The diagram depicts an apparatus used to find out the nature of the emissions from a radioactive source. The absorbers may be lifted clear of, or lowered into, the path of the radiation travelling from the source to the detector. The apparatus has been evacuated. The table presents a set of results for one particular radioactive source. absorber in use: - none: 350 counts per second - thin paper: 350 counts per second - $1.0\,\text{mm}$ aluminium: 180 counts per second - $1.0\,\text{cm}$ lead: 23 counts per second Which types of radiation are emitted by the radioactive source?
- A$\alpha$-particles and $\beta$-particles
- B$\alpha$-particles only
- C$\beta$-particles and $\gamma$-rays
- D$\beta$-particles only