Re: Tokaimura doses

[fbronson@canberra.com]

Susan Gawarecki wrote:
"Did they test "control" coins also?  Is there any Zn-65 content in the
average non-irradiated 5-yen coin?"

Jim Dukelow wrote:
"They collected 5-yen coins (with 37% zinc content) from various locations
around the Tokaimura facility and measured the Zn-65 resulting from neutron
irradiation of the coins.  Inferred neutron doses to the coins were
calculated using the transport codes DOT and MORSE and converted to ambient
dose equivalents (mSv) of 220mSv at 100 meters, 6 mSv at 350 meters, and
1.8 mSv at 550m.

Now, I'm not so sure that doses and contamination were trivial."
-----------------

My reply:

After the IRPA meeting in Hiroshima, I attended a VERY interesting workshop
on the JCO criticality accident. The workshop was organized by the Japan
Health Physics Society. One of the speakers [Komura, from Kanazawa Univ.,
plus 4 others] talked about Au-198 activation in gold jewelery.  The
measured values correleated well with distance, and with a neutron
transport code calculation.  The induced activation from the JCO accident
equaled the natural environmental neutron production value at approximately
2000 meters from the site [in the direction presented]. Of course, they
needed a quite sophisticated measurement system to detect these low
activities, especially from 1000m out.  They also measured activated Hg
from a thermometer at 600m from the source.  Other speakers talked about
Na-24 activation in soil and people, which were quite easily measured
hundreds of meters from the source.

However, given the good instrumentation available today, being "easily
measured" doesn't necessarily correlate to a "non-trivial"
dose/contamination, at least in our technical eyes.  However, in the
general public and new media, I suspect that it does.

frazier




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