Evening star., 1950-08-23
Explosion Effect Hinges
On Atomic Bomb Weioht
Commission Experts Report
On So-CuIIed Critical Size
By Thomas R. Henry

An atomic bomb must contain .
minimum Of 1,000, ,000, 900 .000, ,000, ,000..
OO0, 900 uranium or plutonium atoms.
These weigh approximately % pounds.
Such is the minimum weight Of the ex-
plosive material In an atomic bomb to
produce the energy equivalent Of 10000
tons Of INT, the announced power OF
the first bombs dropped on Japan. This
is equivalent to the daily output Of
Hoover Dam but is millionfold less
than the energy Of a major earthquake.
The figures are published In the re.
port of group Of Atomic Energy Com
mission experts on the effects Of atomic
weapons.
Actually, 1t can be assumed, the weight
must be considerably greater than the
minimum. It has been estimated-there
are no official figures-that large num-
Der Of the fashionable atoms in any bomb
structure will not explode.
Better Bombs Now.
The atom bomb Of the type used over
Hiroshima and Nagasaki-there pre-
sumably are somewhat better ones now,
but this is the kind on which all pub
lished descriptions are based-can be
very little larger or smaller than 1t was
at the beginning and still remains.
Whatever increase in effectiveness is
attained Is In getting more atoms to
explode.
The so-called critical size remains a
zealously guarded secret. although it
must have been worked out Independently
by the Russians. II the bomb is
smaller than this critical size, the neces-
sary chain reaction Of atom splitting
will will ha
plosion. If 1t is too large, there are
likely to be small premature explosions
which will do little damage and can be
considered "fizzles."
Once the chain reaction is started, the
report points out, the time required to
produce the explosion is about Q mil
lionth of second.
4
It would require at least T75.o00
atomic bombs to poison the surface Of
the earth with radioactive material so
that 1t would be dangerous for human
habitation.
This is the calculation Of Atomic
Energy Commission experts in report
recently issued. Some predictions have
been made that full-scale atomic war
with the poisonous dust from the blasts
SGLGl1IlS cbCAS SWA4CAC "OAAN
make the planet uninhabitable.
Much of the concern has been over
the residuals Of the synthetic element
plutonium, which is the major ingre-
dent of the bombs Of the type which
have been exploded to date. Plutonium
atoms would settle over the earth. They
would be taken up by vegetation and
eaten by men. The exploding atoms
would settle in the bones.
But, assuming the plutonium from one
bomb were distributed evenly over the
earth, there would be less than a tenth
of billionth Of gram per pound Of
SOIL Seven hundredths Of millionth
of gram per year Is a perfectly safe
dose for human being.
What Calculations Show.
Using these figures, the calculations
show that the dropping Of about TO-
100000 bombs would be required before
there would be need for any general
concern. f@s 7.'t57 E59Ed1
But there are many other dangerous
radioactive isotopes which permeate
the atmosphere after an atomic blast.
Eventually, it might be assumed. they
would be distributed pretty generally
over the face of the planet and add to
the danger Of the plutonium.
This cuts about tenfold the number
of bombs necessary to make the earths
surface uncomfortable. If not actually
dangerous to all life. The calculations
are made for six months after the bombs
were exploded.
The decrease would be very marked
from that time on.