tions) after incremental exposures at a given proton energy. Figure 6 shows the measured damage factors for protons, deuterons and helium ions normalized to the 1 MeV-equivalent (Si) neutron damage factors as a function of ion energy for a variety of Si bipolar transistors. (We will discuss the meaning of MeV equivalence in a later section, and neutron damage equivalence is explored in [Luer87]. For the present purposes we note that by comparing ratios of measured damage factor to IV-62 the calculated NIEL ratios, no scaling parameter is needed to match data with theory.) The importance of this result is the proportionality between the measured damage factors and calculated NIEL that provides the basis of the on-orbit predictions of device degradation produced by displacements. 2N2222A 2N2907A 2N3055 2N6678 2N6547 Helium lons Deuterons Protons DATA POINTS ENERGY (MeV) Figure 6 The transistor damage factor ratios for a variety of particles with fission neutrons are shown together with the corresponding calculations of the NIEL ratios. Note that both ordinates are identical (with no fitted parameters), which indicates a direct proportionality between NIEL and the damage factors over a wide energy range. After [Summ87]. Research performed in the last dozen years has shown that, to first order, the linear relationship between the device degradation from particle-induced displacement damage and NIEL holds for a variety of electrical parameters, incident particles, and device materials [Summ87, Peas87, Dale88, Mars89a, Walt91, Mars92, Ohya96, etc.]. This is a surprising result when we consider that NIEL calculations describe the energy deposited into the formation of Frenkel pairs (over 90% of which recombine), and do not consider the process by which the stable electrically active defects are formed. Since NIEL is a direct measure of the initial number of vacancy-interstitial pairs created, the implications of the NIEL correlation with device degradation are that: (1) the percentage of initial vacancy-interstitial pai