A particular radioactivesource produces 150 mrads of 2.5 MeV gamma rays per hour

Question

A particular radioactivesource produces 150 mrads of 2.5 MeV gamma rays per hour at adistance of
1 m. a) HOw long could a person stand at this distance beforeaccumlating an intolerable dose of 1 rem b) Assuming the gamma radiation is emitted isotropically, atwhat distance would a person receive 15 mrads/hr from thissource? A particular radioactivesource produces 150 mrads of 2.5 MeV gamma rays per hour at adistance of
1 m. a) HOw long could a person stand at this distance beforeaccumlating an intolerable dose of 1 rem b) Assuming the gamma radiation is emitted isotropically, atwhat distance would a person receive 15 mrads/hr from thissource?

Explanation / Answer

r1 = 1m I1 = 150 mrad / hr I2 = 15 mrad/hr a) x-ray or -ray have 1.0 RBE ==> 1 rem = 100 x 10-3 rad / hr x 1 RBE x t(hr) ==> t = 10 hr b) We know that I = P / 4r2    ==> r2 / r1 = [I1 / I2]    ==> r2 = r1 *[I1 / I2]                = 1m * [ 150 mrad/hr / 15 mrad/hr]                = 3.162 m

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