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Radioactivity
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Radioactivity is a physical, not a biological, phenomenon. Simply stated, the radioactivity of a sample can be measured by counting how many atoms are spontaneously decaying each second. This can be done with instruments designed to detect the particular type of radiation emitted with each "decay" or disintegration. The actual number of disintegrations per second may be quite large. Scientists have agreed upon common units to use as a form of shorthand. Thus, a curie (abbreviated "Ci" and named after Pierre and Marie Curie, the discoverers of radium[87]) is simply a shorthand way of writing "37,000,000,000 disintegrations per second," the rate of disintegration occurring in 1 gram of radium.
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Radioactivity is the phenomenon where elements release energy due to the instability of the nucleus. There are three types of radiation. The first is alpha radiation. Alpha radiation is when helium nuclei, or protons, are emitted at high speeds from a radioactive element. Because alpha particles are relatively large, they have little power to penetrate objects, and are not considered to be very harmful.
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Radioactivity has nothing to do with active radios! It is the breaking up of particles or nuclei into smaller ones. These go shooting off at high speed, hitting other nuclei and making them hot. All the smaller particles which are produced are called radiation, hence the name. Because of the energy released, radioactive decay releases heat. It is the source of heat in the Earth, keeping the core hot, and causing continental drift.
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Radioactivity occurs when an atomic nucleus breaks down into smaller particles. There are three types of particles: alpha, beta, and gamma. Alpha particles are positively charged, beta particles are negatively charged, and gamma particles have no charge. The particles ... have increasing levels of energy, first Alpha, then Beta, and finally Gamma, which is the fastest and most energetic of all the emission particles.
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Radioactivity can occur both naturally and through human intervention. An example of artificially induced radioactivity is neutron activation. A neutron fired into a nucleus can cause nuclear fission (the splitting of atoms). This is the basic concept behind the atomic bomb. Neutron activation is ... the underlying principle of boron-neutron capture therapy for certain brain cancers. A solution containing boron is injected into a patient and is absorbed more by the cancer than by other cells.
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Radioactivity was first discovered in 1896 by the French scientist Henri Becquerel, after which the SI unit for radiation, the Becquerel, is named. Becquerel discovered that uranium salts were able to blacken a photographic plate placed in the dark, even through a paper barrier. Subsequent experiments distinguished three distinct types of radiation -- alpha particles, beta particles, and gamma rays. These are positively charged, negatively charged, and neutral, respectively. In the United States, human exposure to radioactivity is measured in rads, where one rad represents 0.01 joule of energy absorbed per kilogram of tissue.
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