A number of documents have been produced discussing potential radiation effects in some detail. These are listed at the bottom of the page. A brief discussion follows on the key issues.

The orbit for EIS is a sun synchronous orbit (i.e over the poles) at a height of 600 km. Each orbit will take 90 minutes. The overall radiation dose likely to be encountered was estimated using the ESA SPENVIS program. At most, the total dose is expected to be under 10 krad, but should be much less once appropriate shielding is used. Most of the dose will occur during passage through the South Atlantic Anomaly, although some may occur during passage through the poles.

The main effects of radiation on the EIS CCDs are as follows:

• flat band voltage shifts - the effect of flat band voltage shifts can be minimised by allowing key voltages to be varied in flight. On EIS, we will be able to alter Vog (the output gate) Vss (the substrate) and Vod (the output drain). The potential flat band shift per krad for the 42 series CCDs can be estimated with some confidence and it is unlikely we will need to increase the voltages during flight.
• displacement damage in the  silicon substrate. The displacement damage is caused by protons and will lead to the formation of traps within the bulk depleted area of the CCD. During the charge transfer process, some charge may be trapped, lowering the Charge Transfer Efficiency (CTE) and reducing the image content. Potentially, a large loss in CTE could degrade the spectral images quite significantly. Displacement damage itself can really only be minimised by ensuring there is sufficient shielding around the CCD (heating the CCD up to large temperatures (say 150 degrees C) could improve matters, but could possibly make things worse and so will not be attempted in this programme). The effects of displacement damage can be reduced by cooling the CCD as the time constant of the traps is highly temperature dependent.

The following discussion papers should prove useful:

The potential degradation of spectral resolution in Solar-b EIS CCDs: (pdf file) The effect of large amounts of charge transfer
inefficiency (CTI) in the EIS CCDs will be to degrade the spectral line profile. This note attempts to quantify what the
potential loss of spectral resolution could be given a range of operating temperatures (and hence CTI values).

Initial CCD temperature investigations: A discussion of the potential temperature requirements for EIS including dark
signal and charge transfer inefficiency only in pdf currently

Initial consideration of the EIS radiation environment: A discussion on the effect of radiation on the EIS CCDs followed
by a trawl through the literature provide a first estimate of the sort of problems we may encounter. Only available in pdf.

Radiation shielding investigations using SPENVIS: calculations (using the ESA programme SPENVIS) of the likely radiation
dose encountered by the EIS CCDs. This information is then used to update the predicted radiated effects and estimate the
required shielding parameters. Also available in pdf.

The previous calculations are extended by including sectoring effects using a likely shielding design.