Radiation-induced electrical insulator breakdown

A mechanism is determined for the induction of electrical breakdown in thick solid insulating material exposed to high-energy particles or photons. The authors have found a mechanism where common radiation levels, greater than on the order of 100 rad/h, will induce breakdown in insulators under typical high levels of applied electric field stress. In the experiments reported here, an attempt was made to determine if beam-induced discharges could couple with an applied (battery or power supply) electric stress and result in full insulator failure. Without applied voltages, the discharges were transient and the insulators recovered their properties within microseconds, even though the beam continued after the discharge. A model explaining the experimental results is developed. It is seen that peculiar combinations of geometry and radiation are required in order to produce radiation-initiated breakdown. The radiation must induce high fields over a small volume of the insulator so that the normal bias levels can invert the space-charge-induced fields through the rest of the dielectric. Also, before it quenches, the streamer must propagate fully through the insulator. These conditions can be used to encourage the occurrence of the breakdown, or one can choose geometries to avoid the problem