Shielding Thickness

For single event effect calculations, it is important to shield out low-energy particles which would never be encountered in a realistic situation. A nominal shielding thickness of 100 mils is therefore recommended for general comparison purposes. This value is set as a default on the TRANS input page. Of course, you may overwrite this default with a different value.

Reasonable estimates of SEU rates can generally be obtained with a single average or median shielding thickness during solar-quiet times. However, using a nominal shielding thickness (say, 100 mils or 1 g/cm2) in cases where the actual shielding is much thicker can lead to significant overestimates in the radiation environment.

In solar particle ("flare") environments , using an average or nominal shielding thickness is almost never adequate for reliable SEU rate calculations. Instead, careful treatment of the shielding is especially important, since solar spectra generally fall steeply with increasing energy. In these cases, using only a single shielding thickness can easily lead to factor-of-ten errors in the predicted SEU rate. For solar particle environments, SEU calculations should be carried out using a realistic distribution of shielding thicknesses.

For more information on the effects of shielding distributions on solar particle SEU rates, please see:

• E.C. Smith, "Effects of Realistic Satellite Shielding on SEE Rates", IEEE Trans. Nucl. Sci. NS-41, 2396 (1994).
• A.J. Tylka, W.F. Dietrich, P.R. Boberg, E.C. Smith, and J.H. Adams, Jr., "Single Event Upsets Caused by Solar Energetic Heavy Ions", IEEE Trans. Nucl. Sci.,NS-43, 2758 (1996).

For more information on thick-shielding effects, please see:

• C.S. Dyer, C.J. Watson, C.L. Peerless, A.J. Sims, and J. Barth, "Measurements of the Radiation Environment from CREDO-II on STRV & APEX", IEEE Trans. Nucl. Sci., NS-43, 2751 (1996).