5] for thermal SiO2 and suprasil glass in pulsed irradiation mode, [Boes-76] with 13 MeV electrons at 80K, [Peas-85] studied thick oxide under very low fields used in bipolar emitter-base spacers. A representation can be found in data recalled on fig. 12. Brown and Dozier made thorough studies of dependence versus the energy of photons and the structure of the ionizing tracks ([Dozi-81], [Brow-81], [Oldh-81/83/85]). [Oldh-82, [Oldh-84] and [Ausm-86] presented a refined analytical or numerical model taking into account the track density. A very simple model helps to picture the reasoning [Brow-81]. First, it is assumed that the cloud of holes and the cloud of electrons are swept apart in time t by an applied field. Second, it is assumed that while the electron and the hole clouds overlap, electron-hole recombination takes place following bimolecular kinetics, i.e. (14) dR where is a recombination coefficient and R is the electron (and the hole) density at time III-18 t. This equation can be integrated simply: with =d/uE is the time needed for columns separation, and u the (ambipolar) mobility. This leads to the simplest formula for the non-recombination or yield function: (16) Y(E)=R with Ec a critical field defined by = This simple calculation of "columnar" recombination is not always adequate because it supposes sufficiently dense tracks ([Oldh-84] showed it is valid for 107 electrons and holes generated per cm of track, i.e. for protons below 3 MeV, and electrons below 3 keV). Otherwise, a better model would be the "geminate" recombination, based on similar physics but where carriers are more dilute SO that they recombine as isolated pairs [Ausm- 86]. It leads anyway to similar conclusions. On fig. 13, the yield dependence is presented versus energy of particles, that is to say, track density. One notes the low yield for heavy particles and the influence of the electrical field Eox. For Co-60 and 10 keV X-rays, several updates were made in the late 80's and in the 90's, and precise comparison have been made ([B