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Alpha decay is by far the most common form of cluster decay, where the parent atom ejects a defined daughter collection of nucleons, leaving another defined product behind. It is the most common form because of the combined extremely high nuclear binding energy and relatively small mass of the alpha particle.
Alpha particle emissions are generally produced in the process of alpha decay. Alpha particles are a strongly ionizing form of radiation, but when emitted by radioactive decay they have low penetration power and can be absorbed by a few centimeters of air, or by the top layer of human skin.
Alpha decay can provide a safe power source for radioisotope thermoelectric generators [29] used for space probes. Alpha decay is much more easily shielded against than other forms of radioactive decay. Plutonium-238, a source of alpha particles, requires only 2.5 mm of lead shielding to protect against unwanted radiation.
Any decay daughters that are the result of an alpha decay will also result in helium atoms being created. Some radionuclides may have several different paths of decay. For example, 35.94(6) % [27] of bismuth-212 decays, through alpha-emission, to thallium-208 while 64.06(6) % [27] of bismuth-212 decays, through beta-emission, to polonium-212.
This means that alpha particles from ordinary alpha decay do not penetrate the outer layers of dead skin cells and cause no damage to the live tissues below. Some very high energy alpha particles compose about 10% of cosmic rays , and these are capable of penetrating the body and even thin metal plates.
The negatively charged electrons and positively charged ions created by ionizing radiation may cause damage in living tissue. Basically, a particle is ionizing if its energy is higher than the ionization energy of a typical substance, i.e., a few eV, and interacts with electrons significantly.
In nuclear and materials physics, stopping power is the retarding force acting on charged particles, typically alpha and beta particles, due to interaction with matter, resulting in loss of particle kinetic energy. [1] [2] Stopping power is also interpreted as the rate at which a material absorbs the kinetic energy of a charged particle.
An example is presented in the figure to the right. The periodic abrupt decrease in ionization potential after rare gas atoms, for instance, indicates the emergence of a new shell in alkali metals . In addition, the local maximums in the ionization energy plot, moving from left to right in a row, are indicative of s, p, d, and f sub-shells.