Sy Teller light from X-rays is mck mre intense aad occurs sch mearer rhe burst point. Further discussion of the Teller ligtt pulse is preserred in a later section. 11.2.% Thernal Radiation and Teaz Fireball Dewelopment At 250,000 feet altitude, it is estimated that about two-thirds of the a large volume because of low ambient air density. Y-ray energy is rapidly transferred to energetic photoelectrons and auger electrons which deposit their energy locally by further ionization aaj excitation. The approximate energy deposition in electron wolts per air atom is illustrated in Fig. 11.1 wersus radius. The omber of ion pairs produced per atom by energetic elec- trons can be read directly from the graph as ¢/32, since it requires 32 ev to forms an ion pair in air. Thus, for example, all air atoms are at least singly ionized within a radius of about GO) feer. Esdistion emitted by excited air depends on the state of the air imedistely following initial deposition. Ex- cept for prompt Teller eaission already wentioned, the most important processe which ow occur are those which bring about a statistical equilibrium! The general characteristic of the air immediately after deposition % the bomb's energy is the presence of an excess of mlecules, seutral and ionized, for the energy content of the sir. an excess of electrons. In the closer region there is, in addition In the outer region, dissociation of neutral molecule by collisions is slow (approximately 1 to 100 msec). Thus, in the beginning, at least, radiation from the outer fireball is predocinantly from molecules. Closer to the boob, where there is substantial fonization, molecules and electrons disappear together by a cocbination of two nouradiative reactions: Np + @ = 2N and No +N” 2 yy +3. The first is dissociative recombination; the second is charge exchange. Both of these are sufficiently fast that equilibrium is attained in about l psec, and as a result dissociation of all mlecules occurs, fonized air atoms and electrons. leaving A sisple argiment shows that this will be the case out to the radius for which € « 10 ev/atow (approxisarely), which occurs at about 15,000 feet. The principal source of optical) radiation from the 33: Sa N region in Fig. 11.1. This woluve is referred to as the ionized core