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 ```what is normal sea level background radiation for the USA? Is a REM the same unit as a millirem/minute? What are the other units of radiation measurement and how do they relate to REMs? I have a new geiger counter with a pancake sensor and don't know how to read it. I am trying to learn what constitutes "normal".```
 ```The Roentgen is a unit of radiation exposure. The Rem (Roentgen Equivalent Man) ... Background radiation levels are typically around 300 millirem per year. ... millirem is 1/1000 of REM. Same as millimeter is 1/1000. meter (for basics of these prefixes, kilo, milli, see http://physics.nist.gov/cuu/Units/prefixes.html http://www.unc.edu/~rowlett/units/prefixes.html ) rem is the older unit of dose, today the SI unit for dose (Sieverts) is used (1 Rem = .01 Sieverts). http://www.nucleartourist.com/systems/rad.htm Here are SI units of related quantities there is activity of source, intensity at a given point, absorbed dose and effect http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/radrisk.html here is a less technical description of the risks: The risk from radiation exposure can be reduced by shortening the time of exposure, getting farther away from the source, and shielding or blocking the source. It is known that whole-body radiation doses of more than 10,000 millirem over a short period of time can cause a slight increase in a person's risk of developing some types of cancer years after exposure. The risk that radiation-induced cancer will develop during the person's lifetime is estimated by the National Academy of Sciences to be about 1/20 of one percent for every 1,000 millirem of short-term exposure greater than 10,000 millirem. In other words, if you were to receive a short term exposure of 11,000 millirem (11 rem), your estimated risk of developing some type of cancer would increase by 0.05 percent. http://www.slocountyoes.com/emergencyplanning/radiation.html By comparison, the dose from one chest x-ray is approximately 10 millirem. Regulatory agencies in both the U.S. and Canada have set limits for worker exposure which are considerably higher than the level of natural background radiation. In the U.S., the annual dose limit for radiological workers is 5,000 millirem (the limit for a pregnant worker is 500), while the dose to the public from nuclear industries is limited to 100. http://www.web.ca/~nwatch/nuclear_waste/health.html Average American exposure What radiation dose does the typical person receive? Several sources of radiation and the dose that each source gives to the average American each year are listed in Table 1. http://www.ag.ohio-state.edu/~rer/rerhtml/rer_23.html and here is piechart for sources: http://www.fpl.com/about/nuclear/contents/nukebook_measuring_radiation.shtml Amounts We Receive Most Americans receive about 360 mrem per year from all sources of radiation, including radon and medical exposure. About 40 mrem per year comes from the natural radioactivity in our own bodies. Most of our natural background radiation comes from cosmic radiation from outer space and from radioactive materials in the earth's rocks and soil. http://www.nuc.umr.edu/nuclear_facts/radiation/radiation.html Normal Radiation Exposure - efect of elevation At sea-level, the average radiation level is approximately 0.03 microsieverts per hour. As the altitude increases, the radiation exposure increases exponentially. Mexico City, 2240 m above sea-level, is exposed to about 0.09 microsieverts per hour; La Paz (in Boliva, South America) - the highest city in the world - has radiation of about 0.23 microsieverts per hour. http://library.thinkquest.org/C004606/applications/measuringrad.shtml and here are answers to some FAQs on measuring radiation: Civil Defense Ultimate CD Over 300 PDF files, close to 20,000 pages, totalling over 475 megabytes, with Civil Defense documents, Military Field Manuals, NBC Prep, Medical, and Survival topics. Classic books from many authors in text format and a small selection of religious books for personal research and audio files included. http://www.radmeters4u.com/index.html#7b Hedgie```