A manufacturer needs to sterilise single-use plastic culture dishes. The dishes are sealed in plastic sleeves and packed inside closed cardboard cartons before treatment.
The plastic begins to deform at 80 ∘C80\ ^\circ\mathrm{C}80 ∘C. Steam sterilisation takes place at 121 ∘C121\ ^\circ\mathrm{C}121 ∘C.
The table shows the percentage of radiation from different sources that reaches the centre of a carton.
| type of radiation | radiation reaching the centre of the carton (%) |
|---|---|
| alpha | 0 |
| beta | 0 |
| gamma | 64 |
Explain which type of radiation should be used to sterilise the culture dishes. Use the information provided in your answer.