Radiation Report

As of 12 noon Tuesday (11 pm Monday EDT), radiation in Tochigi City near my office 178 km (111 mi) from the Fukushima Daiichi plant remains far below the level in Wednesday’s report at only 0.153 microsieverts per hour (μSv/hr). Recent history of this measurement:

• 0.224 μSv/hr Mar 16 at 12 pm
• 0.216 μSv/hr Mar 16 at 4 pm
• 0.195 μSv/hr Mar 17 at 10 am
• 0.189 μSv/hr Mar 17 at 4 pm
• 0.183 μSv/hr Mar 17 at 11 pm
• 0.175 μSv/hr Mar 18 at 8 am
• 0.172 μSv/hr Mar 18 at 10 am
• 0.165 μSv/hr Mar 18 at 7 pm
• 0.148 μSv/hr Mar 19 at 7 pm
• 0.133 μSv/hr Mar 21 at 9 pm
• 0.153 μSv/hr Mar 22 at 12 pm

I’m lucky to count among my readers a person at the US Department of Defense who must remain anonymous because he does not have permission to speak for the US government in this situation. Respecting that, I can share with you that he told me his degree is in radiological physics and that his “expertise involves radiation protection and exposure.” Given that, I’ll refer to him as Ray. He’s the sort of guy we want around at a time like this.

Looking over my recent reports sharing the above info, Ray wrote:

Those steadily decreasing exposure rates are too consistent to be due to lucky winds. It’s hard to know but, as you say, it looks promising. The low level but widespread contamination will likely be your biggest radiological concern before too long. That will very likely quickly become more of an economic concern than a true health and safety concern because low-level-dose effects is a gray area and the contaminants are complex/expensive to analyze at low levels, and difficult to clean up.

He suggested perusing the dedicated Fukushima page at the Health Physics Society, the professional group for specialists in radiation safety, and passed along that the US Nuclear Regulatory Commission allows radiation workers to receive up to 5 Rems (50,000 μSv) per year, as shown in this figure:

The current 0.153 μSv/hr level of exposure equates to just 1,340 μSv per year — only 3 percent of the US NRC allowable limit. That’s comforting news for everybody living near the situation or with loved ones near the situation. We’ll get through this.

The following radiation dose chart from XKCD, forwarded to me by my Uncle Ken and several other kind souls, puts current exposure levels in perspective:

Finally, don’t miss the Layman’s Intro to Radiation by Ellen McManis, a senior reactor operator at Reed Research Reactor.

Bottom line: all of us in the Tokyo area are going to be fine.