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Transcript
Bell Ringer: Define using the graphic organizer: Radioactivity alpha particle beta particle gamma ray half-life fission fusion tracer alpha decay beta decay cloud chamber bubble chamber Geiger counter background radiation. Nuclear Radiation Radioactivity The Strong Force • How do you suppose protons and neutrons are held together so lightly in the nucleus? • Another force, called the strong force, causes protons and neutrons to be attracted to each other. Radioactivity The Discovery of Radioactivity • In 1896, Henri Becquerel left uranium salt in a desk drawer with a photographic plate. • Later, when he developed the plate, he found an outline of the clumps of the uranium salt. • He hypothesized that the uranium salt had emitted some unknown invisible rays, or radiation, that had darkened the film. Radioactivity The Discovery of Radioactivity • Two years after Becquerel’s discovery, Marie and Pierre Curie discovered two new elements, polonium and radium, that also were radioactive. • After more than three years, they were able to obtain about 0.1 g of radium from several tons of pitchblende (uranium oxide minerals). Radioactivity • The process by which an unstable nucleus emits one or more particles of energy. • The released energy or particles are called nuclear radiation. Nuclear Decay • Produces nuclear radiation as a by product. • Process by which an element can transform into a different isotopes of the same element or change into an entirely new element. Types of Nuclear Radiation • Alpha and beta radiation are particles. Gamma radiation is an electromagneti c wave. Alpha Particles • Positive Charged Particle • Made up of 2 protons and 2 neutrons. • Has the same mass as a helium atom. • Emitted by some radioactive nuclei. • Ionizes material as it passes through it. • Most massive type of radiation. • Does not travel far through a substance. Nuclear Decay Alpha Particles • Notice that the alpha particle and its symbol is the same as a helium nucleus, . • An alpha particle has an electric charge of +2 and an atomic mass of 4. Nuclear Decay Smoke Detectors • Some smoke detectors give off alpha particles that ionize the surrounding air. Nuclear Decay Smoke Detectors • If smoke particles enter the ionized air, they will absorb the ions and electrons. The circuit is broken and the alarm goes off. Beta Particles • Negative Charged Particle • Emitted during the radioactive decay of neutrons. • Neutron decays into a proton and an electron. • The proton stays in the nucleus. • The electron is emitted. • Ionize material as it passes through. Beta Particles • Because the atom now has one more proton, it becomes the element with an atomic number one greater than that of the original element. • However, because the total number of protons and neutrons does not change during beta decay, the mass number of the new element is the same as that of the original element. • Travels farther through a material than alpha radiation. Nuclear Decay Gamma Rays • They have no mass and no charge and travel at the speed of light. • The properties of gamma rays are summarized in the table. Gamma Rays • • • • • High energy electromagnetic radiation. Are not made of matter. No electric charge. Does not ionize material. However, gamma rays cause more damage to biological molecules as they pass through living tissue. • Can travel far through a material. • Concrete has to be 2 meters thick to stop gamma rays. Alpha Decay • In alpha decay, two protons and two neutrons are lost from the nucleus. Nuclear Decay 18.2 Alpha Decay • The new element has an atomic number two less than that of the original element. • The mass number of the new element is four less than the original element. • In this decay, polonium emits an alpha particle and changes into lead. Nuclear Decay 18.2 Beta Particles • Nuclei that emit beta particles undergo Beta Decay. Nuclear Decay 18.2 Beta Decay • The new element has an atomic mass that is the same as the original element. • Because the atom now has one more proton, it becomes the element with an atomic number one greater than that of the original element. • However, because the total number of protons and neutrons does not change during beta decay, the mass number of the new element is the same as that of the original element. Nuclear Decay 18.2 Beta Decay • Nucleus gains a proton and loses a neutron -Ex. Iodine will decay to Xenon by emitting a beta particle.