Here’s the rules. When handling IR (ionising radiation)
keep exposure short
get as far away as you can
get behind something dense
If exposed to ionising radiation, macromolecules which rely on precise conformations are damaged, change shape and don’t work. DNA and other nucleic acids can’t repair themselves and replicate nonsense proteins. Irradiating water produces highly reactive free radicals which have biological implications since water is a universal solvent.
Absorbed dose D is defined as the energy absorbed per unit mass or tissue or absorber, so D = E/m of irradiated material in J/kg
where D is 1J/kg = 1 GRAY (Gy) or the old unit, the rad, 100 rad = 1Gy
Damage H produced is in “dose equivalents” since the ionising damage is dependent on radiation type. Q is a quality factor , a dimensionless integer, 1 for betas and gammas, 20 for alpha particles.
A dose of 0.01mSv is received from
- an average year of TV watching
- an airline flight from New York to San Francisco
- a year living next door to a normally operating nuclear power plant
Maximum permissible dose is a dose level applied to workers in the radiation industries, including hospitals, and is about 50mSv per year from a variety of background sources, chest X-rays and so on. Workers are regularly monitored in hazardous environments.
The loss in life expectancy from a 0.01mSv dose is about 1.2 minutes, equivalent to crossing the street three times or three puffs on a cigarette. Eating a banana contributes 1 uSv (microsievert)
A dose of 5Sv is huge – causing massive tissue breakdown, consequent internal bleeding, and death within about six weeks. Some Hiroshima victims may have received as much as 100Sv. It was said that if you survived the first three weeks, you might just pull through.
Look at Q1 and 2 on P 714
Sometimes, an alternative unit, “exposure”, E, can be used. If you are sheltering behind something dense, your dose is less than if you were “exposed”. The unit for exposure is charge-dependent and is in C/kg. Put simply, we can calculate that D = 34E in J/kg ( one ion requires 34eV to be produced in air)
where f is a quality factor – a dimensionless integer dependent either on photon energy or the material receiving the dose, and sometimes both.