Radiotherapy: Nuclear Stability and Radioactive Decay

Flashcards covering the fundamentals of nuclear stability, the n:p ratio, and types of radioactive decay including alpha and beta processes.

Nuclear Stability

The state of a nucleus that depends mainly on the mass number ($A$) and atomic number ($Z$), specifically the ratio of neutrons ($N$) to protons ($Z$).

$n:p$ ratio (Light Atoms)

The stable ratio of neutrons to protons is approximately $1$ for light atoms.

$n:p$ ratio (Heavy Atoms)

For atoms where $Z > 20$, the ratio of neutrons to protons must increase to $1.15-1.5$ to stabilise the nuclides.

Instability Threshold

All nuclides with an atomic number $Z > 83$ are considered unstable.

Radioactive Decay

The process in which an unstable atomic nucleus spontaneously loses energy by emitting ionising particles and radiation, resulting in a change within the nucleons.

Neutron-rich nuclides

Nuclides that undergo $-1\text{beta}$ decay, which converts a neutron into a proton to shift the ratio toward the band of stability.

Proton-rich nuclides

Nuclides that undergo positron decay ($+1\text{beta}$) or electron capture to convert a proton to a neutron.

Parent nuclide

The original atom of one type before it undergoes radioactive decay and transforms into a different type.

Daughter nuclide

The atom of a different type that results from the transformation of a parent nuclide during decay.

Alpha decay

A decay mode for very heavy nuclides that reduces both $N$ and $Z$ by allowing $2$ protons and $2$ neutrons to escape the nucleus.

Alpha particle

A particle identical to helium-4, containing $2$ protons and $2$ neutrons without electrons, carrying a charge of $+2e$.