ALARA? -Reply

[Charles Willis <CAW@nrc.gov>]

The ALARA concept continues to evolve, but the basic idea of keeping doses as low as
practicable has been with us for some time and, of course, the terminology has changed: at
one time the admonishion was "as low as possible."  I suspect that it goes back to the
pioneers in the 1890s but that might be difficult to document.  We do know that the NCRP
supported the idea before Worrld War II.  For example, in 1938, NCRP-4 (NBS Handbook-23)
stated:

     "The most important point is for the radium worker to have an ever present
      realization of the danger and to carry out all manipulations in such a way as
      to reduce the exposure to a minimum."

The idea that ALARA= optimization is of more recent origin.  See ICRP-22 (1973) on ALARA
and ICRP-37 (1983) on optimization.

The idea that ALARA means going to illogical extremes is seldom stated explicitly but does
make itself evident; see 10 CFR Part 50, Appendix I (1975), etc.

It was based on the recognition that we did not know the threshold for the ill effects of
radiation, or even if a threshold existed.  The first dose limits were simply based on
Mutscheller's observations of what good practice could achieve in 1934.  It seemed logical to
keep doses as low as practicable.  Today, ALARA is commonly tied to the "linear,
no-threshold hypothesis," which seems to date from some German work in radio-genetics of
about 1930.  The idea of tying ALARA to optimization  grew out of the recognition that things
were being carried to illogical extremes and that some pallitable means of backing-off was
needed.

A geat deal has been published.  Lauriston Taylor's "Radiation Protection Standards" might be
a good starting point.  Of course, I have to recommend the Brodsky-Kathren-Willis article in
the November 1995 Health Physics Journal.

It is an interesting issue.  Have fun with it.

Charlie Willis