Thin aluminium foil is used for cooking. The diagram shows an arrangement used to regulate the thickness of aluminium foil produced in a factory. What is the most suitable radioactive source for the system?
- Abeta, half-life $1\text{ hour}$
- Bbeta, half-life $6\text{ years}$
- Cgamma, half-life $1\text{ hour}$
- Dgamma, half-life $6\text{ years}$