The fundamental principle of radiation protection is to use the
principles of "TIME - DISTANCE - SHIELDING" to minimize your exposure
to radiation. These three elements are just as important to your personal
protection as gloves, lab coats, safety glasses, or fume hoods!
Time 
Your dose from a radiation source is directly proportional to
the amount of time you spend in the radiation field. Seems like common
sense, but not having the correct material, not having a well laid out work
plan, or just not being aware of how much time you are spending in the field can
all increase the amount of exposure you receive. Ways to decrease time
spent receiving radiation dose are: practice runs, mock-ups, planning, and
procedures.
Distance 
By increasing your distance from a radiation source, you
decrease the radiation dose you receive. This is not linear - dose rate
from a point radiation source decreases by the square of the distance. If
you double your distance from a source, the dose you receive from the source is
4 times less!
Shielding
It is important to use the proper shielding for the
radionuclide of concern. Sometimes the radiation from a nuclide may be
sufficiently shielded with air or thin rubber gloves. High energy gamma
emitters may require lead, steel, or concrete. Knowing what you are
dealing with is the first step to proper shielding.
Many things not normally thought of as shielding may be used to
shield you in a research laboratory - garbage cans, walls, and doors can be used
to reduce your exposure to radiation. How do you know if your shielding is
working? Most times by checking with a detection instrument which just
happens to be the next section.
One final note before we move on - all these concepts apply to
internal exposure as well. We shield ourselves from intakes with fume
hoods and respiratory protection when required. If there is an ingestion,
we can shield vital organs with "blocking agents". We prevent
the radioactive material from getting on us or in us, thus increasing distance.
And, if there ever is an ingestion of a radioactive material, there are also
methods to speed the material through the body to reduce the time of exposure.
