.png)
As of today, July 30th 2023 the world is still hyped about Oppenheimer by Christopher Nolan, in which Doctor Oppenheimer along with their team build the atomic bomb, forever changing the history and ethicality of wars. In according to release of the movie this month, google searches such as “Nuclear bomb” have risen much higher than their regular plank:
In light of such an uprising of nuclear physics, it’s most appropriate to talk about nuclear fission and the chain reaction of Uranium-235 that has been used in nuclear power plants and first prototypes of atomic bombs. Let’s delve into some mind blowing physics!
First of all, what is nuclear fission? You might’ve heard of radioactive decay, in which a certain substance decays on its own, turning a nuclei of one atom into another with additional byproducts. A very well-known radioactive decay reaction is alpha decay. In that reaction, an atom spontaneously splits into a helium atom and a daughter nuclei, which loses two protons and two neutrons.
Image credit: Sciencedrill.com
How’s uranium-235 fission different from this radioactive decay? In the latter, the nucleus is so unstable that it breaks apart spontaneously, and in the former, we have to drive the reaction to commence. In the case of Uranium-235, a fast neutron needs to hit the nucleus of U-235 in order to split the atom into two parts, Barium and Krypton. The specific catch about Uranium-235 is that after the nucleus is thus split, it throws out more neutrons that can initiate another chain reaction if it hits another nucleus.
As you can feel, if each division can provide us with energy (up to 200 MeV each) this procedure can quickly become a chain reaction, which would release monstrous amounts of energy.
The catch here is the probability of a neutron hitting a nucleus - a neutron can pass by many nuclei before hitting one, and the mathematical calculations turn to probability. The chances can obviously be manipulated in our favor, though it still feels like a guessing game to an extent. This is why on the Trinity test of the atomic bomb, scientists have feared that there is a chance that the chain reaction might be stronger than estimated, since nobody (besides Russians) at that time has done nuclear testing at that scale. At one point, the team also believed that there is a possibility of igniting the atmosphere from such heat, due to fission of nitrogen, but that has only been observed to happen at the cores of massive late-stage stars. The odds were roughly one in three million, but it was nonetheless scary for humanity to bet their existence on an unexplored path of uncertain probabilities without having almost no prior experimentation. Although now we know that the ignition of the atmosphere from that bomb is impossible, using such a weapon felt like a gamble at that time.
A frame from the Oppenheimer movie teaser.
Fortunately, not all uranium makes a large nuclear explosion upon encountering a neutron. About 99% of all uranium on earth is uranium-238, which does not undergo such a fission reaction, and only the remaining 1% is natural uranium-235. Though uranium can be enriched in order to be suitable for a bomb, we need not worry that all radioactive metal in the earth’s crust will spontaneously combust.
Luckily, not all fission reactions that occur in uranium are chained reactions - the fission used in nuclear power plants is controlled and does not go out of hand. Scientists calculate the neutron multiplication factor, k, in order to control the rate of fission reaction. If k is less than one, the chain reaction is subcritical, and the neutron population will decay. If the k value is bigger than one, then a chain reaction can occur that would lead to an explosion. Nuclear power plants monitor the neutron multiplication factor around one in order to maintain stable energy production.
The energy from fission reactions is monstrous, and this energy can either be carefully controlled for massive energy production for daily use, or all this energy can be at once deployed in order to cause unbelievable destruction. This is why the development of such technologies is also a question of morality, which is what the Oppenheimer movie greatly showcases. This movie is an exciting watch, and perhaps you now know a little more about the context of the movie, which can help you understand the central dilemmas that the characters had in the movie by developing such a destructive weapon.
Links & Resources:
https://nrl.mit.edu/reactor/fission-process - More on the Fission Process
https://www.quora.com/What-stops-the-chain-reaction-during-a-nuclear-explosion - How does the reaction stop?
https://www.syfy.com/syfy-wire/could-oppenheimer-atomic-bomb-really-have-destroyed-the-world#:~:text=In%20every%20case%2C%20explosions%20released,to%20block%20out%20the%20Sun.&text=In%20that%20case%2C%20temperatures%20would,plants%20and%20animals%20would%20diminish. - was total destruction of the world really possible?
Commenti