Dosimeters
Devices for monitoring radiation
exposure to personnel are called dosimeters. Radiation workers who are issued
single badges for monitoring whole-body dose should wear them in the region of
the collar with the label facing out. When a lead apron is worn, the dosimeter should
be outside of the lead apron. Technologists who work with fluoroscopy may wear
two badges, one on collar outside the lead apron and one at the waist that is
under the apron. The two dosimeters should be distinguished by color or icons
indicating their specific locations. Personnel who are issued dosimeters should
wear them at all times when working in radiation areas, and should keep them in
a safe place, away from radiation and heat, when off duty. In addition to
wholebody badges, ring dosimeters may be worn by nuclear medicine technologists
and others whose work results in more exposure to the hands than to the body.
Film Badges
Film badges were once the principal
type of dosimeter. They are still in use today, but are much less common. They
consist of one or two pieces of dental film, paper-wrapped and enclosed in a
badgelike holder. Several filters are incorporated in the badge so that if the
unfiltered exposure exceeds the capacity of the film, additional exposure can
be measured in the filtered area. The disadvantage of this type of personal monitor
is that the dental film is subject to fog when exposed to heat or fumes, and this
exposure could result in a false reading. The film is also ruined if it is laundered!
After a period of use, the film is returned to a laboratory that processes it
and measures the OD of the film. The exposure is calculated and reported based
on this measurement. Many radiographers still refer to their dosimeters as
"film badges," but today they are more likely to be TLDs or OSLs.
Thermoluminescent Dosimeter (TLD)
TLD stands for thermoluminescent
dosimeter. The roots of this term mean "dose-measuring device that gives
off light when heated." The TLD is a type of personal monitor commonly
used by radiographer 36). It consists of a plastic badge or ring containing one
or more lithium fluoride crystals. These crystals (and several others with
similar characteristics) absorb x-ray energy and, when heated, give off the
energy again in the form of light. The TLD is more durable than the film badge
insert and responds only to ionizing radiation exposure. At the end of the
measurement period, the badge is sent to a laboratory where the crystals are
placed in a special tray and inserted into the TLD analyzer. This instrument
heats the crystals to the required temperature, measures the light emitted, and
transmits the data to a computer.
Optical Stimulated Luminescence (OSL)
OSL stands for optically stimulated
luminescence and refers to the most recently developed monitoring dosimeter.
Aluminum oxide is the radiation detector in this device. The dosimeter is
processed using a laser rather than heat as for TLDs. OSLs have several
advantages over TLDs. They can measure very small doses more precisely and can be
reanalyzed to confirm results. They are accurate over a wide dose range and
have excellent long-term stability.
Radiation Monitor Badge Service Laboratories
Radiation monitor badge service
laboratories provide dosimeters, processing services, and reports, and keep
permanent records of the radiation exposure of each person monitored. Service
may be arranged on a weekly, monthly, bimonthly, or quarterly basis. Personnel who
receive relatively high doses of occupational exposure change their badges most
frequently. With the exception of OSL badges, dosimeters cannot accurately
measure total exposures of less than 5 mrem (0.05 mSv). For this reason,
personnel who receive very small amounts of exposure will get more accurate
measurements with less frequent badge changes. Personnel involved in diagnostic
radiography who are always or nearly always in a control booth during exposures
are usually best monitored with quarterly service. Monthly service is a better
choice for those who work in fluoroscopy and those who perform bedside
radiography.
Service companies provide an extra
dosimeter in every batch that is marked "CONTROL." The purpose of
this dosimeter is to measure any radiation exposure to the entire batch while in
transit. Any amount of exposure measured from the control badge will be
subtracted from the amounts measured from the other badges in the batch. The
control badge should be kept in a safe place, away from any possibility of
x-ray exposure. It should never be used to measure occupational dose or for any
other purpose.
Radiation badge service companies will
want to know the name, birth date, and Social Security number of all persons to
be monitored so that all records can be accurately identified. If there has been
a history of previous occupational radiation exposure and the dose is known,
this information should also be provided so that the record will be complete
and accurate. Exposure reports are sent to the subscriber for each batch, and
an annual summary of personal exposure is also provided. Radiation workers
should be advised of the radiation exposure reported from their badges and should
be provided with copies of the annual reports for their own records. Employees
exposed to ionizing radiation should not leave their employment without a
complete record of their radiation exposure history. Employers are required to
provide this information.
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