Radioactive Decay
Radioactive Decay
Radioactive Decay
Alpha decay (пЃЎ) is the emission of an alpha particle from an atom’s nucleus; it contains two protons and two neutrons – which is equivalent to a helium-4 nucleus. When an atom emits anпЂ пЃЎ particle, the atoms atomic mass will decrease by four (because two protons and two neutrons are lost) and the atomic number will decrease by two. An example of alpha decay takes place when uranium decays into thorium by emitting an alpha particle.
Beta decay (ОІ) is the conversion of a neutron into a proton and an electron, where the electron is expelled from the atom as a ОІ-particle. When this occurs the mass of the atom will not change, though the atomic number will increase by one, since there is an additional proton, an example of this is the decay carbon-14 into the nitrogen.
Natural radioactive decay works according to the principle of half-life; this is the amount of time needed for one-half of the radioactive substance to decay. In contrast, nuclear fission is the splitting of an atoms’ nucleus into smaller parts, releasing a large amount of energy in the process. (The energy produced is from the direct conversion of matter into energy, according to Einstein’s equation E=mc2). This is usually done by firing a neutron at the atoms’ nucleus. The energy of the neutron makes the intended element to divide into free neutrons and two (or more) smaller nuclei.
Under the extremely high temperatures and pressures within the core of stars, atoms collide at high speeds that overcome the electromagnetic repulsion of nuclei, allowing nuclear fusion. In the initial step of the procedure, two hydrogen atoms fuse to create deuterium. Subsequently, another hydrogen atom fuses with the deuterium, creating an isotope of helium that has two protons and one neutron. In the final step, both the isotopes fuse to produce a normal helium atom and a normal hydrogen nucleus. Elements such as lithium are made from these two elements in a range of procedures called nucleogenesis. As stars evolve, they run out of hydrogen, so they fuse helium nuclei to form other heavier elements e.g. carbon, oxygen etc. The enormous luminous energy of the stars comes from nuclear fusion processes in their
centres.
During the Big Bang4He + 3H→7Li occurred primarily, and the 4He + 3He +e → 7Be + e → 7Li occur in normal stars. The other results of Lithium production are the spallation of heavier nuclei using cosmic rays. E.g. 11Boron, although stable, could be made to emit an alpha particle if excited by the proper energy cosmic ray: 11B + γ → 7Li + 4He
The absorption of a neutron by 235U induces oscillations in the nucleus that deform it until it splits into fragments.
Nuclear fission can be controlled via a chain reaction where free neutrons released by each fission event can trigger more occurrences, which in turn release more neutrons and cause more fission. To prolong a sustained controlled nuclear reaction at least one neutron released, must strike another uranium nucleus. If this ratio is less than one then the reaction will die out; if it is greater, it will grow uncontrolled
(an atomic explosion). Most reactors are controlled by control rods that are made of neutron-absorbent material e.g. boron.
(Uranium split into lanthanum and bromine nuclei)
The most common nuclear fuels are 235U and 239Pu. In a nuclear reactor, most fission events are generated by bombardment with a neutron. The energy of nuclear fission is released as kinetic energy of the fission products, and as gamma rays. In a nuclear reactor, the energy is converted to heat as the particles and gamma rays collide with the atoms that the reactor is made of, and its working fluid, usually water.
Nuclear fusion is when two or more elements join together to form one larger element, releasing tremendous amounts of energy in the process. An example is the fusion of two “heavy” isotopes of hydrogen (deuterium: H2 and tritium: H3) into the element helium. It takes a substantial amount of energy to force nuclei to fuse, this is because all nuclei are positively charged, and nuclei strongly resist being put too close together. Accelerated to high speeds, however, they can overcome this electromagnetic repulsion and get close enough to achieve fusion. The fusion of nuclei will normally release more energy than it took to force them together.