Consider the case of Sarah the molecular biologist. Sarah works with radioactive isotopes from behind a Perspex screen, 2 metres away from the source of radiation. She has a mass of 70 kg and an effective surface area of 0.7{m}^2 facing the radiation, and she spends approximately 10 hours a week, 45 weeks a year, working with radiation in this way. Calculate Sarah's annual radiation dose (in Sieverts) if her source of radiation is a sample of Cobalt-60 producing gamma radiation with an energy of 1.2 MeV = 1.92 \times 10^{-13} J per photon, at a rate of 40 mega-Becquerels (MBq). You may assume for this question that the Perspex screen does not block any of the radiation, however realistically this would serve to reduce the radiation exposure even more.

Note: 1 Becquerel (Bq) = 1 photon of radiation produced per second; 1 Sievert (Sv) = an absorbed dose of radiation energy of 1Jkg ^-1   .

If Sarah worked in exactly the same way but was 50 cm from the source instead of 2 m, would she exceed the maximum safe dosage?