First, There has been a run on Potassium Iodine tablets in the western United States. These sales of Potassium Iodine may be the result of some misinformation being disseminated on the Web and some radio programs that offer survival products and supplements as part of their revenue source. The folks transmitting the graph have a basic misunderstanding on radiation levels and terms used to relate them.
The graph making the rounds that shows radioactive fall-out coming from Japan to the Western United States is shown below.
The graph misrepresents the current situation on the ground and appears to be transmitted for secondary gain other than informing the public of a potential danger. The Graph uses “Rad” measurements. The graph states that the West coast of America will receive 750 Rads 7-10 days after the accident that occurred in Japan
If you have listened to NHK (Japan Television and Radio) you have heard the measurements being expressed in Sieverts not Rads. So how do Sieverts and Rads compare. This is where I think the Graph is being used to intentionally confuse folks. In most text books you will not see a side by side Rad, Sievert comparison on a chart. One will find a comparison with another term the Rem. 100 Rem = 1 Sievert. So how can one convert Rads to Rem to get Sieverts? There is no easy mathematical formula to do that and that is why the continued use of the rad is “strongly discouraged” by the author style guide of the U.S. National Institute of Standards and Technology
So using the Rad in the chart when Sieverts are being used can only confuse the reader into a conclusion that advances the writers’ agenda. To find out the agenda, Like the all saw goes, especially in Politics, follow the money.
Just for argument in some cases a 1 Rem has been identified as 1 Rad when 1 Rem x 1(Q) = 1 Rad for X-rays
Currently at the site the emission maximum is 400 uSV/H or 0.4 MSV/h or 0.0004 Sv. The reading can alse be expressed as 40 Millirem or in our 1 mathematical case 40 MilliRads. Nausea and vomiting generally occur within 24–48 hours after exposure to mild 1000000 uSv (1Sv) doses of radiation. The chart relates that 750 Rads will pass over the Western United States in 7 to 10 days. That means that there will be no less than 7.5 Sieverts in America. That can’t and won’t happen, the figure in America cannot be higher than the readings at the reactor site. The graph shows levels that would cause death to nearly everyone in the West Coast.
I think the best way to express exposure levels at the reactor site being 400 usv/h and what exposure levels would look like at certain distances could be compared to a radio station transmitter and a radio receiver. A local Radio station may put out 5000 watts of power but by the time it gets to your radio receiver it may be 1 micro-volt a (very tiny amount of power). That is why radios have amplifiers. They need to make that tiny signal load enough to convert it to sound you can understand.
When I worked at a small radio station we had only 400 watts of power. We had to shield everything in the radio room in order to keep the radio frequency out so it would not cause feedback in our system. That strong signal would cause a mess to our equipment if we didn’t have the radio room shielded. Each day after work I would drive home, some twenty miles away, and listen to the station slowly fade away until it was gone. I couldn’t hear my own station when I was off work. I lived too far away that 400 watts could not make it to my home only 20 miles away.
Like the radio station, The 400 usv/h at the site will fade more and more as you drove away. The reading would diminish to nearly unreadable after a set distance from the Reactor.
I am sure that someone who has a science background will mention that my comparison with radio waves and radiation is incomplete as it deals only with Gamma and X-Ray radiation not particles. That is correct, as with all analogies, the comparison breaks down with very close comparison, but the basic idea is the same. Radiation levels diminish by many factors with distance.
The Rest of the Article comes from BBC and a few other links deal specifically with the Term Sievert and potential danger from nuclear radiation:
- Fukushima Radiation Update (news.sciencemag.org)
- “Fast Facts about Radiation” (economistsview.typepad.com)