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Band of Stability. Chart of the Isotopes As the atomic number increases, more neutrons are needed to make the nucleus stable Clues to radioactivity: Atomic number of 83 and above Fewer neutrons than protons in the nucleus Odd-Odd nuclide. U-238 Decay. Nuclear Fission.
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Band of Stability Chart of the Isotopes As the atomic number increases, more neutrons are needed to make the nucleus stable Clues to radioactivity: Atomic number of 83 and above Fewer neutrons than protons in the nucleus Odd-Odd nuclide
Nuclear Fission When a nucleus fissions, it splits into several smaller fragments. Two or three neutrons are also emitted. The sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy. Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously.
Fission-Continued... A chain reaction occurs when neutrons released in fission produce an additional fission in at least one further nucleus. This nucleus in turn produces neutrons, and the process repeats.
Control of Fission To maintain a sustained controlled reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium nucleus. Nuclear reactions are controlled by a neutron-absorbing material, such as cadmium or graphite.
Nuclear Fusion Fusion is combining the nuclei of light elements to form a heavier element. In a fusion reaction, the total mass of the resultant nuclei is slightly less than the total mass of the original particles.
Fusion In order for fusion reactions to occur, the particles must be hot enough, in sufficient number and well contained. These simultaneous conditions are represented by a fourth state of matter known as plasma. In a plasma, electrons are stripped from their nuclei. A plasma, therefore, consists of charged particles, ions and electrons.
Fusion Magnetic confinement utilizes strong magnetic fields, typically 100,000 times the earth's magnetic field. Inertial confinement uses powerful lasers or high energy particle beams to compress the fusion fuel. The enormous force of gravity confines the fuel in the sun and stars.
Fusion Reactors Themost successful and promising fusion confinement device is known as a tokamak. This donut-shaped configuration is characterized by a large current, up to several million amperes, which flows through the plasma. The plasma is heated to temperatures more than a hundred million degrees centigrade by high-energy particle beams or radio-frequency waves.
Fusion-Waste Products The deuterium in the earth's oceans is sufficient to fuel advanced fusion reactors for millions of years. The waste product from a deuterium-tritium fusion reactor is ordinary helium.
Fundamental Particles Quarks make up protons and neutrons, which, in turn, make up an atom's nucleus. Each proton and each neutron contains three quarks. There are several varieties of quarks, as seen to the right. Protons and neutrons are composed of two types: up quarks and down quarks. The sum of the charges of quarks that make up a nuclear particle determines its electrical charge.
Building an Atom Protons contain two up quarks and one down quark. +2/3 +2/3 -1/3 = +1 Neutrons contain one up quark and two down quarks. +2/3 -1/3 -1/3 = 0 The nucleus is held together by the "strong nuclear force," which is one of four fundamental forces The strong force counteracts the tendency of the positively-charged protons to repel each other. It also holds together the quarks that make up the protons and neutrons. http://cgi.pbs.org/wgbh/aso/tryit/atom/
Antimatter Antimatter is matter with a charge opposite to that of what we think of as normal matter, such as: Electron, Positron, Proton, Anti-proton, and Neutron , Anti-neutron, etc. Antiparticles act in much the same way as do ordinary particles Each has the same mass as their counterparts, but the charge is opposite. If any particle touches it's corresponding antiparticle both would be totally annihilated leaving only energy.
Cosmic Rays Cosmic rays hitting the outer atmosphere are mainly fast-moving, high-energy protons. As they hurtle towards the Earth, they collide with atoms in the air. Some of the collision energy reappears as the mass of new pairs of particles and antiparticles. Cosmic rays are thus a natural source of antiparticles - and in 1932 Carl Anderson's studies of cosmic rays revealed the first antiparticle ever seen, the anti-electron, or "positron".
Applications of Antimatter Particle physicists regularly use collisions between electrons and their antiparticles, positrons, to investigate matter and fundamental forces at high energies. At low energies, however, the electron-positron annihilations can be put to different uses, for example to reveal the workings of the brain in the technique called Positron Emission Tomography (PET). In PET, the positrons come from the decay of radioactive nuclei The positrons then annihilate with electrons in nearby atoms, producing gamma rays
