ensitive to displacement damage, it is often necessary to resort to the use of thick shields to minimize the radiation damage at the CCD location. As we will explore in section 3.1.2, displacement damage effects from secondary particles (mostly neutrons) produced in thick shielding can be significant, especially for high atomic number shields such as Ta. To calculate the effects of more than one particle type (such as secondary neutrons produced in shielding), the contribution for each particle is computed independently, as discussed earlier. The NIEL for neutrons in Si is described in [Dale91]. Figure 11 shows the results of equation 8 for the EEV imager in the 705 km, 97.4° polar orbit for four Al shield thicknesses, including the effects of secondary particle damage. The integral displacement damage dose and ACTE due to protons above a given energy are obtained by evaluating the integral from E to the highest proton energy. The intercepts show the effects of particles of all energies in terms of non-ionizing energy deposited per gram Si per year, or as the ACTE per year. We see that the relative gains from adding shield mass diminish as the shield gets thicker. Also, except for lightly shielded imagers, most of the damage results from protons over 10 MeV. These calculations are useful for determining the most relevant proton test energies for a particular shielding configuration. It can come as a surprise to discover that, in a heavily shielded application, half (or more) of the displacement damage dose is contributed by incident protons with energies in excess of 100 MeV. This is true despite the fact that lower energy protons produce more displacement damage, because the transported proton spectra are becoming much harder with increasing shield thickness. The spectral IV-72 hardness occurs because the lower energy incident particles have a higher LET and are therefore preferentially stopped in the shielding. 1.0x10 EEV CCD TRAPPED PROTONS 376X578 ARRAY SAGE ORBIT 0.8x10 CTE w/ Ti X-RAYS 705 km, 97.4° ALUMINU