ive defects. For example TRIM is often executed assuming a displacement energy threshold of 25 eV, which is considerably higher than the actual value. This practice helps to account for the efficiency of the initial recombination of the vacancy-interstitial pairs. In other Monte Carlo codes such as MARLOWE, one also has the option to define a radius around each collision point for which all the vacancy-interstitial pairs recombine. In essence, all current NIEL calculations must be scaled to fit the experimental damage factors, unless damage factor ratios are compared. As we shall see, it is the calculation of the energy dependence that is relevant, not the absolute values of NIEL. 2.3.1 The Correlation of NIEL to Device Behavior Device degradation in a radiation environment is often characterized by defining a damage constant, or a damage factor. Damage constants describe the change in basic material parameters such as minority carrier lifetime or diffusion lengths, produced by a given fluence of protons of a specific energy. (Fluence is defined as the number of incident particles per unit target area, and has units of Damage factors are similar except they characterize the observed radiation induced degradation of device or system parameters that may not be readily reduced to basic material parameters because a detailed device model is not available. IV-61 The following well known equation describes the degradation in minority carrier devices that results from the reduction in the diffusion length that accompanies the introduction of radiation induced defect recombination centers: 1/L2=1/Lo2 The initial and post-radiation diffusion length is given by L0 and L, respectively, K is the damage constant, and is the proton fluence. (Sometimes this equation appears terms of the minority carrier lifetime, T, using the relation, L = (Dt)O.5 where D is the diffusion coefficient.) Usually the satellite designer or test engineer is interested in a particular device parameter, and defines a relevant damage factor. In the cas