Further Modes of Decay

Submitted by ChemPRIME Staff on Thu, 12/16/2010 - 15:58


Isotopes produced by nuclear reactions which do not occur in nature (artificial isotopes) are invariably unstable and radioactive. They exhibit two kinds of decay not found among naturally occurring radioactive elements. The first is positronA positively charged particle having the same mass and magnitude of charge as an electron. emission (also called β+ emission) in which a fundamental particle we have not discussed is ejected from the nucleus. The positron is identical with the electron except that it has a positive rather than a negative charge. Its symbol is 0+1e. An example of positron emission is


{}_{\text{6}}^{\text{11}}\text{C }\to \text{ }{}_{\text{5}}^{\text{11}}\text{B + }{}_{\text{+1}}^{\text{0}}e      (1)


Positron emission is common among isotopes having a low neutronThe uncharged particle in an atomic nucleus; its mass is similar to the mass of a hydrogen atom.-to-protonThe positively charged particle in an atomic nucleus; its mass is similar to the mass of a hydrogen atom. ratio.

The second new method of decay is called electron captureA type of radioactive decay in which an electron from an inner shell of an atom is absorbed by the nucleus. In the process a proton is converted into a neutron and the atomic number of the element decreases by one. Also called K capture, because the electron comes from the 1s orbital (K shell).. The nucleus absorbs one of the electrons from its own innermost core. An example is the following reaction:


{}_{-\text{1}}^{\text{0}}e\text{ + }{}_{\text{4}}^{\text{7}}\text{Be }\xrightarrow{ec}\text{ }{}_{\text{3}}^{\text{7}}\text{Li}      (2)


Again this results in an increased neutron/proton ratio.