 MeV-cm2/mg for Fe) and therefore do not pose a serious SEU threat except for very sensitive devices. At a given LET, a high-energy cosmic ion track will have a much larger radius and much longer range than a low-energy accelerator ion track. This might lead to different charge- II-25 lon LET (MeV-cm2/mg) "High" Energy Energy Range Range (GANIL (BNL) & MSU) Energy (MeV/amu) Figure 3.15. Galactic cosmic ray iron spectrum vs. energy with LET denoted by symbol shading [118]. Ion energies available at typical accelerator facilities range from approximately 1-100 MeV/amu. collection properties, and hence, different SEU response. Recent SEU tests at high-energy accelerator facilities have indeed suggested a difference in IC response to particles with different energies. For example, differences between low- and high-energy ion tests have been seen to date in SEU thresholds and saturation cross-sections [119,120], single-event multiple-bit upset (MBU) occurrence [111,121,122], and unexplained inconsistencies in single-event burnout data [123]. Yet, in some cases, no appreciable difference has been observed between low- and high- energy heavy ion data [124-126]. The results that show differences are worrisome in that they raise concerns about the fidelity of accelerator-based tests for simulating the response of parts to the real high-energy ion environment found in space [127,128]. There are certainly cases where low-energy and high-energy ions have unambiguously given different test results. In these cases, however, it is the greatly increased range of high-energy ions that has led to differences rather than radial track structure effects. For example, in grazing angle irradiations, the greatly increased track-length of high-energy ions leads to multiple-bit upsets of many more cells along the track than would be seen with the shorter range of low-energy ions [111,121]. There may be other cases where the larger range of high-energy ions leads to different results, such as cases where the ions must pass through a great 