The most common type of radioactive decay occurring naturally within the human body is beta-minus decay. This process is primarily driven by the presence of two naturally occurring radioactive isotopes: Carbon-14 ($^{14}C$) and Potassium-40 ($^{40}K$).
These isotopes are fundamental components of our bodies. Chemically, they behave identically to their stable counterparts, stable carbon and stable potassium, integrating into all cells and tissues.
Understanding Beta-Minus Decay
Beta-minus decay ($\beta^-$ decay) is a type of radioactive decay in which a neutron in an unstable atomic nucleus is transformed into a proton. During this transformation, the nucleus emits an electron (known as a beta particle) and an antineutrino. This process increases the atomic number by one, but the mass number remains unchanged, effectively transforming the element into a new one.
For example, when an atom undergoes beta-minus decay:
- Neutron $\rightarrow$ Proton + Electron ($e^-$) + Antineutrino ($\bar{\nu}_e$)
This decay mode is prevalent because it allows neutron-rich isotopes to achieve a more stable configuration by converting excess neutrons into protons.
Key Radioactive Isotopes in the Human Body
Our bodies naturally contain several radioactive isotopes, but Carbon-14 and Potassium-40 are the most significant contributors to internal radiation exposure due to their abundance and decay characteristics.
| Isotope | Primary Decay Mode | Product Nucleus | Contribution |
|---|---|---|---|
| Carbon-14 ($^{14}C$) | Beta-minus ($\beta^-$) | Nitrogen-14 ($^{14}N$) | Forms naturally in the atmosphere and is incorporated into all organic matter, including human tissues. |
| Potassium-40 ($^{40}K$) | Beta-minus ($\beta^-$) | Calcium-40 ($^{40}Ca$) | An essential electrolyte, potassium is abundant in the body. Approximately 89% of $^{40}K$ decays via beta-minus. |
| Potassium-40 ($^{40}K$) | Electron Capture (EC) | Argon-40 ($^{40}Ar$) | Approximately 11% of $^{40}K$ decays via electron capture, also producing gamma rays. |
Why Beta-Minus is Most Common
Both Carbon-14 and Potassium-40 are among the most common natural radioactive isotopes in humans. While Potassium-40 also undergoes electron capture, its predominant decay mode, representing approximately 89% of its decays, is beta-minus. Carbon-14 exclusively undergoes beta-minus decay.
Given that both these significant isotopes primarily or exclusively decay via beta-minus emission, this makes beta-minus decay the most frequent type of nuclear transformation occurring within the human body. The continuous decay of these isotopes contributes to the natural background radiation dose we receive daily.
