Dose Rate Calculations

No student is permitted to proceed to their experiment until they have verified that the dose rate they could receive is well within the limits laid down and have done the calculations enclosed with the notes on the experiment.

1. What is the dose rate 2m from a Co⁶⁰ source of strength 1mCi?
2. A cobalt 60 source has a dose rate of 40 mSv/hr at 1 m. What thickness of lead is required to reduce this dose to 2.5 猶v/hr?

Background Annual Exposures

In areas of normal background the average annual effective dose equivalent rom radiation of natural origin, from cosmic radiation, terrestrial gamma-radiation, internal radioactivity and inhaled radon is 2.0 mSv. In addition there is a population average dose of 0.25 mSv from medical procedures and 0.03 mSv from the sum of all other sources. The annual total is therefore 2.3 mSv.

Maximum Permitted Dose Rates

The International Commision on Radiological Protection has laid down a maximum permissible additional dose for ‘members of the public’ of 5 mSv in a year (students working in the Level 3 Nuclear Laboratory are classified as ‘members of the public’). The maximum dose-rate at the position of working is 2.5 micro-Sv hr^-1. This upper limit must be absolutely adhered to; and efforts should be made to keep well below the limit. A radiation monitoring instrument is available for measuring dose-rates at the seating positions of the students. No student is permitted to proceed to carry out their experiment until they have verified that the dose-rate they could receive is well within the limits laid down.