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Brent,
Radsafers,
Tut-tut, wait a second or 1/Bq! Units seem
to indicate that time has become radio-active? No wonder some want Curies
forever. Do not scramble concepts and units. If you ask an astronaut what did
he/she weigh up there, they could truthfully say that they experienced a total
loss of weight (SI unit Newton), but surely not of mass (SI unit kg).
There was a time when the engineers had lured us into units like kg force, but
thankfully SI has untangled the mess. The fact that common language
has unscientific remnants of muddled thinking should not keep us in
bondage. Stating your weight, in stead of your mass, in kg, may be
excused for a year or two. Of course SI is not fully decimalised, due to
the time units larger than a second. Could that be sufficient to satisfy
the anti-decimal clan?
As far
as RP units go, most of us are not made of air, so the roentgen has its
limitations in applicability. If you use an inappropriate measuring
device, you need to make a careful calibration in terms of the quantity you are
after and be aware of the limitations. The ICRU has developed a number of
'operational' quantities in terms of which appropriate pieces of equipment can
be calibrated for quantifying external dose (e.g. Ambient dose equivalent
H*(10), Personal dose equivalent, etc). The ICRP, on the other hand, has
defined its 'protection' quantities (e.g. Effective dose E) as the weighted sum
of equivalent doses to various tissues (organs) so that it is not amenable to
direct measurement. It is a bit of a joke that dose limits are mostly
defined (e.g. by the IAEA and most member states) in terms of non-measurable
ICRP units, and it is not even mentioned in the small print that measurements in
terms of ICRU quantities are accepted as equivalent. The results of
extensive modelling in ICRP 74 illustrate how similar and different
the quantities can be. Own musings.
Chris Hofmeyr
-----Original Message-----
From:
Rogers Brent [mailto:rogersb@epa.nsw.gov.au]
Sent: 09 April 2003
05:32
To: 'Ivor Surveyor';
radsafe@list.vanderbilt.edu
Subject: RE: Subject: RE: Bq soon
[Scanned]
A
question for the pro-SI crowd.
How do you reconcile using a standard ion chamber type radiation
detector that reads out in microSv / hr, and recording that reading as the
exposure level? (I hope your
answer doesn’t include a discussion of quality factors. Regardless of what you may know about
beta & gamma radiation, the meter ain’t displaying microSv /
hr)
I
think this is my main discomfort with using SI units in that there is no
useful conversion for Roentgens.
If you are TRULY a proponent of SI, you should have a meter that reads
out in Coulombs / kg-hr (or metric subunits thereof), and then try to work
with that unwieldy number. Or
else only use tissue equivalent meters.
-Brent
Rogers
P.S. How many of you express your weight in
Newtons?
-----Original
Message-----
From: Ivor
Surveyor [mailto:isurveyor@vianet.net.au]
Sent: Tuesday, 8 April 2003 6:38
PM
To:
radsafe@list.vanderbilt.edu
Subject: Subject: RE: Bq soon
To a
person living outside of the USA it is a matter of amazement to find the
bizarre combination of units used in American texts. For instance on a
single page of a recently published text on Radiation Protection [ J. Shapiro
4th Edition] I found the student had to contend with a plethora of
units.
On page
361: Ft; Ft^2; Ft/min; Ft^3/min; cm^3/day;
pCi/cc; microCi/cc; mCi; MBq
Or on page
372: 1 acre = 4,047 m^2; 1km^2 = 247 Acres; pCi/m^2-s
and a reminder
to multiple mCi by 37 to obtain MBq, and pCi by 0.037 to convert to Bq; or Ci
by 37 to obtain GBq.
Though out the book there is a continuous need to
convert Sv to rem(s); Gy to rad(s); length in cm, ft or m and so
on.
By the way in strict SI there is no place for the cm,
cc, or cm^3. or use of "pleural forms for
units.
I
just wonder how this irrational jumble of old and new units is
tolerated. Surely more then one "Mars probe" must have gone
astray, because of this confusing jumble? I suspect that more then
one author has developed a severe "headache" from proof reading of
texts. The high quality of many American texts and publications
are such as to have a great appeal to international
readers What a waste of intellectual effort is
expanded in converting backwards and forwards from one system to the other, as
one reads and studies papers, text books, or regulations.
I am not aware of any real problem in Australia or UK when we adopted
the SI system, except perhaps a feeling of joyous relief.
Ivor
Surveyor [isurveyor@vianet.net.au]
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