RADIOACTIVE DECAY

• Every  Element has One or More Isotopes that have Unstable Nuclei that are Subject to radioactive decay, causing the Nucleus to emit particles or Electromagnetic radiation.
• Radioactivity can occur when the Radius of a Nucleus is large compared with the radius of the Strong forces, which only acts over distances on the order of 1fm.  

• THE MOST COMMON FORMS OF RADIOACTIVE DEACY ARE: 

•  ALPHA decay is caused when the nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two Neutrons.
• The result of the emission is a new element with a lower atomic number.
•  BETA decay (and electron capture) are regulated by the weak forces, and result from a transmission of neutron into a proton, or a proton into a neutron.
• The first is accompained by the emission of an electron and an antineutrino. 
• while the second causes the emission of a position and a neutrino.
• The Electron or positron emission are called beta particles.
• Beta  decay either incerases or decreases  the atomic number of the nucleus by one.
• An analog of  positron beta decay in nuclei that are proton-rich is electron capture, a process even more common than positron emission since it requires less energy.
• In this type of decay an electron is absorbed by the nucleus, rather than a positron emitted.
• A neutrino is still emitted in this process, and a proton again changes to a neutron.
• GAMMA decay results from a change in the energy level of the nucleus to a lower state, resulting in the emission of electromagnetic radiation.
• This can occur following the emission of an alpha or a beta particle form radioactive decay.

• Other more rare type of radioactive decay include ejection of neutrons or protons or clusters of nucleons from a nucleus, or more than one beta particle, or result (through internal conversion) in production of high-speed electrons that are not beta rays, and high-energy photons that are not gamma rays.
• A few large nuclei explode into two or more charged fragments of varying  masses plus several neutrons, in a decay called spontaneous nuclear fission. 
• Each radiactive isotope has a characteristic decay time period - the half-life - that is determined by the amount of time needed for half of a sample to decay.
• This is an exponential decay process that steadily decreases the proportion of the remaining isotope by 50% every half-life.
• Hence, after two half-lives have passed only 25% of the isotope is present, and so forth.

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