11.2.2 Teak Shot T Y expected to represent a aarked departure fram the phenomenology of a Sea-lewel burst. At this altitude, air density (a2, 3 1979) is such that X-rays are deposited fa a sphere of approximately 30,000 feet radius. Hydrodynamics are much less important than at sea level ani develop very late compared to the time for radiation cooling of the fireball. As a result, nearly two-thirds of the yield is radiated sway in a single thermal pulse of sbort duration (about 10 msec). Because of low ambient air density and relatively low temperature of the fireball, the heated air is quite transparent, so that direct obserwation of the inner portions of the fireball can be made. 11.2.3. Teller Light Teller light is well known in the case of sea-level burses® as the intense early light from the air surrounding the burst before formation of the fireball. collisions, it is generated by gamma radiatisc a>sorded in the air by CumpiosFast recoil electrons (a few hundred kew) rapidly transfer gamma energy to excited states of air molecules, giving rise to a characteristic emission spectrum in the visible frou Ny and ND: AC Teak altitude the air can be sisilsrly excited by photoelectrons produced by absorption of soft X-rays at relatively large distances froa burst point. Absorption of both gamma rays and X-rays can thus give rise to proupt emission from excited molecules, and both radiations are therefore considered . sources of Teller light. Because of the long collision time cf mlecules at 250,000 feet (about 1 psec), the Teller light phase of the explosion is greatly enhanced. Since the lifetice of an excited state is about 10% sec, wirtually all excited molecules radiate before the excitation is traasferred to kinetic energy by collisions. . Because of che long mean free path of gama rays at 250,000 feet, deposition of gamma energy is much less than that from X-radiatign ac burse altitude. At an altitude of about 100,000 feet, however, air density is such chat there is a broad region of substantial gamca-ray absorption. Thus, oost of the Teller light generated by gaauma radiation arises frow this lesser altitude.