The personal dose equivalent at
10 mm depth, Hp(10), is used to provide an estimate of effective dose for
comparison with the appropriate dose limits. As Hp (0.07) is used to estimate
the equivalent dose to skin, it should be used for extremity monitoring, where
the skin dose (500 mSv) is the limiting quantity. It is also possible to use
the TLD cards to assess beta ray doses provided that the beta ray energy is
greater than 70 keV. Beta rays below this energy will not reach the TLD card.
In nuclear fuel cycle facilities,
personnel are exposed to various types of radionuclides of different energies.
Radiation environment is different in different facilities. Skin dose for the workers
can be significant. Estimate of the skin dose is not easy. It depends on energy
spectrum and the dosimeter used. Often, one has to calibrate the dosimety
system for a particular facility.
The absorbed doses by the TLD
below the open window of the cassette used to hold the card, and the TLD under
the plastic filter are used to estimate the beta component of the exposure. The
estimates needs to be multiplied by the tissue weighting factor for the skin
(0.01) to get the contribution of the skin dose to the whole body dose. This needs
to done and entered in the personnel dose records, particularly so for the
workers in: nuclear fuel production and fabrication facilities; in fuel
reprocessing plants; workers near spent fuel storage bays and operators of radiopharmaceutical
production facilities.
