When a radioactive atom emits an alpha particle, the original atom’s atomic number decreases by two (because of the loss of two protons), and its mass number decreases by four (because of the loss of four nuclear particles). (We often use 2 4He to represent an alpha particle.) It has a 2+ charge.

An alpha particle is composed of two protons and two neutrons and is the same as a helium nucleus. The first is called an alpha particle, which is symbolized by the Greek letter α. Rutherford’s experiments demonstrated that there are three main forms of radioactive emissions. The alpha particle removes two protons (green) and two neutrons (gray) from the uranium-238 nucleus.ģ.1 Major Forms of Radioactivity Alpha Particle (α) 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 (Figure 3.1).įigure 3.1 A nucleus of uranium-238 (the parent nuclide) undergoes α decay to form thorium-234 (the daughter nuclide). The daughter nuclide may be stable, or it may decay itself.

The unstable nuclide is called the parent nuclide the nuclide that results from the decay is known as the daughter nuclide. The spontaneous change of an unstable nuclide into another is radioactive decay. 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. 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. These emanations were ultimately called, collectively, radioactivity.įollowing the somewhat serendipitous discovery of radioactivity by Becquerel, many prominent scientists began to investigate this new, intriguing phenomenon. Further investigations showed that the radiation was a combination of particles and electromagnetic rays, with its ultimate source being the atomic nucleus. He reasoned that the uranium compound was emitting some kind of radiation that passed through the cloth to expose the photographic plate. But in 1896, the French scientist Henri Becquerel found that a uranium compound placed near a photographic plate made an image on the plate, even if the compound was wrapped in black cloth. Radioactivity and Nuclear Chemistry 3.1 Major Forms of Radioactivity Alpha Particle (α) Beta Particle (β) Gamma Radiation (γ) Positron Emission (β + decay) and Electron Capture Nuclear Fission 3.2 Radioactive Half Lives 3.3 Biological Effects of Radiation Exposure 3.4 Uses of Radioactive Isotopes 3.5 Chapter Summary 3.6 ReferencesĪtomic theory in the nineteenth century presumed that nuclei had fixed compositions.

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