Expert: James J. Kovalcin - 8/28/2005

Question
A radioactive source can be used to check on the quantity of cereal in boxes. This is done by placing the radioactive source on one side of the conveyor belt which carries the boxes and a detector on the other side.

How can the half life of source affect the choice of radioactive source used? Is it true to say a lower half life would not give a strong enough radiation to render cereal harmful for consumption?

Thank You.

Answer
The half life of the radiation source is only relevant with regard to how much time passes before it will need to be replaced and to how much of the radioactive sample is required to do the job.
A more relevant factor will be the "half thickness", the amount of matter needed to reduce the radiation intensity by one half by absorbing the radiation energy.
The half life of the radiation source has nothing to do with the safety of the irradiated food. The effect on the food will be determined by the energy of the individual emitted radiation. Food irridation works because the emitted particles have sufficient energy to ionize [strip off electrons] the food sample. This breaks chemical bonds which is turn can kill harmful bacteria etc. Many foods are already irradiated on a common basis. [Strawberries, potatoes, spices and some meats]
Contrary to common belief, irradiation does NOT make the food radioactive. It can however affect the texture and taste of the food if the radiation level is high. Some people are concerned that irradiation can inadvertently produce unwanted chemical changes in the food. It is worth noting that similar effects are produced by cooking foods using high heat, particularly that produced by a charcoal grill.