Reenactment of the 1946 incident. The plutonium is hidden under a hemisphere of a reflector held by a screwdriver.
All of us in physics lessons saw a picture in which it was drawn how one piece of uranium is brought to another, as a result of which a critical mass accumulates and a chain reaction begins. American nuclear scientists made it even easier - they simply thrust a screwdriver between two hemispheres of uranium! Of course, such a frivolous attitude towards nuclear materials could not but lead to tragic consequences.
After the end of World War II, the United States continued nuclear research in the military laboratories of Los Alamos. One of the leading Los Alamos collaborators was Dr. Louis Slotin. He was engaged in experiments with a critical mass - he brought one hemisphere of uranium to another and detected the beginning of a chain reaction.
Louis didn't trust automation - so he just put one hemisphere of uranium on top of another and slipped a screwdriver between them. Because of this, the hemispheres could not come into contact with each other completely, which did not allow a chain reaction to develop.
But what happened next …
Rather, first let's see how it all began …
In 42, scientists gathered from almost all over the world in the states came close to unraveling the secrets of the structure of matter. The only thing left is to confirm the theory with practice. Fulfill the dream of alchemists to transform some elements into others.
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The pictures show the very first of the "man-made" nuclear reactors. The "woodpile" consisted of graphite blocks, which were neatly stacked, and in every second layer the blocks were hollow, and nuclear fuel was placed inside - pressed uranium oxides and metal ingots.
Graphite and 60 tons of uranium.
Since such a reactor was used to test the possibility of a controlled reaction, there were some kind of "controls" - several types of rods made of cadmium and boron steel. There were three types of rods in total. The first type was controlled from the remote control; these were control rods. The second type is emergency rods. Rather, it was the only rod that was suspended over the reactor on a rope. If an emergency arose, it was planned to cut the rope, and the rod that fell into the reactor jammed the reaction. Well, and there was also a rod, which was removed manually in order to create conditions for a controlled nuclear reaction (that is, to bring the reactor itself to a critical state).
All this is incomparable with modern reactors - neither a cooling system was provided (i.e. it was, the reactor was planned to be watered with ordinary water in case of strong heating), nor a system for protecting a person from radioactive radiation. The reactor worked for several tens of minutes (28, if accurate), and during this time, scientists received real proof of the possibility of a nuclear reaction (controlled) - the experiment was completely successful.
During this time, we were convinced that the neutron multiplication factor can be controlled! And thank God. Otherwise, in the place of Chicago, and for the experiment there was no place more interesting than under the stands of the university stadium, there would be a kind of Hiroshima. Apparently to the professors, all these blocks were folded by hand, they did not want to go far from the alma mater.
1946 year. Kurchatovsky reactor.
A little larger and more thoughtful, but it is also clear that he is folded with his hands. And in general, in those years, experimenters had not yet become infected with the bad habit of working as manipulators.
Simulation of the 1945 incident. The plutonium ball is surrounded by reflector blocks - tungsten carbide.
Another Los Alamos nuclear scientist, Dr. Richard Fineman, later wrote: "These tests were like tickling the tail of a sleeping dragon." And he was not exaggerating at all - one laboratory employee had already paid with his health for his negligence.
On August 21, 1945, a young scientist Harry Daglyan single-handedly conducted an experiment to study the reflection of neutrons. The core was placed inside a structure of tungsten carbide blocks, a neutron reflector. The addition of each new block weighing 4.4 kg (the total mass of the blocks was supposed to be 236 kg) brought the assembly closer to a critical state. While trying to install the next block, Daglyan dropped it directly on plutonium, which transferred the assembly to a supercritical state. As soon as the bar fell on the plutonium, Harry seemed to be in the center of a nuclear reactor. There was no explosion, but the scientist received an incredible dose of radiation.
Despite the fact that the block was immediately removed, Daglyan received a lethal dose of radiation (about 5-8 Sv) and died from radiation sickness 25 days later. A second person, security guard Robert J. Hemmerli, who was not involved in the experiment, was also injured during the incident and received a dose of approximately 0.2 Sv. Hemmerli died in 1978 (32 years after the incident) of leukemia at the age of 62.
During the incident, approximately 1016 fissions occurred, the nickel cover on the plutonium ball did not collapse
As it turned out, he was not the last.
On May 21, 1946, Louis Slotin, as usual, began his experiments. With a habitual movement, he shoved a screwdriver between the hemispheres of plutonium (the same ones that killed Harry Daglian). Seven other employees were present in the secret Omega laboratory, including an intern who was supposed to come to Slotin's place. As Louis performed the critical mass test, the screwdriver slipped out of his hands and the plutonium hemispheres closed.
Immediately, all eight scientists were hit by a wave of heat, and a blue glow appeared over the plutonium. The room turned out to be permeated with gamma rays and neutron fluxes - Geiger counters clicked like insane.
To Louis's credit, he was not taken aback and quickly pushed the hemisphere to the floor - with his bare hand! The nuclear explosion did not take place, but there was little comfort in that for Louis. He already felt a burning sensation in his hand and a sour taste in his mouth - he was beginning to have radiation sickness.
Louis was rushed to the hospital, but he knew that his days were numbered. Slotin sent a telegram to his parents in Winnipeg - his dad and mom arrived in Los Alamos a few days before he died.
Two years later, two more scientists who were present at the ill-fated experiment died from radiation sickness.
Louis Slotin behaved like a real hero and saved at least several people. But if American nuclear scientists thought with their heads, they would not lower the upper hemisphere to the lower one, but raise the lower hemisphere to the suspended upper one. Then, in case of careless movement, the lower hemisphere would simply fall to the floor. It was this design that was used in later experiments.
The plutonium ball was used in the ABLE nuclear test during Operation Crossroads on July 1, 1946. Thanks to the experiments of Daglyan and Zlotin, the effectiveness of the weapon used in the tests was increased compared to that used in the bombing of Japan.