Nuclear decay

Nuclear decay or radioactive decay is the random process by which an unstable atomic nucleus loses energy through emission of radiation in order to become more stable. A nucleus decays into one or more nuclear nuclei or particles, called decay products, with fewer resulting particles being more common. The property of decaying is often called radioactivity. Conventionally, when a nucleus decays into another nucleus, they are called the mother nucleus (or parent nucleus) and daughter nucleus respectively.

For decay to occur at rest (that it, without external influence), it must be energetically favorable. For this to be possible, the total mass must decrease, which implies an increase in binding energy (across all decay products) and therefore greater stability. In the case of a two-body decay involving loss of nucleons, we can write

where $A,Z$ are the mass number and atomic number of the original atom and $A'$ and $Z'$ are the number of nucleons/protons that got ejected by the decay.

Mode#

There are three main modes of decay exist:

• Alpha decay, which leads to the emission of a helium nucleus (called an $\alpha$ particle);
• Beta decay, which converts a proton into a neutron or vice versa;
• Gamma decay, which leads to the emission of a high-energy Photon.

Another mode, somewhat different, is spontaneous fission, occurring only for very heavy nuclei ($A\gtrsim230$), where the nucleus splits into two smaller nuclei instead of emitting single particles.

Mechanism#

The exact mechanism depends on the type decay of decay. It is nonetheless possible to create a high-level macroscopic theory that describes the loss of mass and nuclei in an unstable object due to decay irrespective of type. This common treatment is available via the radioactive decay law.