Tuesday, March 15, 2011

A GEIGER COUNTER BROADCASTS FROM TOKYO

Blogger's Note: I just went on the web for a crash course in Geiger counters and the limiting radiation doses recommended for humans. I found that the average annual dose from all causes received by Americans is 0.36 rem/year and the maximum yearly dose allowed for adults working in radioactive environments is 5.0 rem/year.
Then I found on the internet a real-time Geiger counter running in Tokyo (see below). All day today it has between 16 and 18 counts per minute (CPM). 
This evening the web site showing radioactivity in the U.S. came back on line. At 21:46 MST the CPMs by states were: WA 32,  AZ 19, CO 58 and 24, IN 36, NJ 22, NC 33. According to the site explanation, normal background radiation may average from 10 to 50 and the alert level suggesting an extraneous component is set at 130.  Nevertheless, translation of CPM counts into dose rates as rem per unit time requires knowledge of the type of irradiation, which must be determined by a different method. In the case of 0.66 MeV Cesium-137 gamma rays, the true dose rate affecting the human body involves multiplying the CPM by a factor of 20. So "the jury is still out" regarding whether or not the U.S. CPMs reflect fallout from the damaged Japanese nuclear reactors.


Video clips at Ustream

2 comments:

Shelia said...

Dave, is this because of fallout traveling over to Western US? What about Strontium 90? Also, what about Arizona? Are we at risk? Thanks.

éminence grise said...

Shelia, I just revised my original comments. Yes, the issue is fallout, which will very likely reach the U.S. if it hasn't already. I don't know whether strontium 90 will be in the mix. As far as I know the greatest danger is Cesium-137, of which their could be a lot if the spent fuel rods catch fire. You wouldn't want to breath any dust containing it, so get yourselves some dust masks and use them when dust is blowing. Hopefully health physicists at the national laboratories are keeping an eye on things and will sound the alarm in worse comes to worse. --Dave