Radiation damage function analysis

Considerable efforts have been expended to measure radiation damage effects on materials justified by their impact upon nuclear design and operation. The experiments can be difficult to interpret. A large number of parameters including temperature, material variables, neutron spectrum, and fluence are entailed in the evaluation of radiation damage data. It is further complicated as each of these variables may change with time. The concept of a damage function relates radiation damage to the neutron spectrum forming the basis of conventional damage function analysis. The damage function description is related to the cross-section for damage at each neutron energy. This conventional formulation is unduly restrictive. A generalized damage function is postulated which includes not only neutron energy dependence, but also time dependence. Other important material variables as well as fluence are also considered to be explicit variables of the generalized damage function. Important implications of this generalized integral representation are discussed. To provide guidance and insight in this investigation, radiation dosimetry analysis is used as a fundamental analogue. It is shown that the generalized damage function is unique. Additional characteristics of generalized damage functions are determined by considering constraints imposed by physical requirements and conditions. For application it is necessary to reduce generalized radiation damage function analysis to simple models. Assumptions that can be invoked to provide these models are discussed including separation-of-variables and restriction to steady state irradiation conditions. Conventional damage function analysis follows directly from generalized damage function analysis upon the introduction of these simplified models