Radiation
A good summary is in the PADS for ionizing radiation (On page 11 are the workplace exposure limits, PELs.).
Note the exposure of the whole body is the "effective dose" as we have been discussing. The exposure to special organs, such as the lens of the eye, is calculated based on the Annual Equivalent Dose and is more complicated.
While these limits are legal, the current philosophy of all the regulating and recommending bodies is that all radiation exposures be held to ALARA, as low as reasonably achievable.
There is exposure to naturally occurring radiation as well. The EPA recommends:
the public's annual exposure should not exceed 100 milli-REMs (mREM) if the
exposure is continual or frequent, and 500 mREM for infrequent exposures. Exposure
of an embryo/fetus should be held to less than 50 mREM per month.
Contrast those recommendations with natural background of 100 to 200 mREM, or
an X-ray technician that might be exposed to 10 mREM each month.
Workplace Monitoring
The most important item is to know what type of radiation you are monitoring
for, that is, its source.
The classic monitoring device is the Film Badge. These have some photographic
film inside a paper or plastic cartridge. The film is exposed by radiation.
The badge must be sent to a laboratory to be interpreted, and this delays results.
Film badges are the standard for low level exposures; they integrate the exposures
over the time the badge is worn. The badge is only good for gamma and x rays,
and some types of beta radiation. Thermoluminescence detectors have the same
advantages and disadvantages as film badges.
Pocket dosimeters can only measure Gamma, X-ray, “maybe” Beta, but
they give real time results.
Geiger-Mueller Counters use an ionization chamber that measures the current
from atoms that have been ionized by radioactivity. But they only measure, again,
beta, gamma, and X-ray. However, they are very sensitive and give immediate
results.
Scintillation types of meters, at least some of them, can measure alpha particles
as well. Again they give real time results.
Here is a web site with lots of meters, click on some of the general types. Ludlums. You might see some of the detectors. They also show a meter for measuring neutrons. PE Major
would be right at home.
I'll finish this long submodule with a few words about radon. Radon is an occupational
hazard of uranium miners and an environmental hazard for many of us. The uranium
isotope, U-238, occurs naturally in rocks and slowly decays to radon, an inert
gas with half-life of 4 days. The gas can percolate up through the rocks and
enter homes via the basement. If the radon itself decays while in transit, it
forms a series of daughter products. These isotopes are ions with half-lives
of minutes. The electrically charged daughters cling to dust and can be inhaled.
On their next decay, they will emit alpha particles which may be in close proximity
to lung tissue. Lung cancer is an occupational hazard of uranium workers. (Although
it is greatly exacerbated if the miners smoke cigarettes.)