Alpha, Beta, Gamma Decay — Core Principles

Core Principles

Radioactive decay is the spontaneous process by which unstable atomic nuclei transform into more stable forms by emitting radiation. The three primary types are alpha, beta, and gamma decay, each with distinct characteristics and effects on the nucleus.

Alpha decay involves the emission of a helium nucleus ($^4_2\text{He}$), reducing the atomic number (Z) by 2 and mass number (A) by 4. Beta decay involves the transformation of a nucleon: beta-minus ($\beta^-$) decay sees a neutron convert to a proton, emitting an electron ($e^-$) and an antineutrino, increasing Z by 1 while A remains constant.

Beta-plus ($\beta^+$) decay involves a proton converting to a neutron, emitting a positron ($e^+$) and a neutrino, decreasing Z by 1 while A remains constant. Electron capture is an alternative to beta-plus, where an inner electron is captured, converting a proton to a neutron, also decreasing Z by 1.

Gamma decay involves the emission of high-energy photons (gamma rays) from an excited nucleus, without changing A or Z, simply lowering the nucleus's energy state. These decays adhere to conservation laws of mass number, atomic number (charge), energy, and momentum.

The emitted radiations have varying ionizing and penetrating powers, crucial for their applications and hazards.

Important Differences

vs Alpha, Beta, and Gamma Radiations

Aspect	This Topic	Alpha, Beta, and Gamma Radiations
Nature	Alpha particle ($^4_2\text{He}$ nucleus)	Beta particle (electron $e^-$ or positron $e^+$)
Charge	+2e	-e ($\beta^-$) or +e ($\beta^+$)
Mass	Approx. 4 amu	Approx. $1/1836$ amu (electron mass)
Effect on Parent Nucleus (A, Z)	A decreases by 4, Z decreases by 2	A remains same, Z increases by 1 ($\beta^-$) or Z decreases by 1 ($\beta^+$)
Origin	Nucleus (emission of He nucleus)	Nucleus (transformation of n to p or p to n)
Ionizing Power	Very High	Moderate
Penetrating Power	Very Low (stopped by paper)	Moderate (stopped by aluminum)
Deflection in E/B fields	Significant (towards negative plate in E-field)	Significant (towards positive plate for $\beta^-$, negative for $\beta^+$ in E-field; greater curvature than alpha)
Speed	0.05-0.07c	Up to 0.99c

The three main types of radioactive decay, alpha, beta, and gamma, differ fundamentally in the nature of the emitted radiation, their charge, mass, and how they alter the parent nucleus. Alpha particles are heavy, positively charged helium nuclei, causing significant changes in both mass and atomic numbers. Beta particles are lighter electrons or positrons, altering only the atomic number. Gamma rays are massless, chargeless photons, which only de-excite the nucleus without changing its composition. These differences lead to vastly different ionizing and penetrating powers, and distinct behaviors in electric and magnetic fields, which are critical for their detection, shielding, and applications.