**Practice Problem 10**

Calculate the rems** **of radiation absorbed by the average
person from the

**Solution**

We can calculate the number of b-particles emitted per
second from the activity of the ^{14}C isotope:

To calculate the effect of this radiation over a year, we have to calculate the number
of ^{14}C nuclei that decay during this time:

We can now calculate the amount of energy absorbed per year from the number of atoms that disintegrate, the energy per disintegration, and the fraction of this energy absorbed by the body:

Before we can go any further, we have to convert this energy from units of million electron volts per year to joules per year:

Averaged over a 70-kg body weight, this amounts to about 1 x 10^{-5} J per
kilogram of body weight per year. If 1 rad is equal to 0.01 J/kg, the radiation
absorbed dose from ^{14}C decay is 0.001 rad per year. Using an RBE for b decay of 1, this corresponds to 0.001 rems, or 1 millirem per year.