Saturday, September 29, 2012

しょうゆ Soy Sauce

Posted on September 27, 2012

purchased in a local grocery store. The soy sauce was labeled as a product of Japan. No radioactive isotopes were detected that can be traced to the reactors at Fukushima. For comparison, the activity concentration of Potassium-40 (K-40) in the sample was approximately 100 Bq/L.

Collection Time(採取日): 8/21/2012
Sample Volume(サンプル量): 1.08 liters
Counting Time(測定時間): 514,760 sec.
Energy Resolution(エネルギー分解能): 2 keV (at 1461 keV)
Cs 134 Less Than MDA (0.29 bq/kg)
Cs 137 Less Than MDA (0.32 bq/kg)

Seaweed Sample Spectrum
Seaweed Sample Spectrum

Collection Date
Sample Volume
1.08 L

"MDA" is the estimated minimum detectable activity for a given isotope in the detector.


(English translation follows below)




About internal exposure from Natural Radiation
Source from "Atomic Bomb and Nuclear Power Plant"
written by Eichiro Ochiai

K-40 and C-14 exist inside of every creatures including human, as they are essential for us. They always exist in our body. In human's body,  potassium exists 2200ppm, 2.2g/kg. 93% of them are K 39 which is nonradioactive, and about 0.012% are K40 which emits β radiation. There are 2.6 x 10-4 g of K-40 per 1kg. It means 66Bq radiation are emitted per second, which can be converted to about 0.17mSv/y.

Carbon is one of the main components of our organism. 194g/kg are contained in our body. 2x10-10 g of them are C-14. It can be converted to about 0.03mSv/y. Adding 0.17mSv/y of K-40 to it will be total of 0.2mSv/y. In this book, I estimated 0.7mSv/y as an annual dose of internal exposure by adding the dose from various source of other natural radiation existing on our planet. It is unclear how close this estimate is to the actual, though. The amount of radiation exposure except this 0.2mSv also varies depending on the environment and locations, so each individual's dose also vary.

He also wrote, radioactive elements of Cs and K behave similarly, but "they are different in size which may cause the different behavior in our body. "

K40 and C14 "are distributed equally in whole body", and it limits the dose of exposure per cell to very small amount. But man-made radioactivity like Cs "would not be dispersed immediately after they are absorbed in the body", and the problem is that they would stay at specific parts, which allow the cells around to get high dose of radiation.

Periodic Table


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