Transmutation

Transmutation Definition

Let's start by looking at the definition of transmutation.

Basically, "transmutation" is when one element becomes another through some form of nuclear process.

Causes of Transmutation

There are two main types of transmutation:

1. Nuclear reactions

2. Radioactive decay

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)

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.

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.

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.

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

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.