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RE: Conversion of Exposure to Dose
Hello, Leo
You are correct here. I use the 0.7 factor for "gamma rays of moderate
energy" to convert this. Which means - estimating dose from the mineral
lying about - I use it, from Co-60 etc. at the industrial gauge - I don't.
The factor of 0.7 is from some UNSCEAR report (cannot tell exactly - it's
probably here somewhere..., I think - 1993 report)
Cheers
Nick
Eneabba, Western Australia
http://www.eneabba.net/ <http://www.eneabba.net/>
-----Original Message-----
From: Leo M. Lowe - SENES Consultants Limited
[mailto:llowe@senes.on.ca]
Sent: Thursday, 30 May 2002 06:24
To: radsafe@list.vanderbilt.edu
Subject: Conversion of Exposure to Dose
In recent messages, some people in converting from the "old"
units to SI
units assume a one-to-one relationship between exposure in R
and rem (or
0.01 Sv). For example, an instrument reading an exposure
rate of 100 mR/h
is stated as being the same as 100 mrem/h or 1 mSv/h - this
is incorrect.
The conversion depends on the gamma energy and irradiation
geometry because
of self-shielding by the body. For example, for gamma
radiation from
uranium-series radionuclides in the ground, the relationship
is
approximately 100 mR/h = 60 mrem/h = 0.6 mSv/h, where the
mrem and
mSv units are effective whole body doses i.e. the doses
that are usually
cited in regulated radiation limits.
Survey meters that read in units of mrem/h or mSv/h often
don't make this
distinction. In fact, they can't for all circumstances.
At best, they
can give tissue equivalent dose rate (e.g. plastic
detectors), but not the
effective whole body dose.
Leo M. Lowe, Ph.D.
Principal, Senior Health and
Environmental Physicist
SENES Consultants Limited
121 Granton Drive, Unit 12
Richmond Hill, Ontario
Canada L4B 3N4
Tel: (905) 764-9380
Fax: (905) 764-9386
e-mail: llowe@senes.on.ca
WWW: www.senes.on.ca
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