Question

A technician wears a 1 mm Pb equivalent lead apron. The HVL for the radiation with which she is working is 0.25 mm Pb. If the unshielded exposure level from the source with which she is working is 25 R/hr at 1 cm, what is the shielded dose equivalent rate, mrems/hr, at a distance of 1 m from the source?

Answer 1

The unsheilded exposure level is 25 R/hr at 1 cm, so the exposure at 100 cm will be, by inverse square law

E= (25 R/hr) /1002 = 2.5 mR/hr

Also the value of 1 HVL is 0.25 mm of Pb.

The lead apron thickness is 1 mm Pb equivalent, so we get

no. of HVL (n)= thickness/HVL= 1/0.25 = 4 HVL

Reduction factor will be, RF=2n =24 =16

the radiation at 1 meter with lead apron will be

E(at 1 meter, with lead apron) =(2.5 mR/hr)/16 = 0.156 mR/hr

we have, 1 R = 0.877 rem,

1 mR = 0.877 mrem

so , equivalent dose rate at 1m= 0.156 mR/hr = 0.156* 0.877= 0.1368 mrem/hr