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

In summary: Incidentally, the iodine-131 level in the air has been dropping steadily since the early days of the Fukushima crisis, but it's still high enough to cause health problems to anyone nearby. In summary, The contamination from Fukushima Dai-ichi appears to be extensive, with surface deposition ofCs-137 at a rate of 10^7 Bq/m^2. This amount of radiation would be equivalent to a yearly dose to a person of 467,000 µSv. The area must be evacuated for many generations, and the surface could be removed and quarantined to reduce exposure.
  • #1
helmut
3
0
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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  • #2
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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  • #3
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
 
  • #4
  • #5
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.
 
  • #6
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.
 
  • #7
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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FAQ: How to transform surface deposition in Bq/m^2 to dose equivalent rate in µS/year

What is surface deposition?

Surface deposition refers to the amount of radioactive material that has been deposited on a surface, such as soil or a building, from a nuclear event.

What is Bq/m^2?

Bq/m^2 is the unit of measurement for surface deposition, specifically for the amount of radioactive material in becquerels (Bq) per square meter (m^2).

3. What is dose equivalent rate?

Dose equivalent rate is the measure of the amount of radiation received by a person in a given period of time. It is typically measured in microsieverts (µS) per year.

4. Why do we need to transform surface deposition to dose equivalent rate?

Transforming surface deposition to dose equivalent rate allows us to understand the potential health risks associated with the amount of radioactive material present in a specific area. This information is important for determining appropriate safety measures and for assessing the impact of a nuclear event on human health.

5. How do you calculate the transformation from Bq/m^2 to dose equivalent rate in µS/year?

The transformation from Bq/m^2 to dose equivalent rate in µS/year can be calculated using the following equation: dose equivalent rate (µS/year) = surface deposition (Bq/m^2) x conversion factor. The conversion factor varies depending on the type of radioactive material present and the characteristics of the area. It is typically provided by regulatory agencies or can be calculated using specific equations and models.

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