A practical instrument must tell us which type of radiation it is measuring,
as well as the intensity. An instrument may indicate that the radiation field
in a work location is
. This is not enough information to enable us
to assess the hazard.
For example, if the radiation being measured is gamma
radiation , we know we
would be exposed to an equivalent-dose rate of
to the whole body. If
the radiation is pure beta radiation , we would also be
exposed to , but would only get a
shallow dose , not a whole body dose
. Also the knowledge that
the radiation is due to beta rays would allow us to use
relatively light shielding
to eliminate the hazard almost entirely.
If the radiation is pure alpha radiation , there is no external hazard but we would have to take precautions to avoid ingesting the alpha emitting radioactivity .
If the radiation is composed of neutrons , the dose rate would have to be multiplied by the appropriate radiation weighting factor to give the equivalent-dose rate to the whole body.
Unfortunately, all radiation detectors respond to more than one type of radiation so instruments have to be designed such that only the effects of the kind of radiation we are trying to measure are recorded. Generally, in mixed radiation fields, a number of different instruments is required to measure the intensity of each radiation present.