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By the end of this section, you will be able to:
  • Recognize common modes of radioactive decay
  • Identify common particles and energies involved in nuclear decay reactions
  • Write and balance nuclear decay equations
  • Calculate kinetic parameters for decay processes, including half-life
  • Describe common radiometric dating techniques

Following the somewhat serendipitous discovery of radioactivity by Becquerel, many prominent scientists began to investigate this new, intriguing phenomenon. Among them were Marie Curie (the first woman to win a Nobel Prize, and the only person to win two Nobel Prizes in different sciences—chemistry and physics), who was the first to coin the term “radioactivity,” and Ernest Rutherford (of gold foil experiment fame), who investigated and named three of the most common types of radiation. During the beginning of the twentieth century, many radioactive substances were discovered, the properties of radiation were investigated and quantified, and a solid understanding of radiation and nuclear decay was developed.

The spontaneous change of an unstable nuclide into another is radioactive decay    . The unstable nuclide is called the parent nuclide    ; the nuclide that results from the decay is known as the daughter nuclide    . The daughter nuclide may be stable, or it may decay itself. The radiation produced during radioactive decay is such that the daughter nuclide lies closer to the band of stability than the parent nuclide, so the location of a nuclide relative to the band of stability can serve as a guide to the kind of decay it will undergo ( [link] ).

A diagram shows two spheres composed of many smaller white and green spheres connected by a right-facing arrow with another, down-facing arrow coming off of it. The left sphere, labeled “Parent nucleus uranium dash 238” has two white and two green spheres that are near one another and are outlined in red. These two green and two white spheres are shown near the tip of the down-facing arrow and labeled “alpha particle.” The right sphere, labeled “Daughter nucleus radon dash 234,” looks the same as the left, but has a space for four smaller spheres outlined with a red dotted line.
A nucleus of uranium-238 (the parent nuclide) undergoes α decay to form thorium-234 (the daughter nuclide). The alpha particle removes two protons (green) and two neutrons (gray) from the uranium-238 nucleus.

Types of radioactive decay

Ernest Rutherford’s experiments involving the interaction of radiation with a magnetic or electric field ( [link] ) helped him determine that one type of radiation consisted of positively charged and relatively massive α particles; a second type was made up of negatively charged and much less massive β particles; and a third was uncharged electromagnetic waves, γ rays. We now know that α particles are high-energy helium nuclei, β particles are high-energy electrons, and γ radiation compose high-energy electromagnetic radiation. We classify different types of radioactive decay by the radiation produced.

A diagram is shown. A gray box on the left side of the diagram labeled “Lead block” has a chamber hollowed out in the center in which a sample labeled “Radioactive substance” is placed. A blue beam is coming from the sample, out of the block, and passing through two horizontally placed plates that are labeled “Electrically charged plates.” The top plate is labeled with a positive sign while the bottom plate is labeled with a negative sign. The beam is shown to break into three beams as it passes in between the plates; in order from top to bottom, they are red, labeled “beta rays,” purple labeled “gamma rays” and green labeled “alpha rays.” The beams are shown to hit a vertical plate labeled “Photographic plate” on the far right side of the diagram.
Alpha particles, which are attracted to the negative plate and deflected by a relatively small amount, must be positively charged and relatively massive. Beta particles, which are attracted to the positive plate and deflected a relatively large amount, must be negatively charged and relatively light. Gamma rays, which are unaffected by the electric field, must be uncharged.

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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