In the experiment that was performed that initially split the atom, the explanation goes that you take a neutron and fire it into a heavy, unstable element like U-238 which splits into more neutrons and releases some energy etc etc etc.
We’ve all heard it.
However it seems to miss the part around how you obtain the initial neutrons. As far as I’m aware they don’t occur naturally on their own, so how did they obtain enough of them to split the atom in the experiment?
(I’m aware that for the bomb they combine too lumps of U238 to create a super critical mass, however I’m more interested in the initial experiment)
In: 72
First off neutrons definitely do occur naturally. Cosmic rays can create free neutrons and so can radioactive elements. This is actually a huge concern for nuclear weapons design because the wrong isotopes (such as Pu-240) create too many spontaneous neutrons and can start the reaction too soon. However, neutrons can be created numerous ways. Mixing certain radioactive elements can create them, so can a linear accelerator, neutron spallation device or a fusion reactions. These are all used in weapons design and testing.
There’s a variety of ways, one method is using beryllium and an alpha emitter such as radium, once the alpha particle from the radium interacts with the beryllium it then releases a free neutron (a neutron not inside an atom)
“Irradiation of beryllium with alpha particles results in complex nuclei formed by absorption of the alpha particles by 9Be nuclei. These complex nuclei are highly excited and a neutron is emitted almost instantaneously (within approximately one billionth of a second).”
[Article if your interested ](https://www.sciencedirect.com/topics/earth-and-planetary-sciences/neutron-source#:~:text=Irradiation%20of%20beryllium%20with%20alpha,one%20billionth%20of%20a%20second).)
Radioactive decay can release neutrons, particularly when alpha particles hit any of several light isotopes including isotopes of beryllium, carbon, or oxygen.
When detonated, the bomb design makes sure there is a “super critical” mass of uranium or plutonium. This means getting the “fuel” together, compact enough, so that if a few neutrons gets things going, you would have an atomic explosion.
There is a chance that a random decay of the uranium (or plutonium) could liberate a neutron, or there could be a stray comic ray, but bomb makes don’t like to take chances. So they make sure there are plenty of neutrons at the exact right moment.
What the original bomb makers did was put an “initiator” at the center of the where the super critical mass will be (center of plutonium implosion), or where gun will fire uranium piece at target.
The initiator is a beryllium pellet, with a beryllium shell and polonium between the two. They do NOT touch, there is a tiny gap between the polonium and beryllium. Polonium is radioactive and continuously makes a lot of alpha particles (really high speed helium atoms). When the alpha particles hit the beryllium, they knock neutrons out that will start the reaction. Having a tiny gap, normally no neutrons are being made.
The initiator is set up so that when the bomb is detonated and the “fuel” (uranium or plutonium) are smashed, that crushes the initiator and mixes the beryllium and polonium to generate a lot of neutrons.
Today, this is done with a tiny particle accelerator tube (there are several types).
**tl;dr there are ways to geneate neutrons, on demand, at the exact right moment when the uranium or plutonium is super critical.**
Back in the day, scientists used a mixture of beryllium sulfate and radium sulfate. Radium is an alpha radiation emitter, and Beryllium releases neutrons when shot with alpha particles. The sulfates are used because they are powders and mix better than the pure metals.
This is actually the method James Chadwick used when he discovered the neutron.
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Alright, kiddo! 😊
Step by step:
1. Everything is made of tiny things called atoms.
2. Inside these atoms, there are even tinier parts. One of these parts is called a neutron.
3. Scientists have big machines called particle accelerators.
4. In these machines, they speed up atoms super-fast and smash them together.
5. When the atoms crash, the tiny parts, like neutrons, come out.
6. Scientists then study these neutrons.
So, we get a neutron by using big machines to break apart atoms! Cool, right?
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