Times to ignition in systems initiated by light

An infinite slab of an exothermic reactant has one face kept at ambient temperature whilst the other is subjected to a continuous flux of radiant energy. When reactant consumption can be ignored, a stationary temperature distribution is approached that can persist as long as conditions for criticality are not surpassed (δ≦δcr). When conditions are marginally supercritical, the temperature distribution eventually peels away. Times-to-ignition tign are shown to obey the rule tign∝(δ–δcr)–1/2 where δcr depends on the intensity of the illumination, and values for the proportionality constant are calculated.