Re: SI units

[mwilliam@mailbox.uq.oz.au (Michael Williamson)]

This is a subject that never ceases to amaze both myself and many other
safety professionals from the non-US english speaking world. Clearly, the
issue is really not just concerned with radiation units but extends to the
whole measurement system.

The american enthusiasm for a complex and outdated system of measurements
would be understandable if it had been devised in america, but of course it
wasnt.  Although the US system has some differences, its still essentially
the old "imperial" system of british origin.

Believe me, once you bite the bullet and start to make the change it makes
sense and after a while you wonder why it wasnt done earlier.  We changed
to basic metric (essentially the SI implementation) measurements for the
general public 20 years ago with very little resistance or real
difficulties.  Admittedly, we (australians) are probably a more compliant
people with little of the "rugged individualism" which seems (IMHO) both a
strength and a source of trouble for the US.

I know becquerels and sieverts take a bit of getting used to and its not
easy to jetison the measurement habits of a lifetime, so I'll give an
example of how change can occur: remember the old uranium and thorium
series nomenclature?  References to "Radium C''" and "mesothorium II" etc
have now virtually disappeared, even in conversation as well as in the
literature (I bet this will bring them out of the woodwork!). It was a
system that dated back to the first understandings of radioactivity and
when it became manifestly obsolete it was replaced fairly painlessly by a
system that was more consistent with the rest of  physics and chemistry.

This is what is now happening to roentgens and curies: the physics world
has moved on and the arbitrary bases of these units has been recognised.
The replacement units are ones which are consistent with the other units
used to characterise physical phenomena - which is as it should be if
health physics and radiation protection is to be regarded as a science
rather than as some obscure craft with its own unusual system of
measurement.



Michael Williamson                              ph +61 7 365 4504
Radiation Protection Adviser                    fax +61 7 365 1577
Occupational Health and Safety Unit
University of Queensland
Brisbane 4072
Australia