Alpha Decay and Characteristics of Alpha Particles

Alpha Decay

Concept of Alpha Decay

Alpha decay is a type of radioactive decay in which an unstable nucleus emits an alpha particle. This process is common among heavy nuclei and results in the formation of a new element with a lower atomic number and mass number.

• Alpha Particle: Consists of 2 protons and 2 neutrons, identical to a helium-4 nucleus. It is usually symbolized as 4He2 or 4α2.

• Effect on Nucleus: The emission of an alpha particle reduces the atomic number by 2 and the mass number by 4.

General Equation for Alpha Decay:

$^A_ZX \rightarrow ^{A-4}_{Z-2}Y + ^4_2He$

• Balancing Nuclear Reactions: When writing nuclear equations, both the mass number (A) and atomic number (Z) must be balanced on both sides of the equation.

Example: Write a balanced nuclear reaction for alpha decay of 238U.

$^{238}_{92}U \rightarrow ^{234}_{90}Th + ^4_2He$

Characteristics of Alpha Particles

• Ionizing Power: Alpha particles have high ionizing power, meaning they can easily remove electrons from atoms and molecules.

• Penetrating Power: Alpha particles have low penetrating power and can be stopped by a sheet of paper or even the outer layer of human skin.

Types of Radioactivity (Table)

The following table summarizes the main types of radioactive emissions, their symbols, charges, and relative properties.

Type	Symbol	Charge	Largest Penetrating Power	Largest Ionizing Power	Damage to Biological Tissues
Alpha	$^4_2He$	+2	Lowest	Highest	Low (unless ingested/inhaled)
Beta	$^0_{-1}e$	-1	Intermediate	Intermediate	Moderate
Gamma	$\gamma$	0	Highest	Lowest	High

Summary of Alpha Decay Effects

• When an alpha particle is emitted, the mass number (A) decreases by 4 and the atomic number (Z) decreases by 2.

• Alpha decay typically occurs in heavy, unstable nuclei.

• Alpha particles are not very penetrating but are highly ionizing.

Example: Select the correct statement about alpha decay:

• Alpha decay reduces the atomic number by 2 and the mass number by 4.

• Alpha particles are identical to helium-4 nuclei.

• Alpha particles have high ionizing power but low penetrating power.