Background radiation readings were within the normal range from my Overland Park office for the period Saturday through Monday. See chart below.
The average exposure during this period was about 10.2 µR/hr with most measurements ranging from about 6 to 14 µR/hr.
A roentgen (R) is an older unit for radiation exposure but is still commonly used. A millionth of a roentgen is a micro-roentgen, which is abbreviated µR.
Wikipedia suggests a “typical exposure” might be about 23 µR/hr for background radiation.
A source monitoring background radiation in the Russian Far East region says background radiation there ranged from an average of 10 to 15 µR/hr at an acceptable level 30 µR/hr.
The Sievert is a newer unit for dose equivalent radiation, which was formerly measured in rem and is not exactly the same as a roentgen.
According to Steve Quayle’s page on radiation measurement units: “For purposes of practical radiation protection in humans, most experts agree (including FEMA Emergency Management Institute) that Roentgen, Rad and Rem can all be considered equivalent.” With that assumption, one can simply convert 1 microroentgen (µR) = 0.01 microsievert (µSv).
After sorting through these conversions, the Overland Park reading of 10.2 µR/hr is equivalent to about 0.10 µSv/hr.
The chart for Tokyo shows levels there reached about 0.6 µSv/hr on March 15 but have fallen back to about 0.10 µSv/hr on March 21 after being about half that at 0.05 µSv/hr for several days.
The chart for Ibaraki shows levels were about 1.6 µSv/hr on March 15 and are still elevated at 0.3 to 0.5 µSv/hr.
Charts for Fukushima are not shown but some values in the table from there are quite high with one value being 110 µSv/hr.
Japanese sources show this diagram for “Radiation in Daily Life” (or see final page in this PDF).
I’ve owned an RM-70 radiation detector from Aware Electronics for over a decade and have recorded background radiation levels in a number of places.
In general, background radiation is lower at sea level, like in Florida, and is higher at higher elevations, like in Denver. This is because a thicker atmosphere at sea level will block more cosmic radiation than a thinner atmosphere at higher elevations.
- Radiation Dose Chart
- No radiation risk to Kansas from Japanese reactors, Kansas Watchdog, March 17, 2011.
- Radiation, nuclear power, health concerns, Watchdog.org, March 17, 2011.
Contact: Earl F Glynn, editor@KansasMeadowlark.com