Radiation damage in mixed radiation fields

Degradation data on device, circuit, or system are required in order to harden against mixed radiation fluences. These fields can usually not be adequately produced by simulation machines. The functional dependence of a degradation parameter with fluence for each type of radiation is first established. Using the same sample device, an equivalence between different types of radiation is next established. This then enables a calculation of the degradation for the mixed radiation fluences. Neutron degradation is a special case since the method of neutron dosimetry (n/cm2 per unit energy) reveals an energy dependence of neutron degradation. If, for example, gamma ray degradation has an energy dependence this is masked by the present dosimetry (rads Si). The change of drain current in a JFET in a mixed neutron and gamma field is used as an example of the present technique. The degradation functional dependence of each of four simulation neutron spectra is first established. The neutron spectra is then synthesized with the four spectra. Thus the equivalence of the neutron spectrum in terms of a simulation machine spectrum is obtained. Also the equivalence between the gamma field and the simulation machine neutron spectrum is obtained. These are now combined and the effect of the mixed neutron gamma field is expressed in an equivalent fluence of simulation machine neutrons. Errors and limitations of the method are discussed