fame eeltae
RADIATION STANDARDS, INCLUDING FALLOUT
15
alter the situation of the past few years. This is true in spite of the
fact that the level of research effort in this area has been steadily
increasing over the past decade.
.
Some operational improvements have been introduced, some few
numbers have been changed and some improvements have been made
that recognize the past apparent confusion in the relationships between
occupational and nonoccupational exposure to radiation.
;
I say apparent confusion, because do not believe that the major
rotection
bodies have ever really failed to recognize the differences
tween these two major groups of exposed persons. However, it has
been evident that they failed to give proper emphasis to these distinctions in their public writings. This omission is being rectified, we
hope.
Bart of the reason for the slowness of distinguishing between popu-
lation and radiation worker groupslies in the fact that it has only
been in the past few years that the entire population has had to face
the possibility of widespread radiation exposure, as for example from
fallout. While not devastating, or even serious, in its potential harm
at present levels, it cannot be regarded as unimportant, since it does
not carry with it the direct benefits of say, medical X-rays.
I will mention briefly a few of the factors that have been developed
in the past 2 or 3 years—thelist is not intended to be complete as I
am sure that others will bring out additional points. The Federal
Radiation Council has introduced a new term to lend emphasis to the
long-recognized fact that radiation protection standards cannot be
specified rigidly as “go, no go” limits above which there is risk and
below which there is no risk. They use the term “radiation protection guide” in place of “maximum permissible dose.” They also
emphasize the fluidity of our knowledge by expressing their guides
in ranges of values. The upper value of the middle range corresponds
to the MPD as recommended for someyears by the NCRP. This is an
innovation mainly in directing attention to the nonrigidity of our
standards, but for practical purposes control agencies will still have
to adhere to the general MPD concept.
The terms such as MPD, guides, etc., were discussed at length in
the ICRP meetings held in Stockholm last month. They have agreed
to continue the use of the term “MPD”for occupational exposure but
will avoid its use in reference to nonoccupational exposure. Noagreement was reached on a suitable term for use in reference to population exposure. They also preferred not to use the “exposure range”
concept, feeling that it was too easily open to misinterpretation. The
terminology in this area has been under discussion for 30 years. If
you have a will to misinterpret, you can do so with virtually any
term that you can invent.
The problem of additivity of radiation dose and effects has been a
matter of concern for many years. Howdo you add theeffect of risk
of an X-ray and neutron exposure to a given organ if the absorbed
dose for each is known? How, even, do you define and add the
doses? This has been accomplished by modifying the physical dose
measurement by a biological factor knownas the “relative biological
effectiveness” or RBE. At best, this has been a shaky procedure.
Attention was focused on the problem 5 or 6 years ago at which
time the NCRP established a new committee to study it. More recently the ICRP has set up a similar committee and in fact the two