Given that the half-value layer of lead for a gamma photon of energy 0.5 MeV is 0.42 cm, which of the situations listed below would result in the LEAST exposure to radiation? Staying in the same room as the gamma source for

A: Choice B would result in 2 × the dose (due to doubling the time), multiplied by 4 × the dose (due to halving the distance) multiplied by ½ × the dose due to the extra half value layer = 4× the dose of choice A.

Choice C would result in 3 × the dose multiplied by 1/4 × multiplied by 2 × the dose = 1½ × the dose of choice A. Choice D would result in 8× the dose multiplied by 1× multiplied by ½ × the dose = 4 × the dose of choice A.