Troxler 3411-B, Manual Of Operation And Instruction

Page: 80 / 109

Appendix B-4
Radiation Terminology
Various standards for the measurement of radiation exist, but
only two concerns the Troxler 3400-B Series gauge user. These
units are the
curie
, which expresses activity of the source, and
the
rem
(roentgen equivalent man). The curie, defined as the
quantity of radioactive material giving 3.7 x 10
10
disintegrations
per second, is equal to the number of disintegrations/second of
one gram of radium-226. Note that the source used in the 3400
series gauges is small, with quantities expressed in millicurie
(mCi).
The
rad
or "radiation absorbed dose," is the unit of absorbed
dose that is equal to 0.01 Joules/kg in any medium. In order to
take into consideration the effect of various types of radiation
on biological tissue, the rem, or more appropriate for Troxler
users—the millirem—is used to measure radiation dosage. The
unit rem is derived from scaling the radiation absorbed dose
(rad) by a quality factor (QF). One rad is equal to the exposure
of one rem of photon radiation. For example, the average
neutron energy of an americium-241:beryllium source is about
4.5 MeV. The quality factor (QF) for this radiation is about 10.
The absorbed dose of 1 rad of neutron radiation produces a
dose equivalent of (absorbed dose x QF) 10 rem.
Occupational exposure limits are set by government agencies.
The current limit in the United States and many other countries
is 5,000 millirem per year. Under average conditions, a full time
employee working with a 3400 series gauge will receive less
than 200 millirem per year.
Anyone working with or near radioactive materials is subject to
the limits on occupational exposure mentioned earlier and must
complete a radiation safety training course to be designated an
authorized user. As an authorized user, an individual so
designated must work in a "controlled" environment to the
extent that their exposure to radiation must be monitored.
Several means of personnel monitoring or
dosimetry
exist; the
most common methods are film badges and TLD badges.