How to transform surface deposition in Bq/m^2 to dose equivalent rate in µS/year

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Discussion Overview

The discussion revolves around the transformation of surface deposition measurements of Cs-137 in Bq/m² to dose equivalent rates in µSv/year, particularly in the context of contamination following the Fukushima Dai-ichi nuclear disaster. Participants explore the implications of these measurements for public health and safety, with a focus on the potential need for long-term evacuation of affected areas.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Helmut presents an initial calculation of dose equivalent rate based on surface deposition data, expressing uncertainty about the validity of his approach.
  • Helmut's original calculation yields a dose equivalent rate of 467,000 µSv/year, which he finds concerning.
  • One participant acknowledges Helmut's approach as a reasonable first step but points out a potential error in the groundshine coefficient, suggesting a revised dose equivalent rate of approximately 174,000 µSv/year.
  • Another participant suggests comparing the Fukushima contamination map to the Chernobyl map to understand the severity of the situation without complex calculations.
  • Discussion includes concerns about the long-term implications of contamination and the potential for areas to remain uninhabitable for generations.
  • Participants note the lack of clear communication from authorities regarding the timeline for cleanup and return of residents to contaminated areas.

Areas of Agreement / Disagreement

Participants express varying levels of concern regarding the dose rates and the implications for public health. There is no consensus on the long-term safety of the affected areas or the adequacy of current cleanup efforts.

Contextual Notes

Participants highlight the dependence on specific coefficients and the need for accurate data in calculations. There are unresolved questions regarding the actual exposure duration and shielding effects that may influence the dose rates.

Who May Find This Useful

This discussion may be of interest to individuals concerned with nuclear safety, public health, environmental science, and those following the aftermath of the Fukushima disaster.

helmut
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Dear forum,
DOE and MEXT (Japanese Ministry of Education, Culture, Sports, Science and Technology) have pulished the results of common airborne measurements of the http://www.mext.go.jp/component/english/__icsFiles/afieldfile/2011/05/10/1304797_0506.pdf" inside the 80 km zone of Fukushima Dai-ichi NPP. A geographic map shows that the most contaminated area stretches out from the NPP to north west measuring approx. 20 km * 7 km. The measured order of magnitude of the Cs-137 Surface Deposition there is SD = 10^7 Bq/m^2.

I have tried to figure out what this contamination means in terms of dose equivalent rate in µSv/year. My approach is as follows: Health Canada have published an http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/dose/largetable-longtableau-eng.php" of GC = 1.48*10^-15 (Sv/s)/(Bq/m^2).

The product SD*GC leads to a Dose Equivalent Rate DER = SD*GC = 1.480*10^-8 Sv/s = 467,000 µSv/year.

MEXT use an upper limit of radiation dose rate permitted for people who engage in emergency work of 250,000 µSv/year which is obviously much higher than the value poeple should be exposed to in their living area. The Cs-137 half life is 30.2 years. So my conclusion is: The mentioned area has to stay evacuated for several human generations.

This is my very first assessment trial in the field of nuclear radiation and I feel very uncertain if my approach is of any meaning. I would desperately whish there is a massive misconception in my calculation. So I kindly ask an expert to falsify or modify it, or -if inevitable - confirm it.

Kind regards
Helmut
 
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helmut said:
Dear forum,
DOE and MEXT (Japanese Ministry of Education, Culture, Sports, Science and Technology) have pulished the results of common airborne measurements of the http://www.mext.go.jp/component/english/__icsFiles/afieldfile/2011/05/10/1304797_0506.pdf" inside the 80 km zone of Fukushima Dai-ichi NPP. A geographic map shows that the most contaminated area stretches out from the NPP to north west measuring approx. 20 km * 7 km. The measured order of magnitude of the Cs-137 Surface Deposition there is SD = 10^7 Bq/m^2.

I have tried to figure out what this contamination means in terms of dose equivalent rate in µSv/year. My approach is as follows: Health Canada have published an http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/dose/largetable-longtableau-eng.php" of GC = 1.48*10^-15 (Sv/s)/(Bq/m^2).

The product SD*GC leads to a Dose Equivalent Rate DER = SD*GC = 1.480*10^-8 Sv/s = 467,000 µSv/year.

MEXT use an upper limit of radiation dose rate permitted for people who engage in emergency work of 250,000 µSv/year which is obviously much higher than the value poeple should be exposed to in their living area. The Cs-137 half life is 30.2 years. So my conclusion is: The mentioned area has to stay evacuated for several human generations.

This is my very first assessment trial in the field of nuclear radiation and I feel very uncertain if my approach is of any meaning. I would desperately whish there is a massive misconception in my calculation. So I kindly ask an expert to falsify or modify it, or -if inevitable - confirm it.

Kind regards
Helmut
One's approach is a reasonable first step. It indicates a problematic area. It is a relatively high dose rate to which to be exposed. Certainly one would want children and infants in the area.

The groundshine rate for Cs-137 is 5.51e-16 Sv s-1Bq-1m2, whereas 1.480*10-8 is for Cs-134 (t1/2 ~ 2 yrs).

Of course, the cumulative dose over one year is subject to the actual duration someone is exposed to that level of activity. This would be a concern for someone in agriculture who would spend 8-16 hrs/day in a field where such activity is found. Otherwise, one then has to consider shielding, such as dwellings. Likely the surface could be removed and quarantined. The ground could be turned over to reduce exposure.
 
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Astronuc said:
One's approach is a reasonable first step. ...

Thank you for your quick response! And sorry for my wrong ground shine coefficient value!
The corrected result for the Cs-137 Dose Equivalent Rate now is approx. 174,000 µSv/year. A relief but not a comfortable one.

Kind regards
Helmut
 
Thanks! It is now even clearer to me that Japan has become a bit smaller in area. Obviously I have missed something in the media since March. Loss of territorry for more than a decade (?) is worthwhile to mention more than once in the news.
 
helmut said:
Thanks! It is now even clearer to me that Japan has become a bit smaller in area. Obviously I have missed something in the media since March. Loss of territorry for more than a decade (?) is worthwhile to mention more than once in the news.

You have not missed anything. TEPCO is making reassuring noises from time to time about ending the cleanup and "allowing people to return to their homes" but they never give a timeline. That's about it.
 
See also
AntonL said:
Soil contamination from Fukushima crisis comparable to Chernobyl:
http://english.kyodonews.jp/news/2011/05/93120.html

(or http://www.japantoday.com/category/national/view/soil-contamination-from-fukushima-crisis-comparable-to-chernobyl-study )
 
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