For centuries, alchemists had been striving to reach their ultimate goal: creating gold. They called that process chrysopoeia. They aimed to make a Philosopher's Stone that could transform base elements into gold.
Unfortunately for the alchemists, making pure gold through chemical elements is not possible. However, gold can be made through transmutation.
In this article, we will learn about the process of transmutation: what it is, how it occurs, and some examples. Keep reading to find out how chemists have finally solved this ancient problem!
- This article covers the topic of transmutation
- First, we will define what transmutation is
- Next, we will learn the causes of transmutation
- After that, we will look at how transmutation can occur both naturally and artificially
- Lastly, we will learn about a special type of transmutation called nuclear fission
Transmutation Definition
Let's start by looking at the definition of transmutation.
Transmutation is the process of a nucleus gaining/losing protons to become a new element with a different atomic number
Basically, "transmutation" is when one element becomes another through some form of nuclear process.
Frederick Soddy and Ernest Rutherford had the first true observation of transmutation in 1901 when they watched thorium converting into radium through radioactive decay.
Soddy then cried, "Rutherford, this is transmutation!".
Rutherford replied: 'Soddy, don't call it transmutation, they'll kill us for being alchemists!'
Causes of Transmutation
There are two main types of transmutation:
Nuclear reactions
Radioactive decay
Nuclear reactions are when two nuclei (or a nucleus and another subatomic particle) collide to form one or more new nuclei
Radioactive decay is the process of an unstable nucleus stabilizing itself through radiation
There are two main "causes" of transmutation: natural and artificial. Let's break these down, shall we?
Natural Transmutation
Let's focus on natural transmutation first.
Radioactive decay
Radioactive decay occurs naturally when a nucleus gets too unstable. To stabilize itself, it emits radiation in the form of particles, such as neutrons or alpha particles (helium nucleus)
Radioactive decay doesn't always transform an element into a new species. For example, carbon-14 can emit (lose) neutrons to form carbon-12
For example, here is the process of radium-226 emitting an alpha particle to become radon-222:
Fig.1-Radioactive decay of radium-226
The number on the top-left is the atomic mass, which is equal to the number of protons + neutrons. The number of the bottom-left is the atomic number, which is equal to the number of protons. Every element has a unique atomic number, so a change in protons results in a change of element.
In this case, radium is losing two protons when it emits the alpha particle, which causes it to become radon.
Nuclear reactions
The main natural nuclear reaction is stellar nucleosynthesis.
Stellar nucleosynthesis is the creation of new elements within stars by the process of nuclear fusion
Nuclear fusion is the process of two or more nuclei combining to form one or more new nuclei and subatomic particles
Smaller stars can create elements like helium and lithium, while heavier stars can fuse heavier elements like iron. Elements heavier than iron, such as gold, can be formed through natural transmutations in supernovas (explosions of stars).One of the more famous examples of stellar nucleosynthesis is solar fusion, which is the nuclear fusion process that occurs in our sun.
Fig.2-The process of solar fusion
Basically, different hydrogen nuclei smacked into each other until they had enough protons and neutrons to form a stable helium atom.
Did you know that the process of solar fusion produces 3.8x1026 joules of energy per second? That's enough energy to power 6.3x1024 60-watt lightbulbs per second or power one 60-watt lightbulb for 2x1014 millennia. That's a lot of energy!
Artificial Transmutation
Now let's talk about artificial transmutation.
When particles from a linear accelerator, cyclotron, or synchrotron hit atoms of one element, the atom changes in some way. This is called "artificial" or "induced" transmutation. All the elements with atomic numbers higher than 92, like plutonium, are made by humans through a process called transmutation. Most nuclear reactions involve the artificial transmutation of elements, but they are usually called "fission," "fusion," or "irradiation" instead of "transmutation."
Fig.3-A linear accelerator
Using particle accelerators that bombard elements with alpha particles, deuterons, or small nuclei, it is possible to change one element into another. Some protons from the bombarding particles get stuck in the nucleus of the target element, which speeds up the change. In a nuclear reactor, neutrons hit the target nucleus, which makes the nuclei split apart.
In early tests, a nucleus was hit with alpha particles from bismuth-214 (214Bi) that were moving very quickly. Rutherford did the first nuclear reaction with these alpha particles and nitrogen in 1919. In this reaction, a fast-moving helium nucleus reacted with a slow-moving nitrogen nucleus to make two new nuclei and a proton. This showed that elements can change into other things.
Rutherford, a physicist, got the Nobel Prize in chemistry in 1908 for essentially doing alchemy. Alchemy didn't turn lead into gold, as many alchemists had hoped for centuries, but it did let some elements change into other elements!
Examples of Artificial Transmutation
Here are some examples of artificial transmutation:
1-By smashing an alpha particle into the nucleus of nitrogen, you can turn it into oxygen. As part of the change, a single atom of hydrogen is made.
$$^{14}_7Ne + ^4_2He \rightarrow ^{17}_8O + ^1_1H$$
2-Adding an alpha particle to the nucleus of aluminum changes it into phosphorous. As a result of the change, a neutron is made.
$$^{27}_{13}Al + ^4_2He \rightarrow ^{30}_{15}P + ^1_0n$$
It's important to remember that the three "conservation laws" apply to nuclear reactions:
- The charge stays the same, which means that the total of the charges on the left is the same as the total of the charges on the right.
- In a nuclear reaction, there is no change in the number of nucleons.
- The relationship between mass and energy is stable.
Nuclear Fission
We talked earlier about nuclear fusion, but there is also the "opposite" reaction called nuclear fission
Nuclear fission is the process of a heavy nucleus splitting, either spontaneously or during impact with another particle
For example, below is the splitting of uranium due to a collision with a neutron:
Fig.4-Nuclear fission of uranium
When a neutron crashes into a bigger atom, it causes the bigger atom to get excited and split into two smaller atoms. These smaller atoms are called fission products. Neutrons are also given off, which can set off a chain reaction. When each atom breaks apart, it gives off a huge amount of energy.
Uranium and plutonium are used most often in nuclear power reactors for fission reactions because they are easy to start and keep under control. In these reactors, fission gives off energy that heats water to make steam. The steam turns a turbine to make electricity that doesn't have any carbon in it.
Transmutation - Key takeaways
- Transmutation is the process of a nucleus gaining/losing protons to become a new element with a different atomic number.
- Nuclear reactions are when two nuclei (or a nucleus and another subatomic particle) collide to form one or more new nuclei
- Radioactive decay is the process of an unstable nucleus stabilizing itself through radiation
- Stellar nucleosynthesis is the creation of new elements within stars by the process of nuclear fusion
- Nuclear fusion is the process of two or more nuclei combining to form one or more new nuclei and subatomic particles
- Nuclear fission is the process of a heavy nuclei splitting, either spontaneously or during impact with another particle
References
- Fig.1-Radioactive decay of radium-226 (https://upload.wikimedia.org/wikipedia/commons/thumb/2/21/Alpha-decay-example.svg/640px-Alpha-decay-example.svg.png) by MikeRun on Wikimedia Commons licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/)
- Fig.2-The process of solar fusion (https://upload.wikimedia.org/wikipedia/commons/thumb/7/78/FusionintheSun.svg/640px-FusionintheSun.svg.png) by Borb (https://commons.wikimedia.org/wiki/User:Borb) licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/)
- Fig.4-Nucleur fission of uranium (https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Nuclear_fission_reaction.svg/640px-Nuclear_fission_reaction.svg.png) by MikeRun on Wikimedia Commons licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/)
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