82
DISCUSSION ON TOPIC IT
THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD
nearby it in air: whether the ground acts more
like a sink or a reflector for radiations.
To follow your suggestion, I won't make a
dissertation of it. The auswer is that the
surface appears to act as either one under
different circumstances, and apparently when
the incidence is close to grazing, as it is a large
distance froma not-too-high burst. of a nuclear
spectrum of the material after it went through
theshelter.
Dr, Teresr. I don’t know,
[ think this is
something that people have neglected.
Dr. Bonn. I think that is a very good point.
] know of no experimental data on it at all.
Tf the energy is sufficiently low, the radiation
will be less effective for the sameair dose.
on the interpolation curves, even from the
Dr. Bore. There is one point in Dr. Bond's
presentation which strikes me as being very
noteworthy, indeed, and this is his comment
about neutrons and their presumptive depth
dose curve, and the resultant biological effect.
radiations, and they in turn to some extent,
can almost be thrown away. Such a conelusion would be a surprise to some people. On
the other hand, there are some bomb effects,
weapon, the model holds pretty well.
Build-
ings, on the other hand, if they were close by,
. would probably decrease the dose over what
had been calculated for free air. As we saw
hardest components of the radiation a great
deal of the dose that is delivered at a large
distance from the bomb comes from scattered
Thus near the lethal dose range, bomb neutrons
especially the lower energy ones, do not come
from straight ahead but from the side; and
occasionally the lowest energy photons even
are back. scattered toward the bomb again. So
some large dense volume, such as a concrete
perhaps at very high doses of neutrons and
volume of this scattering source would probably
decrease the dose to some extent over that
predicted for free air.
mission of neutron effects through the whole
building, that occupied a large part of the
Dr. Crowxits. Are there any questions from
the floor?
Dr. Terust (NRDL). I would like to make a
comment concerning this energy dependence.
The comment I want to make is concerning the
biological effectiveness of energies below the
250 KVP that was presented here. J am under
the impression that for very low energies you do
have a difference in biological effect, which is
muchless than these higher energies. If this is
the case, what I would like to know is what
would be the effects of shelters; for instance,
individuals will be in shelters. Air doses will be
measured inside. Therefore, the LD-50 may
be very muchdifferent because of degradation
of energy in going through shelters. I was just
wondering whether or not you want to make
some more commentson that.
Dr. Bonn. Before I could answer that,
I would have to ask you to give me the energy
gamma reys where there is primary damage
to the cortex of the central nervous system
fairly close to the body surface. In these
instances neutrons as well as gamma rays
might be effective. Butfor cases where trans-
body is required, it looks like the self-shielding
factor that is implied by this depth dose curve
must markedly reduce the whole-bodyradiation
effects due to the neutrons. There are few
bombs where the neutron rep divided by this
factor will become very important. —
Dr. Bonn. I hasten to add, however, that
again the curves I showed were calculated
curves, and J have every reason to believe and
physicists have assured me that these would be
the worst case in the field. Again, we have no
measured neutron depth dose curvesin thefield.
Dr. Cronxirr. There is another problem of
practical importance not directly commented
on, Dr. Bond, and that is what proportion, in a
fallout field, of a dose is coming from close in
and what proportion from far out? How big
an area does one haveto clear if you are at the
center to effectively reduce the dose by a factor
of 10 or 2 or whatever you wish?
Dr. Bonn. I have seen several estimates of
this, and Dr. Robertson in our laboratory
carried out a calculation along these lines.
The
answer one gets depends to a large extent upon
the assumptions made in the calculation. It
appears definitely that at least half of the
radiation comes from 10 meters away or more.
I have seen other cstimates that most of the
radiation comes from the order of 100 meters
or more.
Dr. Bora. The method I talked about could
answer this question.
The machine calcule-~
tions, if carried further would be susceptible to
analysis in this regard. Youcould tell not only
what the 4x spectrum wasat agiven point, but
from what solid angle the radiation was coming.
If there is a general interest in this, someof the
people who generated the original material
might be able to carry the problem further.
A comparable solution can be made for the
initial gamma case: that is, a spectrum can be
generated as a function of angular distribution,
and for
penetration
through shielding this
information might also be valuable. 1 don’t
think it has ever been done, but it certainly
could be done.
Dr. Bonn. This information is of great practical value in regard to the question that was
asked, how muchof an area must be cleared.
I will say again that in termsof the depth dose
pattern obtained in the individual as we saw
under these conditions we apply the curves
corrected for inverse square. So as far as the
depth dose patterns are concerned, it does not
matter from what distances the radiation
effectively originates.
Dr. Cronkite. Are there any further questions or comments on any of the papers of this
afternoon? I notice that everybody so far has
rather artfully dodged what I still think is a
rather essential part of this symposium, to
somehow or other come along with an estimate
or guestimate of really how effective is radiation
in man. I would choose not to answer this
myself, but I see Col. Maxwell, who has had a
lot to do with fallout. After all, how can one
assess the hazardif you are not willing to comment somewhat on the effectiveness in man?
I think it is self-evident that any reanalysis of
83
the Japanese datahas (o take ina lot of practical
considerations about wherethe individuals were,
how far they were away from the bomb, how
close they were to large conerete buildings, and
so on. It may he a completely impossible
question to answer, but 1 am sure that someone
here is not so shy, other than Dr. Borg, that
they are not willing to comment on the subject.
Dr. Bora. Utilizing data concerning weapon
type, yield, burst. height, and atmospheric
density, I caleulated gamma-distance curves
for the Nagaseki bomb. Casualties have been
. reported in some detail for the Fuchi school in
Nagasaki (Oughtsozon, A. W., and Warren, S.,
“Medical Effects of the Atomic Bomb in
Japan,’ New York, McGraw-Hill, 1956, p. 68).
There were some woodensheds in that building
where apparently, as Dr. Bond and I looked it
over the other day, approximately 50 percentof
the inhabitants of the wooden buildings~-about
30 in number--died of radiation disease, and
were presumably exposed fully to bomb nuclear
radiations only. At this distance the free air
calculation that I made was 600 roentgens.
This is a weapon, whether we choose in general
to discount neutrons or not, which did not have
a large neutron contribution, If the remaining
concrete structure of the school nearby served
to decrease that dose even further, and if the
tiles androofing, evenif they didn’t accountfor
a great deal of shielding, had anyeffect, T
would say about 100 or 150 roentgens less than
600 roentgens would be the I.D-50 for man for
inilial gammaradiation. ‘The mortalityfigures
are not agoodstatistical series, I will admit.
Dr. Cronxirz. I cannot refrain from commenting somewhat further that I see people
here sitting who are responsible for writing
handbooks and who put these numbers in them.
I would not want to go so far as to call them
by name, but. possibly they would like to comment.
Mr. Linpwarm (Chemical Warfare Laboratories). Obviously the sort of question that
Dr. Cronkite is pushing for is one, is there
such a thing that can be drawn up at the pres-