Alpha Decay
What is Alpha Decay?
Alpha decay is a type of radioactive decay in which a parent nucleus \( P \) decays into a more stable daughter nucleus \( D \) by emitting an energetic alpha particle \( \alpha \). An alpha particle is a \( ^4_2He \) nucleus, consisting of two protons and two neutrons.
In alpha decay, the parent nucleus loses two protons and four nucleons, resulting in the atomic number \( Z \) of the parent decreasing by 2 and its mass number \( A \) decreasing by 4.
General Formula for Alpha Decay:
The general equation for alpha decay is:
\( P \rightarrow D + \alpha \)
Where:
- P is the parent nucleus.
- D is the daughter nucleus formed after the emission of the alpha particle.
- \( \alpha \) is the alpha particle, which is the \( ^4_2He \) nucleus emitted from the parent nucleus.
The detailed equation with atomic and mass numbers is:
Example of Alpha Decay
Consider the decay of Radium-226, which decays by emitting an alpha particle to form Radon-222:
\( ^{226}_{88}Ra \xrightarrow{\text{α}} ^{222}_{86}Rn + ^4_2He \)
In this decay process, the parent nucleus is Radium-226 (\( ^{226}_{88}Ra \)). Upon emission of an alpha particle (\( ^4_2He \)), it transforms into Radon-222 (\( ^{222}_{86}Rn \)).
The atomic number decreases by 2, and the mass number decreases by 4:
- Radium's atomic number: \( Z = 88 \to Z = 86 \)
- Radium's mass number: \( A = 226 \to A = 222 \)
Radon-222 Decay to Polonium-218
Radon-222 itself is radioactive and decays further into Polonium-218 by emitting another alpha particle:
\( ^{222}_{86}Rn \xrightarrow{\text{α}} ^{218}_{84}Po + ^4_2He \)
Here, Radon-222 (\( ^{222}_{86}Rn \)) emits an alpha particle and transforms into Polonium-218 (\( ^{218}_{84}Po \)). The atomic number of Radon decreases by 2 (from 86 to 84), and the mass number decreases by 4 (from 222 to 218).
Characteristics of Alpha Particles
- Energy: Alpha particles typically have kinetic energies ranging between 4 to 9 MeV.
- Range in Air: The range of alpha particles in air is between 1 and 10 cm.
- Range in Tissue: In biological tissues, alpha particles have a range of 10 to 100 micrometers (µm).
Summary of Alpha Decay
In summary, alpha decay involves the following steps:
- Radium-226 decays into Radon-222 by emitting an alpha particle.
- Radon-222 further decays into Polonium-218 by emitting an alpha particle.
In both cases, the atomic number decreases by 2, and the mass number decreases by 4. The emitted alpha particles carry away a significant amount of energy in the form of kinetic energy, typically ranging between 4 to 9 MeV.
Impact of Alpha Decay
- Alpha particles have low penetration power, meaning they cannot penetrate the outer layers of skin. However, if alpha-emitting materials are inhaled or ingested, they can pose a serious health risk due to their high ionizing power.
- Alpha decay plays a significant role in the production of radon gas, which is a known health hazard when accumulated in poorly ventilated areas.
- While alpha decay is crucial in understanding natural radioactive processes, it is also important in various nuclear applications, including radiation protection and medicine.