sed in section 3.3.5, optocouplers may also be subject to both TID and displacement damage effects [John96, Reed98]. DC-DC converter modules also may fail from either displacement damage or TID degradation, depending on whether the unit uses an optocoupler for isolation. Since CCDs are MOS devices, they are also subject to TID degradation. Although the performance of many CCD devices is limited by displacement damage, those from some manufacturers fail by TID induced threshold shifts in output circuitry. In many cases, it is useful to monitor the device properties after proton irradiation to look for substantial recovery which can be the signature of a device that has failed to function as a result of TID exposure at laboratory dose rates. (This practice can prevent the unnecessary disqualification for a device for space use. Note that this practice is consistent with the Method 1019 standard [Sext92] used for Co-60 tests. This procedure permits a room temperature anneal as a surrogate for a low dose rate test, as long as the device does not fail functionally.) Once again, the comparison of proton and Co-60 test results can help to sort out failure mechanisms. In the case of multi-component modules, one must always consider the possibility of both TID and displacement effects. For example, modules containing photonic devices expected to degrade via displacement damage mechanisms may also contain passive elements (e.g., lenses) that degrade from TID effects. Recently, the response of an InGaAsP laser module to protons was found to be dominated by darkening in a graded index (GRIN) lens, even though the laser itself was quite hard to displacement damage [Mars92]. (This behavior was confirmed through the use of additional Co-60 testing.) Given the wide range of hardness in lens materials, it can be useful to perform a cheaper Co-60 screening test of such modules before proton testing. IV-75 Proton test energies should be selected based on the particular application, as described earlier, but it is always important t