Radioactive decay
A nucleus changes into a new element by emitting alpha particleSubatomic particle comprising two protons and two neutrons (the same as a helium nucleus). or betaA type of ionising radiation consisting of a single electron. particles. These changes are described using nuclear equations.
Alpha decay (two protonSubatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. and two neutronUncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0.) changes the mass numberThe number of protons and neutrons found in the nucleus of an atom. of the element, decreasing by four and decreasing the atomic numberThe number of protons in the nucleus of an atom. Also called the proton number. by two. An alpha particle is the same as a helium-4 nucleusThe central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei..
Example
\(_{86}^{219}\textrm{Rn} \rightarrow _{84}^{215}\textrm{Po} + _{2}^{4}\textrm{He}\)
Beta decay changes the atomic number, increasing by one (the nucleus gains a proton) but the mass number remains unchanged (it gains a proton but loses a neutron by ejecting an electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons., so a beta particle is an electron).
Example
\(_{6}^{14}\textrm{C} \rightarrow _{7}^{14}\textrm{N} + _{-1}^{0}\textrm{e}\)
gamma radiationA type of ionising radiation that is also part of the EM spectrum. It has no mass. is pure energy and will not change the structure of the nucleus in any way.
Question
Uranium 238, \(_{92}^{238}\textrm{U} \), emits an alpha particle to become what nucleus?
Alpha decay (two protons and two neutrons) decreases the mass number of the element by four and decreases the atomic number by two, so the remaining nucleus will be \(_{90}^{234}\textrm{}\).
A periodic table shows that element number 90 is thorium, \(_{90}^{234}\textrm{Th} \).