I live on the east coast of the United States in a cozy little state known as Virginia. I am extremely far from Fukashima, and yet, I have logged incidences of radioactive rain several times. Though I have read of many on the internet who seemingly record readings of 600+ counts per minute (10-40 times normal background) I normally find only slight elevations, no more than twice background, which are only decipherable to me via statistical analysis.
July 3rd, 2011 I detected a slight increase in radiation during a rain storm. From past experience with rain, I have found that monitoring at ground level, or in the rain, yields much higher results. Most of the time my Geiger Counter records data from my office, next to my window, about 30 feet above the ground. As a result, changes in radiation readings are more slight, but never-the-less, detectable.
There is most likely little reason for concern, given the slight readings and their very possible non-Fukashima origin, perhaps being the result of pollution (often beta and alpha emitter containing). Without an scintillator, it is nearly impossible to accurately determine the cause.
The radiation seems to dip rapidly upon the onset of rain, rising to normal levels during the rain and slowly building after the rain. When next I am confronted with a storm I can easily track, I will test my rain levels, wind, and other data in conjunction with my radiation monitoring.
Data on my unit:
International Medcom, Model CRM-100 (eff. RadAlert 100)
Detector: LND 712 Thin Mica Window Ne+Hal
Sorry for the low quality of the graph. My graphing software is very good with numbers, but very poor with presentation.
I tested the data from 05:10 PM, EST, 030711 until 03:44 AM, EST, 040711. The average reading was 15.23 CPM. From this I calculated a simple standard deviation and arrived at σ=3.98. This would mean that readings of 11.25< = and readings of =>19.21 would be indicative of an abnormal event. I like to treat multiple sustained readings, or a segment of greater amplitude, as a true indicator of an event.
Above is the raw data from Geiger Graph software. Note the rise in the average readings follows the rain. If you are skeptical of the rain, please look up historical data for rain fall for Fredericksburg, VA for late 030711.
Here is a link to the actual raw data.
Here is a link to my past month’s data showing my normal average of 14 CPM
June 1 – 15
June 16 – 30