Beta-plus decay is a nuclear process in which a proton-rich nucleus reduces its proton count by converting a proton into a neutron, while releasing two particles that carry away charge and energy.

Beta-plus Decay in the Nucleus

When a nucleus has too many protons relative to neutrons, one way it can change is through beta-plus decay. In this process, the change happens inside the nucleus itself, not in the electron cloud outside the nucleus.

That definition gives the essential idea: one nucleon changes type.

Feynman diagram of $\beta^+$ decay at the particle-interaction level: a proton converts to a neutron by emitting a virtual $W^+$ boson, which then produces a positron $e^+$ and an electron neutrino $\nu_e$. This helps connect the “one nucleon changes type” statement to the weak interaction mechanism that creates the emitted leptons. Source

A proton is not simply thrown out of the nucleus. Instead, a proton is converted into a neutron, and two additional particles are emitted at the same time.

Because a proton becomes a neutron, the nucleus ends with one fewer proton and one more neutron.

Textbook-style schematic showing beta-plus decay with a concrete nuclear example and the emitted particles $e^+$ and $\nu_e$. The diagram makes the bookkeeping visible: the nucleus moves to a different element while the mass number stays the same and the atomic number decreases by 1. Source

The total number of nucleons stays the same, so the mass number does not change, but the atomic number decreases by 1.

Nuclear Accounting

• Proton number decreases by 1.

• Neutron number increases by 1.

• Mass number stays the same.

• The daughter nucleus is a different element from the parent nucleus.

The Emitted Particles

The emitted beta-plus particle is called a positron. It is written as $\beta^+$ or $^{0}_{+1}e$ in nuclear equations.

Even though its symbol uses $e$, a positron is not a proton and it is not an orbital electron. It is a distinct particle produced during the decay process. In beta-plus decay, the positron carries positive charge away from the nucleus.

The second emitted particle is a neutrino, written as $\nu_e$. It has no electric charge and interacts only weakly with matter, so it is much harder to detect directly than the positron.

In beta-plus decay, the neutrino leaves the nucleus along with the positron. Including both emitted particles is important when describing the process correctly, because the decay is not complete if either particle is missing from the nuclear equation.

Writing Beta-plus Decay

When you write beta-plus decay symbolically, the parent nucleus appears on the left and the daughter nucleus plus emitted particles appear on the right. The daughter nucleus has the same mass number as the parent but an atomic number lower by 1.

Here, $X$ and $Y$ stand for different nuclei. Since the atomic number changes, the daughter nucleus represents a different element from the parent nucleus.

Reading the Equation

• The left side shows the original nucleus before the decay.

• The right side shows the new nucleus and the emitted particles.

• The same superscript $A$ on both nuclei shows that the total number of nucleons is unchanged.

• The subscript changes from $Z$ to $Z-1$ because one proton has changed into a neutron.

• The positron is written with mass number $0$ because it is not a nucleon.

What Beta-plus Decay Means Physically

Beta-plus decay lets a nucleus reduce its proton count without changing its total number of nucleons. This matters because the identity of an element depends on the number of protons in the nucleus.

After the decay, the daughter nucleus is therefore a different element, even though its mass number is unchanged. The emitted positron carries positive charge away from the decay, while the neutrino is electrically neutral.

The process should be pictured as an internal nuclear transformation. A common mistake is to imagine the nucleus simply ejecting a proton. That is not what beta-plus decay means; the proton is converted into a neutron during the decay.

Another useful way to think about the process is to separate what changes from what does not change. The type of one nucleon changes, the proton count drops, and the neutron count rises. However, the total number of nucleons in the nucleus remains the same throughout the process.

Common Mistakes to Avoid

Several misunderstandings appear often in this topic, especially when reading nuclear equations quickly.

• Do not say a proton is simply expelled from the nucleus.

• Do not forget to include the neutrino in the decay equation.

• Do not lower the mass number of the nucleus.

• Do not confuse a positron with a proton.

• Do not assume the emitted particle comes from the electron cloud outside the nucleus.