Effects of X-ray on EPLD Technology

Does anyone have any evidence on the effects or limitations of x-rays on electronic equipment, EPLD's in particular?

I am involved in an x-ray test and i'm trying to pull together some limits on the exposure of x-rays on electronic equipment. There is a lot of hear say online and i've not been able to find any actual numerical values on the maximum exposure you can subject EPLDs to before you damage them or effect their function.

Can ayone point to any reports or does anyoen know if Altera have stated a maximum radiation exposure limit on their products? Or if anyone has already done some testing I would be very interested in the results.

Thanks.