rate after using lead. If lead is used and the count rate still isn’t zero, then gamma rays are getting through, since lead blocks alpha and beta. But if the count rate drops to background level with lead, that means there’s probably no gamma radiation present.

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