Radioactive Decay

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Radioactive Decay

This lesson aligns with NGSS PS1.C

Introduction

The phenomenon of radioactive decay stands as a fundamental and intriguing process that governs the stability and transformation of atomic nuclei. Nuclei with an imbalance of protons and neutrons seek a more stable configuration by undergoing radioactive decay. During this process, a radioactive nucleus spontaneously transforms into a different nucleus, emitting particles or electromagnetic radiation in the form of alpha or beta particles, gamma rays, or positrons. This article aims to learn about radioactive decay, radioactive decay law and types of radioactive decay.

Radioactive Decay

In the year 1896, A.H. Becquerel made an accidental discovery—radioactivity. Engaged in the study of fluorescence and phosphorescence of compounds irradiated with visible light, Becquerel observed an intriguing phenomenon during his experiments.

Becquerel conducted an experiment in which he exposed Uranium-Potassium-Sulphate to visible light. Following this, he carefully covered these illuminated pieces with black paper, separated it from a photographic plate by a piece of silver. After allowing the setup to sit for several hours, the photographic plate was developed, revealing distinct blackening on its surface.

This indicated that the compound emitted a form of radiation capable of penetrating both the silver layer and the black paper, ultimately reaching the photographic plate. Subsequent experiments conducted by Becquerel and others led to the conclusion that radioactivity is a nuclear phenomenon. It occurs when an unstable nucleus undergoes a process of decay, aptly termed "Radioactive Decay."

Types of Radioactive Decay

There are three types of radioactive decay.

Alpha decay
Beta decay
Gamma decay

Alpha Decay

When an alpha particle emits its nucleus, this phenomenon is termed alpha decay. The expression representing alpha decay is formulated as follows:

Where,

[math]m_i[/math] is the initial mass of the nucleus
[math]m_f[/math] is the mass of the nucleus after particles emission
[math]m_p[/math] is the mass of the emitted particle

The nucleus of helium serves as the exceptionally stable alpha particle, consisting of a group of two protons and two neutrons. To illustrate, the alpha decay of uranium-238 can be exemplified as follows:

Transmutation is the term used to describe the process by which isotopes undergo a transformation into an element with a stable nucleus.

Beta Decay

A beta particle is commonly known as an electron, although it can alternatively be a positron. When the reaction involves electrons, the nucleus releases neutrons individually, causing an increase in the proton number.

Beta decay involves the transformation of a neutron into a proton or vice versa.
Two types of beta decay exist: beta-minus (β−) and beta-plus (β+) decay.

Example: Carbon-14 undergoing beta decay transforms into Nitrogen-14.

The process of beta decay is illustrated below:

Gamma Decay

Within the nucleus, electrons orbit, possessing inherent energy. When an electron shifts from a high-energy level to a lower one, it emits a photon. Analogously, within the nucleus, the emission of a high-energy photon occurs whenever the nucleus rearranges itself to a lower energy level, this is known as gamma ray.

Gamma decay is the emission of gamma rays from an excited nucleus.
Unlike alpha and beta particles, gamma rays are electromagnetic radiation with no mass or charge.

Example: After alpha or beta decay, the resulting nucleus may be in an excited state and emit gamma rays to achieve a lower energy state.

Summary

The phenomenon occurs when an unstable nucleus undergoes a process of decay, which is termed "Radioactive Decay."
When an alpha particle emits its nucleus, this phenomenon is termed alpha decay.
Beta decay involves the transformation of a neutron into a proton or vice versa.
Gamma decay is the emission of gamma rays from an excited nucleus.

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