Biological Effects of Ionizing Radiation
Radiation Dose
Radiation dose unit (rad) : 1 r = 0.01 J/kg
The biological effect depends on the type of radiation and body part:
RBE: Relative biological effectiveness
Roentgen Equivalent Man: rem = rad x RBE
Type of energy of radiation
X rays
Gamma rays
Beta rays > 30KeV
Beta rays < 30 KeV
Neutrons, slow
Neutrons, fast
Alpha Rays
RBE
1
1
1
1.7
2-5
10 (body) 30 (eyes)
10-20
Dose delivered in less than one day
Possible latent effects (cancer)
Total Average US Background Level Radiation: 382 mrem
Other Units
1 Gray (Gy) = 1 J/kg = 100 rad
1 sievert (Sv) = 100 rem
Sample Problem
Plutonium-239 decays by alpha emission with energy 6.02 MeV. If you inhale 1 milligram of
plutonium and it effects 1.00 kg of your lung, what would be your dose in rem if 50% of the
energy is absorbed? What biological effect would that have on your body? Assume the lowest
RBE for alpha particles.
energy
#decays x Energy/decay
dose =
=
mass effected
mass of lung