What is Beta Decay?
Beta decay is the natural radioactive decay within an atom in which beta particles, which include high-energy electrons or positrons – the electron’s antimatter counterpart – are emitted from the atom’s nucleus. This process usually occurs due to instability within an atom and results in the process of transmutation, or the transformation of one element into another, in order to regain stability.
There are two forms of beta decay – beta-plus and beta-minus decay – which determine what beta particles are emitted from the atomic nucleus (which, naturally, contains either a proton or a neutron). In a beta-plus decay process, a proton turns into a neutron, causing the creation of a positron and a neutrino. The beta-minus decay process is the exact opposite; a neutron turns into a proton, causing the creation of an electron and an antineutrino. These changes in the atomic nucleus may cause the loss of a proton or neutron, however, the total amount of nuclear particles, given by the mass number, remains the same. The effect of this change, however, guarantees that the atom’s properties change. Specifically, in the case of a beta-plus decay, the atomic number of a given atom decreases, while, in the case of a beta-minus decay, the atomic number increases.
The concept of neutrinos, subatomic particles, like protons and electrons, that don’t carry any electrical charge and have nearly zero mass, was first discovered due to experimentation of beta decay. When scientists recognized that isotopes were releasing the same amount of energy each time during their decay, but electrons were being detected with different energy levels, they recognized that there had to be another fundamental particle that balanced the Law of Conservation of Energy, leading to the neutrino.
Beta decay is one of three kinds of radioactive decay – the others being alpha and gamma decay. All three of these kinds of decay are due to the instability of the atomic nucleus, but the kinds of radiation emitted are completely different. In alpha decay, alpha particles are emitted, which is composed of two neutrons and two protons, which, in simple terms, is the element helium. Gamma decay, on the other hand, is the result of both alpha and beta decay, since the atomic nucleus contains extra energy after going through such a transformative change. That excess energy is released in the form of gamma rays, a high-energy form of electromagnetic radiation.
Antimatter is a key concept when discussing the radioactive decay, but especially important for beta decay. Antimatter contains all of the properties of ordinary matter with opposite charge. Consequently, the model of an atom containing antimatter has an antineutron and antiproton nucleus that is orbited by the “antielectron”, or positron. Neutrinos, subatomic particles, like protons and electrons, that don’t carry any electrical charge and have nearly zero mass, also have an antimatter counterpart in antineutrinos.
When matter collides with antimatter, both types of matter are annihilated, and their mass is converted into pure energy. It was from this relationship that the famous mass-energy equivalence equation, E = mc2, was developed.
Beta Decay Equation
Each of the subtypes of beta decay – beta-plus and beta-minus decay – have clear equations. However, it is important to note that these equations say nothing about the length of time that it takes for any given unstable nucleus to decay. That is because the reason for that decay is quantum mechanical in nature, making probabilistic models or empirical study our media of choice to determine when decay occurs.
Beta-Plus Decay Equation
The beta-plus decay equation is given as:
where A is the mass number, Z is the atomic number, X is the initial element, X’ is the final element, e+ represents the positron and ve is the neutrino.
The most important part of this equation to note is, of course, the transmutation of the element brought about by the reduction of protons. This is found within the second term of the equation, which displays Z, the atomic number, which represents the amount of protons in an atom, being subtracted by one.
Beta-Minus Decay Equation
The beta-minus decay equation is given as:
which contains many of the same variables that are within the beta-plus decay equation with the exception of e–, which represents the electron, and ve bar, which represents the antineutrino. In this case, the change to the nucleus is the exact opposite of what you see in the beta-plus decay situation. The nucleus receives an additional proton from a decayed neutron, meaning the atomic number goes up by one.
Beta Decay Example
To demonstrate beta decay, let’s use Carbon-14, a well-known radioactive carbon isotope, which is used for carbon dating.
If Carbon-14 were to go through a beta-plus decay, it would look like:
The process of one proton converting into a neutron generates a positron and a neutrino and turns carbon into boron.
If Carbon-14 were to go through a beta-minus decay, it would look like:
The process of one neutron converting into a proton generates an electron and an antineutrino and turns carbon into nitrogen.