 procedures results in the use of proton irradiations to evaluate both the TID and displacement damage response of a device. Recall from the discussion in section IVA, that "a rad is a rad" is a reasonably good assumption for proton energies above about 40 MeV, and it is therefore straightforward to calculate the proton induced TID. If concurrent TID effects are significant, then it is important to design the proton test with appropriate controls on the bias, measurement timing, etc. as described in IV-74 standard TID test methods such as MIL-STD-883, Method 1019. In such cases, there is always the possibility that the failure mechanism (TID versus displacement damage induced) depends on the ionizing dose rate employed in the test. Obviously, this is a concern since typical space dose rates are many orders of magnitude lower than those employed in laboratory proton measurements. Although it is possible to perform lengthy low dose rate testing at a Co-60 source, such testing is not feasible at a proton facility. In some cases, the relative importance of TID versus displacement damage dose may not be well characterized for a particular device. For example, the susceptibility of linear bipolar ICs to displacement damage and TID varies over a wide range because of significant variations in device design and processing techniques [Gaut83, John87, Rax97, Rax98]. A recent study of modern bipolar technology provides general guidelines to help identify cases where displacement damage is most important [Rax98], but sometimes this is best determined by comparing test results for both proton and Co- 60 exposures. Comparisons are made either by plotting the device degradation as a function of equivalent TID or displacement damage dose. Note that it is generally not possible to separate out the relative importance of TID versus displacement damage dose by comparing exposures at different proton energies. This is because both effects exhibit a qualitatively similar energy dependence as illustrated in figure 5. As will be discus