Geoscience Reference
In-Depth Information
Half-life is defined as the time it takes for a material to lose 50% of its radioactivity. The follow-
ing equation can be used to determine half-life.
A = A i (0.5) t / T
(15.28)
where
A = Activity at time t .
A i = Initial activity.
t = Time.
T = Half-life.
15.9.8 r adiation d ose
In the United States, radiation absorbed dose , dose equivalent , and exposure are often measured
and stated in the traditional units called rad, rem , or roentgen . For practical purposes with gamma
and x-rays, these units of measurement for exposure or dose are considered equal. This exposure
can be from an external source irradiating the whole body, an extremity, or other organ or tissue
resulting in an external radiation dose . Alternatively, internally deposited radioactive material may
cause an internal radiation dose to the whole body or to an organ or tissue.
A prefix is often used for smaller measured fractional quantities; for example, milli- (m) means
1/1000 and 1 rad = 1000 mrad. Micro- (µ) means 1/1,000,000, so 1,000,000 µrad = 1 rad, or 10 µR
= 0.000010 R.
The SI system for radiation measurement is the official system of measurement and uses the
gray (Gy) and sievert (Sv) for absorbed dose and equivalent dose, respectively. Conversions are as
follows:
1 Gy = 100 rad
1 mGy = 100 mrad
1 Sv = 100 rem
1 mSv = 100 mrem
Radioactive transformation events (radiation counting systems) can be measured in units of disin-
tegrations per minute (dpm) and, because instruments are not 100% efficient, counts per minute
(cpm). Background radiation levels are typically less than 10 µR per hour, but due to differences in
detector size and efficiency, the cpm reading on fixed monitors and various handheld survey meters
will vary considerably.
REFERENCES AND RECOMMENDED READING
ACGIH. (2010). Industrial Ventilation: A Manual of Recommended Practice , 27th ed. American Conference of
Governmental Industrial Hygienists, Cincinnati, OH.
ASSE. (1998). Dictionary of Terms Used in the Safety Profession , 3rd ed. American Society of Safety Engineers,
Des Plaines, IL.
Bird, F. E. and Germain, G. L. (1966). Damage Control . American Management Association, New York.
Boyce, A. (1997). Introduction to Environmental Technology . Van Nostrand Reinhold, New York.
Burge, H.A. (1997). The fungi: how they grow and their effects on human health. H PAC , July 69-75.
Burge, H.A. and Hoyer, M.E. (1998). Indoor air quality, in DiNardi, S.R., Ed., The Occupational Environment—
Its Evaluation and Control . American Industrial Hygiene Association, Fairfax, VA.
Byrd, R.R. (2003). IAQ FAG Part 1 . Machado Environmental Corporation, Glendale, CA.
CDC. (1999). Reports of Members of the CDC External Expert Panel on Acute Idiopathic Pulmonary
Hemorrhage in Infants: A Synthesis . U.S. Centers for Disease Control and Prevention, Atlanta, GA.
CCPS. (2008). Guidelines for Hazard Evaluation Procedures , 2nd ed. American Institute of Chemical
Engineers, New York.
Search WWH ::




Custom Search