pset map for two adjacent SRAM cells [60]. For this SRAM, diffusion of charge from ion strikes between cells is responsible for MBU. Particle Energy Effects Heavy-ion tests at accelerator facilities are frequently performed to study mechanisms of SEU, estimate on-orbit error rates, and qualify parts for use in space-based systems. In most facilities used for such SEU testing, the energy of the particles is on the order of a few (1-10) MeV per nucleon (or equivalently, MeV/amu). However, in the actual space environment, the energy of particles reaches hundreds of GeV/amu, with a peak flux at a few hundred MeV/amu [1]. Figure 3.15 shows the galactic cosmic ray energy spectrum for Fe ions in a geostationary orbit at solar minimum conditions behind 100 mil of Al shielding [118]. The range of ion energies available at typical low-energy accelerators such as the Tandem Van de Graaff at Brookhaven National Laboratory (BNL) is marked by the light gray band. Higher energy ions (10-100 MeV/amu) are available at a few facilities, for example the GANIL cyclotron in France and the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The range of ions available at these facilities is marked by the darker gray band in Figure 3.15. Note that even the "high" energy facilities produce ions with energies well below the maximum encountered in space. The linear energy transfer (LET) of the Fe ions as a function of energy is denoted in Figure 3.15 by the shading of the symbols. The usual low-energy test facilities produce ions with energies where they have maximum LET (greater than 20 MeV-cm2/mg for the case of Fe) but lower fluences in space. Ions with intermediate energies (10-100 MeV/amu) are much more abundant and can still possess large enough LETs (between 5 and 20 MeV- cm²/mg for Fe) to be of concern, especially for sensitive commercial technologies. Note also that spacecraft shielding becomes ineffective with increased ion energy [1]. Extremely high-energy ions usually have low LETs (less than 0.2