Radioactive Disintegration: Alpha Decay and Beta Decay

Radioactive disintegration is the spontaneous breakdown of the nucleus of an atom. This is also expressed quantitatively as Decay. The disintegration of the nuclei of radioactive atoms is accompanied by the emission of two particles: Alpha particle (α-particle) and Beta particle (β-particle). But there is also the emission of a third substance called the Gamma-ray (γ-rays) which sometimes accompany the emission of α and β-particles.

Radioactive disintegration result to the formation of a new element by a process of transmutation. But natural radioactive transmutation is spontaneous and different from artificial transmutation. But what is most interesting is how the condition of radioactive reactions differ from ordinary chemical reaction. For example, no physical or chemical process can alter the rate of disintegration. That is, a radioactive material will disintegrate in the same rate in Ice and in a temperature of 200°C. Also, the rate of decay depends on the substance and vary from material to material.

Now let's consider Alpha and Beta Decay in details.

Alpha particle (α-particle) is simply a Helium nucleus (⁴₂He). Hence the nucleus of an atom is reduced by a mass number of four units and an atomic number of two units when it losses an alpha particle during disintegration. This results to the formation of a new element that is two places to the left of the original element. Alpha particle decay or disintegration can be expressed by the general formula:

^A_ZX → ^(A-4)_(Z-2)Y + ⁴₂He

Where,

^A_ZX is the parent nuclei with a mass number: A, and atomic number Z; ^(A-4)_(Z-2)Y is the daughter nucleus with mass number (A-4) and atomic number (Z-2); and ⁴₂He is the emitted Alpha particle usually expressed as α in some equations.

The alpha-breakdown of Uranium can be substituted as an example into the general equation. Here, Uranium-238 nucleus spontaneously emits an α-particle to form the nucleus of a new element, Thorium-234.

²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He

The formation of Thorium from Uranium actually confirm the notion that alpha-decay usually result to the reduction of the mass number by four units and atomic number by two units.

The emission of the Beta Particle (β-particle) is equivalent to the loss of an electron, which otherwise interprets to an increase in the number of proton by one unit. Although the mass number is unaltered, a new element whose property is similar to an element one step above the disintegrated element in the periodic table.

The general equation for α-decay is as represented in:

^A_ZX → ^A_(z+1)Y + ⁰_-1e

Where, ^A_ZX is the parent nucleus, ^A_(z+1)Y is the daughter nucleus, and ⁰_-1e is the emitted β-particle.

An example of the Emission of β-particle is the β-decay of Thorium-234 to Protactinium-234:

²³⁴₉₀Th → ²³⁴₉₁Pa + ⁰_-1e

Here, you see that the mass number of Thorium and Protactinium are the same, except that the atomic number of protactinium is increased by one unit from 90 to 91.