Where are we going with this? This page will assist in developing the ability to compare and contrast nuclear reactions with chemical reactions and to describe nuclear changes in matter, including fission, fusion, transmutations, and decays.
Types of Nuclear Reactions
Reactions in the nucleus can take numerous forms. We should define them!
But first… A term you might encounter that you need to recognize! Nuclear reactions produce a transmutation of the element or elements involved. Transmutation is the conversion of one element into a different element as a result of changes to the number of protons in the nucleus. Transmutations can occur either spontaneously or they can be induced.
What causes nuclear reactions?
So, one example would be if you kept jamming more and more protons into the nucleus. The nuclear attractive forces keep trying to hold them together but the repulsive electromagnetic forces keep "pushing against" the nuclear force. Now, think of the nuclear force as a spring. Which eventually snaps! BLAM! The whole thing flies apart all at once!
The attractive nuclear force, called strong nuclear, operates only at very, very small distances. The repulsive electromagnetic force operates at much, much larger distances. Thus, the bigger the nucleus, the less affect the strong nuclear force can produce. At some point the strong nuclear "spring breaks" and everything goes flying!
There are many nuances to this! But, at the most basic level, nuclear reactions occur because of instability in the nucleus of an atom caused when the repulsive electromagnetic forces becomes greater than the attractive strong nuclear forces.
It's important to note that not all changes to the nucleus result in an unstable atom. Remember isotopes? So, for instance, you can jam a neutron into hydrogen and get a stable isotope. But if you keep jamming them in, eventually it becomes unstable.
Types of Nuclear Reactions
Fission is the splitting of the nucleus of a very heavy element into two—sometimes three—smaller nuclei. Fission can occur spontaneously, but that is, according to some paradigms, not considered a nuclear reaction. Fission can be induced by adding additional particles (usually neutrons) until the element becomes "overloaded" and unstable.
By adding neutrons, the size of the nucleus increases until, at some point, the distance between particles is greater than that which strong nuclear forces can be effective resulting in the splitting of the nucleus.
Fission reactions produce energy.
Fusion is the combining of two or more atoms of small element into one or more different atoms.
For example, two hydrogen isotopes, H-2 and H-3 (sometimes called "heavy hydrogen"), can be jammed together to produce helium, energy, and a neutron.
Fusion is the process that happens within the sun. Fusion requires a great deal of energy to initiate, but once it begins, it produces even more energy. Hence… the sun… and stars…
Alpha Decay is the emitting of alpha particles from the nucleus of an atom causing the original atom to decay or transform into a different atom—an atom with a mass 4 less than the original and an atomic number 2 less.
Alpha decay occurs spontaneously in some elements. It can also result from induced reactions.
Noteworthy is the practice of ignoring the electrons in nuclear reactions. The alpha particle is identical to a helium atom without electrons. That's to say it has an ionic charge of -2. The atom left behind ends up with two extra electrons! So… what happens.
Once more, in this introduction, we'll stick to the shallow end of the pool. Since most considerations of nuclear chemistry do not deal with the electrons, we'll be okay!
Summing up a lot of sources, the left-behind electrons will eventually stabilize; they find some place to go. For instance, in metals, they can join the conduction band. As for the emitted particle, it can pick up electrons from the environment and become a stabilized helium atom.
So, on a universal scale, the electrons all find a home, eventually.
It is further noteworthy to consider what happens when the alpha particle contacts… say a person… before becoming stable. The charged, heavy, fast moving alpha particle will try to stabilize as fast as it can. If ingested, inhalied, or injected into living cells, there is an increased chance of breaking the double-strands of the DNA. This leads to numerous medical considerations and applications. Source
In beta decay, a ß- beta particle is emitted from a neutron, converting the neutron to a proton and increasing the atomic number of the element by 1. However, the atomic mass of the element stays the same.
Positron Emission is the emission of a positron from the nucleus of an atom. It occurs when there are not enough neutron (relative to the number of protons) to keep the nucleus stable.
In positron emission, a proton emits the ß+ positron, converting it into a neutron. This decreases the atomic number by 1, but does not change the atomic mass.
Electron Capture is the process by which, in a neutron-poor atom, an electron reacts with a proton to produce a neutron. This occurs in order to stabilize the atom's nucleus.
The conversion of the proton to a neutron does not change the atomic mass, but it does decrease the atomic number by 1.
Electron capture additionally results in the emission of x-ray radiation.
Gamma Ray Emission is emission of high-energy electromagnetic radiation in the form of γ rays (gamma rays) from the nucleus of an atom.
Gamma ray emission are energy, so they do not affect either the mass number or atomic number of element(s) involved in the reaction.
Spallation occurs when a nucleus is hit with enough energy to cause some neutrons and/or protons to be broken free and emitted.