The first lesson of radiation worker training. Dose equals dose rate times time, so halving time halves dose. Dose rate from a point source falls with the square of distance, so doubling distance cuts it to a quarter. Dense or thick material absorbs radiation, so lead, steel, concrete and water reduce dose rate. Every work plan in a radiation area applies all three, from staging tools outside to using long-handled tools.
Time, distance, shielding, people: stage your tools outside, stand back off the pipe and work behind the blanket.
Distance is the cheapest of the three: one step back from a hot pipe often does more than an hour of shielding work.
Also heard as
- time distance shielding
Related terms
ALARA
As low as reasonably achievable: the principle of keeping doses as low as practical, not just below limits.
Shielding
Material placed between a radiation source and people to absorb radiation and reduce dose rate.
High radiation area
A posted area where a person could receive more than 1 mSv (100 mrem) in an hour at 30 cm from a source.
Hot spot
A small spot on piping or equipment with a much higher dose rate than its surroundings.