[ RadSafe ] Dose conversion in beta exposure readings at Fukushima Daiichi ?

Jaro Franta jaro_10kbq at videotron.ca
Wed Aug 21 09:35:24 CDT 2013

Here's a question about exposure/dose rate numbers reported by Tepco at the
FD contaminated water storage tank farm earlier this week.

A picture from Tepco's pdf document is linked below.

Of interest are the sample analysis results for "Leakage water" in the table
at bottom left, reported in Bq/cm3:  Note especially the "All beta" figure
of 8.0E+4 figure.

The curious part is the table at right, which lists dose rates at various
points around the site in mSv/h - for either "beta + gamma" or gamma alone:
the highest number being ">100 mSv/h" for "beta + gamma" at point #1, and
similar values for points 10, 11, and 12.

My question is how does one apply dose conversion factors to instrument
readings, to derive "beta + gamma" dose rates in mSv/h ? ..which look to be
mostly beta, if one deducts the gamma-only number in the right column.

This is clearly not a case of committed dose due to radionuclides absorbed
in the body. So what is it ? ..if its simply a conversion of instrument beta
particle count rate, what sort of conversion factor would one apply to betas
from tritium, to get mSv/h ?

And although its not explicitly stated, the activity numbers in the lower
table suggest that much of the 8.0E+4 Bq/cm3 activity is tritium, with very
low beta energy (this water was used for cooling the damaged reactors, and
circulated in a closed loop through filters that remove much of the fission
products, but not the tritium..)

Tepco report slide:




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