Health Risks of Ionizing Radiation: - Clark University

72 Radiation Workers
• 50 rem (0.5 Sv) per year for the shallow dose
equivalent (SDE), which is the external dose to
the skin or to any extremity.
• For workers under 18, the annual occupational
dose limits are 10 percent of the dose limits for
adult workers.
• For protection of the embryo/fetus of a declared
pregnant woman, the dose limit is 0.5 rem (5
mSv) during the entire pregnancy 2 .
In order to remain in compliance with
occupational exposure regulations the owners of
nuclear facilities must monitor the exposure of their
employees. The first external monitoring devices were
pocket ionization chambers and pocket dosimeters;
these were basically pen-sized tubes containing a
wire with an electrical charge that decreased upon
exposure to radiation (Figure 6-2a). These devices
were later replaced by film dosimeters, which were
less expensive, more reliable, and could be attached
to a worker’s security badge. The film on the badges
reacted to radiation by darkening and could later
be analyzed to estimate exposure (Figure 6-2b).
Some facilities switched to thermoluminescent
dosimeters in the early 1970s. These dosimeters
contain light-emitting crystal phosphors that can be
read by a computer after they have been exposed to
radioactive energy. In 1994 researchers found that
Figure 6-2(a). The first external monitoring devices were
pocket ionization chambers and pocket dosimeters
(basically tubes the size of pens containing a wire with
an electrical charge that decreased upon exposure to
radiation) (http://www.ieer.org/sdafiles/vol_8/8-4/devices.
html).
2 www.state.ma.us/dph/rcp/faq13.htm
3 tis.eh.doe.gov/ohre/new/findingaids/epidemiologic/ rockyplant/employ/intro.html
many film badges worn from 1953 to 1967 had been
consistently misinterpreted, causing exposures to be
underestimated 3 . In the early stages of monitoring
workers for radiation exposure nasal swipes were
used for internal alpha radiation monitoring; this
method was later found to be unreliable. Urine
and blood sampling was added, and when used in
conjunction with the nose swipes, provided better
estimates of internal exposure 3 .
Assessing risks. There are many factors to
consider when determining the health risk involved
with occupational exposure. Researchers can compare
disease incidence among workers with national or
local populations, for example using standardized
mortality ratios (SMRs), but this task is complicated
by the fact that workers usually exhibit lower
disease rates and lower death rates than the general
population. This is a predictable situation because
the ill, weak and disabled are usually excluded from
employment; among epidemiologists this pattern is
referred to as the healthy worker effect. This can be
dealt with by comparing disease rates in exposed
workers to disease rates in similar groups of workers
who are not exposed to radiation. In section 5, for
example, we saw how military personnel who were
exposed to fallout from nuclear weapons testing
were compared to military personnel who were not
present at the tests. This is often not done, however.
Figure 6-2(b). Pocket dosimeters were replaced by film
badges. A worker here is pictured checking film badges in
1974 (imglib.lbl.gov/...index/97702936html.