3.1 Alpha decay and its characteristics

Alpha decay is a crucial radioactive process where heavy nuclei emit alpha particles. These helium nuclei, consisting of two protons and two neutrons, play a significant role in nuclear stability and energy release.

Understanding alpha decay helps explain radioactive transformations and nuclear structure. This knowledge is essential for applications in nuclear physics, radiotherapy, and environmental monitoring, connecting to broader concepts of radioactive decay modes.

Composition and Properties of Alpha Particles

Structure and Characteristics of Alpha Particles

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• Consist of two protons and two neutrons, equivalent to a helium nucleus ($^4_2He^{2+}$)
• Have a mass of approximately 4 atomic mass units and a charge of +2
• Emitted from the nucleus of an atom during alpha decay, a type of radioactive decay
• Possess high ionization power due to their relatively large mass and charge

Factors Influencing Alpha Particle Emission

• Nuclear stability determines the likelihood of alpha decay occurring in a given isotope
• Isotopes with an excess of protons or a large atomic number are more likely to undergo alpha decay to achieve a more stable nuclear configuration
• The Q-value represents the energy released during alpha decay and is equal to the difference in binding energies between the parent and daughter nuclei
• A positive Q-value indicates that the decay is energetically favorable and will occur spontaneously

Alpha Particle Interactions with Matter

Penetration and Range of Alpha Particles

• Alpha particles have a relatively short range in matter due to their large mass and charge
• The tunneling effect allows alpha particles to escape the potential barrier of the nucleus, even when their energy is lower than the barrier height
• The range of alpha particles depends on the initial energy and the density of the material they traverse (a few centimeters in air, micrometers in solid materials)
• The Bragg curve describes the energy loss of alpha particles as they travel through matter, with a sharp peak in energy deposition near the end of their range

Ionization and Energy Deposition

• Alpha particles interact strongly with matter, causing ionization and excitation of atoms along their path
• The high specific ionization of alpha particles results in dense tracks of ionization, leading to localized damage in materials and biological tissues
• The linear energy transfer (LET) of alpha particles is high, meaning they deposit a large amount of energy per unit path length
• Alpha particles are often used in targeted radiation therapy (alpha therapy) due to their ability to deliver high doses of radiation to small volumes of tissue