AcademyNuclear Physics
Academy
Biological Effects of Radiation
Level 1 - Physics topic page in Nuclear Physics.
Principle
Radiation risk depends on deposited energy per mass and the biological weighting of the radiation type.
Notation
\(D\)
absorbed dose
Gy
\(E\)
energy deposited
\(\mathrm{J}\)
\(m\)
absorbing mass
\(\mathrm{kg}\)
\(w_R\)
radiation weighting factor
1
\(H\)
equivalent dose
Sv
\(\dot D\)
absorbed dose rate
Gy s^{-1}
Method
Derivation 1: Absorbed dose
Dose measures energy deposited per kilogram of tissue or material.
Dose definition
\[D=\frac{E}{m}\]
Gray
\[1\,\mathrm{Gy}=1\,\mathrm{J\,kg^{-1}}\]
Derivation 2: Equivalent dose
Different radiations cause different biological damage for the same absorbed dose.
Equivalent dose
\[H=w_RD\]
Sievert
\[1\,\mathrm{Sv}=1\,\mathrm{J\,kg^{-1}}\quad\text{weighted}\]
Derivation 3: Dose rate
Risk also depends on exposure time and rate.
Dose rate
\[\dot D=\frac{D}{\Delta t}\]
Accumulated dose
\[D=\int \dot D\,dt\]
Rules
Absorbed dose
\[D=\frac{E}{m}\]
Equivalent dose
\[H=w_RD\]
Dose rate
\[\dot D=\frac{D}{\Delta t}\]
Examples
Question
\[0.020\,\mathrm J\]
is deposited in \[0.50\,\mathrm{kg}\]
Find \(D\).Answer
\[D=E/m=0.020/0.50=0.040\,\mathrm{Gy}\]
Checks
- Gray measures physical energy deposition; sievert includes biological weighting.
- Alpha radiation has high weighting but low penetration.
- External and internal exposure can have very different risks.
- Shielding choice depends on radiation type and energy.