Radioactive decay
The emission of radiation from an unstable 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. may cause changes to the nucleus, including:
- an increase or decrease in its massThe amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). and/or
- a change in its electric chargeThe electrical state of an object, which can be positively charged or negatively charged.
Changes due to radioactive decay can be represented by balanced nuclear equations. The changes that happen depend on the type of radiation emitted.
Alpha decay
alpha particleSubatomic particle comprising two protons and two neutrons (the same as a helium nucleus). consist of 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.. Protons are positively charged. When a nucleus emits an alpha particle, these changes happen:
- the mass number decreases by 4
- the atomic number decreases by 2
- the nuclear charge decreases by 2
Example
Radon-219 decays into polonium-215 by emitting an alpha particle. This is the balanced equation for the reaction:
\(_{86}^{219}Rn \rightarrow _{84}^{215}Po + _{2}^{4}\alpha\)
Notice that:
- the mass number of the nucleus decreases by 4, from 219 to 215
- the atomic number of the nucleus decreases by 2, from 86 to 84
- the numbers at the top and bottom give the same totals on both sides
Polonium nucleiNuclei is the plural of nucleus. The nucleus is the central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. have 84 protons, so their nuclear charge is +84. They have two fewer protons than radon nuclei, which have 86 protons and so a nuclear charge of +86.
Beta decay
A beta particle An electron emitted from a radioactive atom. forms when a neutron changes into a proton and a high-energy electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. The proton stays in the nucleus but the electron leaves the atom as a beta particle. When a nucleus emits a beta particle, these changes happen:
- the mass number stays the same
- the atomic number increases by 1
- the nuclear charge increases by 1
Example
Carbon-14 decays into nitrogen-14 by emitting a beta particle. This is the balanced equation for the reaction:
\(_{6}^{14}C \rightarrow _{7}^{14}N + _{-1}^{~0}\beta\)
Notice that:
- the mass number of the nucleus stays the same, 14
- the atomic number of the nucleus increases by 1, from 6 to 7
- the numbers at the top and bottom give the same totals on both sides, as (7 - 1) = 6
Nitrogen nuclei have 7 protons, so their nuclear charge is +7. They have one more proton than carbon nuclei, which have 6 protons and so a nuclear charge of +6.
Gamma decay
gamma rayThe shortest wavelength and highest energy part of the EM spectrum. Produced by radioactive materials. are a type of electromagnetic radiationEnergy travelling as waves in the form of changing electrical and magnetic fields.. There is no change in mass or charge for this type of decay.
Gamma radiation transfers energy from the nucleus, so the symbol \(_{0}^{0}\gamma\) may appear in some balanced equations.