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

Jaro Franta jaro_10kbq at videotron.ca
Wed Aug 21 13:56:43 CDT 2013

Thanks Jim,

Its important to get to the bottom of this bizarre dose rate reporting.

Here's why: According to Reuters,

“Water in the latest leak is so contaminated that a person standing close to
it for an hour would receive five times the annual recommended limit for
nuclear workers.”


......how on earth does one get "five times the annual recommended limit for
nuclear workers" from an external beta dose ?
......and how does one even calculate a dose rate in mSv/h from an
instrument reading of beta radiation in the environment ?

Jaro in Wonderland

From: Jim Hardeman [mailto:jim.hardeman at gmail.com] 
Sent: August-21-13 10:49 AM
To: jaro_10kbq at videotron.ca
Subject: Re: [ RadSafe ] Dose conversion in beta exposure readings at
Fukushima Daiichi ?

Jaro --
My GUESS is that what TEPCO is talking about isn't an actually dose rate
MEASUREMENT, but a dose rate ESTIMATE performed with some sort of GM tube /
counter with a removable beta shield -- something like the old HP-270 "hot
dog probe". Seems to me that they're simply reporting open window readings
as "beta + gamma" and closed window readings as "gamma". I doubt they're
doing much in the way of making beta dose rate conversions.
My $0.02 (US -- don't know what that is these days in Canadian)
Jim Hardeman
jim.hardeman at gmail.com

On Wed, Aug 21, 2013 at 10:35 AM, Jaro Franta <jaro_10kbq at videotron.ca>
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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