A condition for the release of energy from a thermonuclear reactor first laid down by John David Lawson (1923–2008) in 1957. It is usually stated as the minimum value for the product of the density (n_G) of the fusion-fuel particles and the containment time (τ‎) for energy breakeven, i.e. it is a measure of the density of the reacting particles required and the time for which they need to react in order to produce more energy than was used in raising the temperature of the reacting particles to the ignition temperature. For a 50:50 mixture of deuterium and tritium at the ignition temperature, the value of n_Gτ‎ is between 10¹⁴ and 10¹⁵ cm⁻³ s.