Know Nuclear  Protecting Against Radiation Exposure  Time,
Distance and Shielding There are three general guidelines for
controlling exposure to ionizing radiation:  Time is an
important factor in limiting exposure to the public and to
radiological emergency responders. The amount of radiation
exposure increases and decreases with the time people spend near
the source of radiation. The maximum time to be spent in the
radiation environment is defined as the stay time. The stay time
can be calculated using the following equation:  Stay Time =
Exposure Limit/Dose Rate  Distance can be used to reduce
exposure. The farther away people are from a radiation source,
the less their exposure. Doubling the distance from a point
source of radiation decreases the exposure rate to 1/4 the
original exposure rate. Halving the distance, increases the
exposure by a factor of four.  How close to a source of
radiation can you be without getting a high exposure? It depends
on the energy of the radiation and the size (or activity)