Radioactivity

RADIOACTIVITY AND WCLEM CHEMISTRY
Previously we learned that there are isotopes of almost all the elements. Most of these isotopes are stable, but some are unstable. The nuclei of unstable isotopes undergo spontaneous nuclear reactions that cause particles and energy, called nuclear radiation, to be given off. The emission of these particles and energy by an isotope is called radioactivity. Only a few isotopes found in nature are radioactive. The first example of a naturally occurring radioactive substance was discovered by Henri Becquerel in 1896. He found that uranium ore gave off penetrating radiation that darkened photographic film without exposing the film to light. Since then, other scientists have found many other radioactive elements. More than 50 naturally occurring radioactive isotopes are now known. In addition, scientists have been able to make many radioactive isotopes not found in nature.
The discovery of radioactive isotopes has greatly affected our lives. The awesome power of nuclear weapons, the promise of abundant energy, radiation therapy, and contamination of the environment by nuclear waste products are all results of the properties of the tiny nuclei of these radioactive isotopes. TYPIES OF RADIATION
Early in the twentieth century, it was discovered that naturally occurring isotopes emit three kinds of radiation. At that time, scientists did not understand them, so their discoverers named them simply alpha (a) beta (p) and gamma (y). Since then, scientists have discovered the identities and properties of these types of radiation. Each has characteristic properties that determine how it affects living systems
Alpha radiation is a stream of particles moving at about one-tenth the speed of light. Each particles is the nucleus of helium atom that contains two protons and two neutrons and has a charge of +2. Alpha particles are relatively large and heavy, so they cannot travel very far without colliding with other particles. As a result these particles do little damage to internal organs because they cannot penetrate the skin. However, if a substance that emits alpha particles gets inside the body by being inhaled or swallowed, the alpha particles can then damage internal organ.
Beta radiation is also a stream of particles, but the particles are electrons. The electrons are produced within the nucleus by the transformation of a neutron into a proton and an electron. The proton stays in the nucleus and the electron is emitted. An electron is smaller than a helium nucleus (alpha particle), travels much faster, and can penetrate the skin to a depth of a few centimeters. Exposure to beta radiation causes the skin to appear burned. Damage to internal organs occurs when a substance that emits beta particles gets into the body.
Gamma radiation is not a particle, but a form of energy similar to light waves, radio waves, or x-rays. This radiation has high energy and can penetrate deep within the body and cause serious damage. Gamma radiation usually occurs along with alpha and beta radiation.
Two less common but still important types of nuclear radiation are neutrons
and positrons. A positron has about the same mass as an electron but has a positive charge. The properties and symbols of these various forms of radiation are summarized in Tablel. The emission of radiation from radioactive isotopes is also called ionizing radiation.