A student measures the radiation level coming from a radioactive substance. The detector is positioned very close to the substance. Different absorbers are then placed between the radioactive substance and the detector. The student’s findings are given below, after correction for background radiation. Absorber and counter reading (counts per minute): - no absorber: $95$ - thin paper: $52$ - a few mm of aluminium: $52$ - several cm of lead: $12$ Which types of radiation are being emitted by the substance?
- A$\alpha$-particles and $\beta$-particles only
- B$\alpha$-particles and $\gamma$-rays only
- C$\beta$-particles and $\gamma$-rays only
- D$\alpha$-particles, $\beta$-particles and $\gamma$-rays