Los Alamos-The Cradle Of Atom Bombs
By Nicole Tolmachev
With the Second World War came a new type of weapon – one of the most dangerous the world had ever seen: the nuclear weapon. The research and production of the first ones ever to be made were led by the USA and supported by the UK and Canada. The Manhattan Project flourished under the leadership of Major General Leslie Groves from the U.S military and Robert Oppenheimer a theorist and physicist. Although they were an unlikely duo, they were a powerful one.
Between the years 1942 and 1945, during World War 2, a research city rapidly developed in the desert of New Mexico. It was called Los Alamos and its real address was kept secret from the outside world. The official one where all the belongings of the researchers and letters to them arrived is quite famous today: P.O. Box 1663, Santa Fe, New Mexico.
As a result, two types of atom bombs were developed. Their names were Little Boy and Fat Man.
The Discovery of Nuclear Fission
Atom bombs could only be developed because several years prior to the Manhattan Project three scientists discovered the fission of nuclei. The two German chemists Otto Hahn and Fritz Strassmann agreed to do an experiment with the Jewish physicist Lise Meitner. Sadly for Meitner, she had to flee from Germany before they could conduct it. It’s said that Hahn even gave her a diamond so she could bribe the guards at the border if they wouldn’t let her out. She successfully fled to Sweden in 1938.
On December 17th, 1938 the two chemists conducted the experiment and found something unbelievable. After shooting neutrons at uranium and other elements, two different ones emerged out of them. Hahn and Strassmann weren’t able to explain the discovery as chemists. They send the results of the experiment to Lise Meitner who found an explanation with her nephew Otto Robert Frisch: After getting shot by a neutron the nucleus of co-called heavy elements splits into two and new elements emerge. They had discovered nuclear fission.
These new nuclei are less massive than the original one. That’s because after getting hit by a slowed-down neutron the nucleus releases some of its own neutrons and a great amount of energy. These now free neutrons can cause a nuclear chain reaction if they hit other nuclei. They would release energy and neutrons as well. These neutrons would hit other nuclei in that element and induce fission there. Theoretically, this chain reaction could go on infinitely.
The amount of released energy is so big because of the great difference in mass between the original nucleus and the neutron it absorbs and the new nuclei and the neutrons they release. This enormous energy released by nuclear fission is what’s important when building an atom bomb.
The Project
The USA participated in the war because of an attack on their fleet by the Japanese. The Manhattan Project itself was created to have a defence against Nazi Germany, who was working on their own nuclear weapons. The first facility built for this project was in New York. In just three years the Manhattan Project saw incredible growth and rapidly became one the most expensive projects of its kind.
Originally the military planned to have very strict secrecy. They wanted the scientists to only know of what was happening at their own desk. What was going on the table right next to them should have been top secret, much like in “the Ministry of Truth” in Orwell’s dystopia “1984”.
This plan was met by massive protests of the scientists and many of them left. They said that like this they wouldn’t be able to get anywhere with the project. A task as difficult as creating the first nuclear weapons required a lot of communication to complete successfully. Luckily the scientific head of the Manhattan Project agreed to that. With Oppenheimer’s help, the secrecy wasn’t as strict as planned and many researchers returned to Los Alamos.
The Trinity Test
At 5.30 am on the 16th of July 1945 the results of three years of intense work had their time to shine. At a Bombing and Gunnery range far away from the research site and any town the developed bombs were tested. The Fat Man bomb had its first successful detonation there for example. It had a strength of 21.000 tons of TNT.
If you are interested in seeing what an explosion of that power looks like you can click this link: https://www.youtube.com/watch?v=7dfK9G7UDok. It’s a video showing the original footage from the Trinity test.
From Fission to Explosion
In this article, we already established that nuclear fission causes a nuclear chain reaction that releases energy. How can this be made into a devastating explosion?
To put it simply: The fission process is faster than a blink of an eye and if you miss that short time window to assemble your bomb pre-detonation will happen. Pre-detonation means that the neutron passes through your fissionable element without inducing fission. That means no energy release, no chain reaction, and no explosion.
This happens with nuclei that have a so-called critical mass; essentially, they are really heavy and are fissionable. To make the best out of the situation you have to combine two of them to get a supercritical mass. If that combination takes place at the right time and no pre-detonation happens, you get a nuclear explosion.
Both the Little Boy and Fat Man bomb worked like that, although the creation of the supercritical mass was executed differently.
The Little Boy used Uranium-235 as fissionable material. The chain reaction that happens in it can be controlled pretty easily which gives a generous time window of a thousandth of a second to work with. As a result, it was relatively uncomplicated to get an explosion with that bomb. The downside was, that Uranium-235 is really rare. Getting it was difficult and costly because it had to be extracted from regular uranium.
Uranium-235, just like Uranium-238 for example, is an isotope of uranium. Isotopes are variants of a certain element. Although they have the same ordinal number in the periodic system and the same chemical properties, their masses and physical properties are different from each other.
For the Fat Man, another element was being used: plutonium. Plutonium was recently discovered back then. It was a by-product in nuclear reactors, which were also a new thing in the 1940s. That means plutonium is way easier and cheaper to produce than Uranium-235. But there’s a reason why the Trinity Test was the first successful detonation of the plutonium bomb.
Plutonium has a high chance of spontaneous fission, which is fission that can start on its own at any given moment, without the need to induce it with neutrons. Due to this, the probability of pre-detonation is way higher than with Uranium-235 and the time window is way shorter. To solve this problem the researchers developed a new assembly method for the Fat Man.
Implosion was used to create the supercritical mass. Implosion is the opposite of an explosion. Everyone has seen an explosion before; a huge amount of energy is directed outward, away from its source. These energies are the shockwaves and the fire we can see and feel. When something implodes, all this energy is directed inward, toward itself. Using this the plutonium bomb could be assembled without any pre-detonation, as high explosives were being used.
The Aftermath
Shortly after the success of the Trinity Test, the Little Boy and Fat Man bombs were used by the U.S to force Japan to surrender. The bombings of Hiroshima on August 6th, 1945 and Nagasaki on August 9th, 1945 are infamous as they flattened out both cities. For the prior, the uranium bomb was used and for the latter the plutonium bomb. These attacks forced Japan to officially surrender on the 14th of August 1945.
The Manhattan Project is also correlated with the creation of the hydrogen bomb. Edward Teller, its inventor, had his own little research team at Los Alamos working on the first research for the H-bomb. Though it didn’t bring a lot of fruition during the Manhattan Project, the research conducted there was the stepping stone to its creation.
The Conclusion
The atom bombs all in all brought a lot of death and suffering to the world, as other countries also developed their own nuclear weapons. The three scientists that first discovered nuclear fission wanted their discovery to bring good to the world and though the military has disappointed them, medicine and technology haven’t.
The conclusion of the Manhattan Project started the atomic age in which nuclear fission was the number one energy source of the world. Fission was also highly used in medicine at that time(i.e. to sterilise equipment or to examine thyroid glands to determine whether they are still healthy). The use of nuclear energy was observed and controlled by the Atomic Energy Commission.
The discovery of nuclear fission set a lot of events in action, both good and bad. As with almost everything in this world it is our own decision which side to prioritise.