Radioactivity Measurements

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During the past few days a great deal of information has come in about the amount of radiation reaching the U.S. from the Fukushima reactors in Japan. Measurable radiation has reached our shores, but thousands of times below intervention standards.

Recently, a University of Washington team presented highly sensitive results based on measuring the radioactive particles trapped by the filters for the UW Physics and Astronomy Building (their web site is

Let me show you some examples of their findings and remember the tsunami occurred on March 11. Here is a plot of the amount of radiation measured on 16 March and 17 March, based on the energy levels associated with Iodine-131. The signal is very clear on 17 March.

Here is an alternative presentation for more radioactive species. A clear signal was evident around 7 days after the tsunami, peaking a few days later, and then declining.Again, these levels, although measurable are very low and not a threat.

EPA has been actively taking samples of rainwater and milk around the country. The rainwater results, released yesterday, revealed that for most of the country the radioactivity increase was unmeasurable except for Richmond, CA, Boise, Id. and St. Paul, Mn. Boise was particularly high. WHY?

But keep in mind that we generally don't drink rainwater and I131 has a half life of eight days. By the time water is used (either percolating to the water table and entering a well or reaching the intake of a reservoir--where it has hugely been diluted--little I 131 radioactivity will be left.

A number of the media is hyping the radioactivity levels by making the implicit assumption that the relatively high values will continue for an entire year...which of course is ridiculous. A few locations in the U.S. have had some one-day spikes, but the dosage would be very low...even if you drank rainwater...because radioactivity levels rapidly drop down into the noise level.

Regarding milk, screening samples taken March 25 at Spokane, WA detected 0.8 pCi/L of iodine-131, which is more than 5,000 times lower than the Intervention level set by the U.S. Food and Drug Administration.

The fact that some of the radiation has reached the NW in minute quantities should not surprise us. Several scientists (such as Dr. Dan Jaffe of the UW) regularly measure small amounts of Asian pollution over the Northwest, particularly as specially equipped labs at Cheeka Peek (NW Washington) and Oregon's Mt. Bachelor.
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