I feel that unless history is widely reviewed and understood, it will be repeated. On that premise I will make a very solemn post today on a subject I think is easily forgotten, but has extreme significance in our world. But first, some history.
In early 1939 the first uranium fission experiment was successful, and much excitement in the scientific community followed. It became obvious that self-sustaining nuclear chain reactions were possible. Six months later Leo Szilard, prompted mostly by presidential aide Alexander Sachs, persuaded Albert Einstein to write a letter to President Roosevelt explaining the potential use of uranium in an outrageously powerful new weapon. On August 2nd that letter was sent, but it didn't have very much initial impact. A little over two years later on December 6th, 1941, the United States started research in earnest into what became the Manhattan Project.
Nearly a year later on December 2nd, 1942, the first man-made self-sustaining nuclear chain reaction occurred using lots of Uranium-238 and graphite for a moderator. It was basically a big pile of black bricks and wood set up in a fairly spherical layout on a squash court at the University of Chicago. Control rods coated with cadmium were used to absorb extra neutrons until the experiment was ready to begin. The mass of uranium was carefully brought to criticality (in other words it was self-sustaining) by partially removing the control rods, and ran for a little more than a half hour, generating lots of heat and neutrons. The atomic era was now set to unfold quickly.
During the war it was feared that Nazi Germany was pursuing an atomic weapon because it stopped selling uranium from Czechoslovakian mines, so work intensified in America to discover the secret behind prompt-critical nuclear energy. There are actually four stages of criticality possible in fissile material, and prompt-critical is the state a nuclear weapon uses for a very brief moment before exploding:
||Neutrons being absorbed by fissile material do not themselves give off enough additional neutrons to sustain a reaction
||Just enough neutrons are being generated to provide a self-sustaining reaction. Once online, nuclear power plants operate in this realm.
||More neutrons are being generated than are necessary to have a self-sustaining reaction, so the rate of the reaction is increasing
||When supercriticality can be maintained solely from “fast neutrons”, which are very short-lived, but have a much higher energy potential than the normal “free neutrons” or “thermal neutrons”.
After experimenting in the lab with critical masses of uranium, it was determined that if you have about 140 pounds of uranium in a sphere, of which 80% is enriched to be the more fissile U-235, a prompt critical reaction will quickly follow. On August 6th, 1945 the Little Boy device was dropped over Hiroshima with that configuration. When it was a quarter-mile above the ground two seperated parts of Uranium were rapidly combined in the device inside a thick steel casing. About 15 pounds of the uranium reacted completely before the device blew apart. With just 15 pounds of matter converted into raw energy, the explosion was equivalent to 30,000 pounds of TNT. 70,000 people were killed almost instantly, their clothes burned to their skin, and for some even their internal organs sucked out of their throat. For decades the United States suppressed grisly footage taken in the days after the bombing, and whithheld key details about the extent of what had been done to the people of Japan. Of course that single event meant that for many years afterwards the rate of cancer was alarming, and many children were born with serious physical defects.
Although a purely uranium device is devastating enough, much of the research done in the Manhattan Project was to overcome the physical limitations of making a more powerful device using plutonium. After much research with timed detonators and high explosives, a configuration with a 13 pound hollow ball of plutonium was expected to cause the same kind of outrageous explosion. An inner core of plutonium and aluminum was surrounded by 32 wedges of hexagonal and pentagonal high explosives laid out in exactly the same pattern as a standard soccer ball. Due to the complexity of the device nicknamed “Gadget”, a test was prepared to make sure it would function according to design. In the early morning on July 16th, 1945 it was tested in the sparse desert of New Mexico. Although two of the detonators were miswired, the other 30 pieces were still timed closely enough to cause the inner core to go to a prompt-critical state, creating an explosion much larger than anyone had expected.
The exact same configuration of high explosives and plutonium were used in the Fat Man device which was dropped 61 years ago today over Nagasaki. To mark this event, a year ago a group of Japanese monks walked hundreds of miles from San Francisco in order to arrive at the test site on the 60th anniversary of the bombing. Although I didn't walk the entire distance, I was with that group that day at the White Sands missile range, and I must say that the experience was exhilirating. Gathered at the Trinity test site at the exact spot where Gadget was tested, they offered prayers of hope that the world will never see the use of a nuclear weapon again. We all looked on in agreement, certainly having the same hope.
I feel it is important that we become informed, and educate our children about the outrageous outcome of nuclear weapons. I am glad the plans were recently scrapped to adapt the W-88 nuclear device to become a powerful “nuclear bunker buster”. I have concern for the strange explosion with a mushroom cloud which occurred in North Korea two years ago on that country's 56th birthday. I hope that the smaller kiloton-yield “suitcase” devices left over from the Soviet stockpile remain out of the hands of rogue states.
Overall I have a hope that people all around the world will be successful in bringing peace during these tumultuous times. We can each make a difference in our homes, schools, and with those we know.