Astrophysics (Index)About

isotope

(subclass of an element with a specific number of nucleons)

An isotope is a subclass of an element with a specific number of nucleons, i.e., protons and neutrons. The number of protons (atomic number) determines the element, and given that, the number of neutrons, or equivalently the total of protons and neutrons (mass number) determines the isotope of that element. Some isotopes (unstable isotopes or radioactive isotopes) do not last long, e.g., undergo beta decay frequently enough that their half life is short. Stable isotopes are those that last a long time, and are ultimately more common after the unstable ones disappear. The ratio of the amount of an unstable isotope with its stable result can be used to determine ages of material.

A typical notation uses the element's symbol with a "left-side superscript" (i.e., superscript preceding the symbol) to indicate the mass number and (optionally, for clarity) a "left-side subscript" to indicate the atomic number. This notation is used, for example, in descriptions of nuclear reactions (e.g., nucleosynthesis).

Example: notation of the common stable isotope of helium (two protons and two neutrons):

4
 He
2

(physics)
Further reading:
http://en.wikipedia.org/wiki/Isotope

Referenced by pages:
abundances
Advanced Composition Explorer (ACE)
alpha capture
Avogadro's number (NA)
Big Bang nucleosynthesis (BBN)
beta decay
Bose-Einstein statistics
calcium (Ca)
carbon (C)
methane (CH4)
carbon monoxide (CO)
dalton (Da)
deuterium (D)
element
fractionation
fractionation factor
fusion
hydrogen cyanide (HCN)
helium (He)
International Cometary Explorer (ICE)
iron (Fe)
potassium/thorium ratio (K/Th ratio)
lithium (Li)
lanthanide (Ln)
magnesium (Mg)
mole (mol)
Moon formation
neon (Ne)
neutronization
nickel (Ni)
nitrogen (N)
oxygen (O)
proton-proton chain
presolar grain
radioactive dating
radioactive decay
radioactive heating
Rosetta
r-process
silicon (Si)
superluminous supernova (SLSN)
supernova light curve (SN light curve)
solar neutrino unit (SNU)
sodium (Na)
Solar and Heliospheric Observatory (SOHO)
spectral line designation
s-process
sulfur (S)
technetium star
valley of beta stability

Index