# Nuclear Reactions

## Key Questions

• A nuclear reaction involves changes to the nucleus of an atom. Reactions can be spontaneous or can result from the interaction with other particles.

A spontaneous nuclear reaction may result in the release of a neutron or proton from the nucleus. Sometimes the nucleus can release several of these at once. Sometimes they can split into two nuclei. An "alpha particle" is the result of the release of two protons and two neutrons together. You should recognize that this configuration forms the nucleus of a Helium atom.

If a nucleus collides with another particle, there can also be a reaction. Neutrons can cause reactions. Such an interaction could simply result in the Neutron being absorbed. This creates a new isotope of the element. Neutron absorption can make a nucleus unstable and more likely to split into several parts.

Chemical reactions , on the other hand, do not change the nucleus of the atoms. These reactions involve only the bonds between atoms and the clouds of electrons which surround the nucleus.

If you set fire to a piece of paper, oxygen from the air is combining with carbon and hydrogen in the paper to form carbon dioxide, carbon monoxide, water, and a few other compounds. If you could capture all of the smoke and measure all of the paper and oxygen consumed in the process, you would find that you start with the same atoms you end up with.

A chemical reaction which begins with a certain amount of carbon, nitrogen, and zinc will have those same elements in the same quantities at the end of the reaction. A nuclear reaction may start with a certain quantity of plutonium and end with some amount plutonium, uranium, lead, and iron (and probably lots of other things).

• A nuclear reaction is a reaction that changes the mass of the nucleus. Nuclear reactions occur both in nature and in nuclear reactors. In nuclear reactors the standard nuclear reaction is the decay of uranium-235.

The superheavy elements in the periodic table, that is to say, those with atomic numbers exceeding 83, undergo alpha decay to reduce the number of protons and neutrons in the nucleus of the atom.

Elements with a high neutron to proton ratio undergo beta decay, in which a neutron is changed into a proton and an electron. As the entire process takes place in the nucleus of the atom, and the nucleus can only contain protons and neutrons, the electron that is generated is ejected from the nucleus as a beta particle.

Gamma decay, unlike the other modes of radioactive decay, does not change the number of protons and neutrons in the nucleus of the atom- instead, it lowers the atom's energy level by one.

An example of alpha decay would be the decay of uranium-235 into thorium-231:

""_92^235 U + ""_90^231 Th $\rightarrow$ $\alpha$

An example of beta decay would be the decay of uranium-235 into neptunium-235:

""_92^235 U + ""_93^235 Np $\rightarrow$ $\beta$

An example of the gamma decay of technetium-99m into technetium-99:

""_43^(99m) Tc + ""_43^99 Tc $\rightarrow$ $\gamma$

The 'm' in Tc-99m stands for metastable, which in terms of an atom, ion or atomic nucleus, means that the atom is in an excited state.