by Gregory Walker
It was sobering to stand in the room where the plutonium "pit" was
assembled and think of the men who worked here 50 years before. The Pit
Assembly (G-1) team consisted of M. G. Holloway, P. Morrison, R. F.
Bacher, R. E. Schreiber, H. K. Daghlian, L. Slotin, B. D. McDaniel, and
C. S. Smith. P. Morrison was Philip Morrison, the well-known physicist
who still writes a column for Scientific American magazine. Within a
year of Trinity, both Harry Daghlian and Louis Slotin would be dead from
massive over-doses of radiation. These "criticality accidents" were
caused when the plutonium cores they were working on started an
uncontrolled fission chain reaction.
The "Dragon Experiment" was the first attempt to create a temporarily
critical mass of fissionable material by sliding a slug of Uranium-235
hydride through a larger mass of the same substance. These manual
experiments continued with the hemispheres of plutonium used in the
Trinity test bomb, the Fatman, and the bombs used at Operation
Crossroads in 1946. There were numerous "criticality accidents" with
run-away output of energy and radiation. Within a year of the Trinity
test, these accidents would claim the lives of two members of the team
that assembled the plutonium core at Trinity: Harry Daghlian and Louis
INADVERTENT SUPERCRITICALITY RESULTS IN DEATH
Los Alamos, N. Mex., May 21, 1946
A senior scientist [Louis Slotin] was demonstrating the technique of
critical assembly and associated studies and measurements to another
scientist. The particular technique employed in the demonstration was to
bring a hollow hemisphere of beryllium around a mass of fissionable
material which was resting in a similar lower hollow hemisphere.
The system was checked with two one-inch spacers between the upper
hemisphere and the lower shell which contained the fissionable material;
the system was subcritical at this time.
Then the spacers were removed so that one edge of the upper hemisphere
rested on the lower shell while the other edge of the upper hemisphere
was supported by a screwdriver. This latter edge was permitted to
approach the lower shell slowly. While one hand held the screwdriver,
the other hand was holding the upper shell with the thumb placed in an
opening at the polar point.
At that time, the screwdriver apparently slipped and the upper shell
fell into position around the fissionable material. Of the eight people
in the room, two were directly engaged in the work leading to this
The "blue glow" was observed, a heat wave felt, and immediately the top
shell was slipped off and everyone left the room. The scientist who was
demonstrating the experiment received sufficient dosage to result in
injuries from which he died nine days later. The scientist assisting
received sufficient radiation dosage to cause serious injuries and some
permanent partial disability.
The other six employees in the room suffered no permanent injury.
The preceding was excerpted from and is copyright © 1996 by Gregory Walker.
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