Thanks for all the replies. I am impressed by the resources that RADSAFE taps into. A friend queried me for the info, and I was surprised that what I thought would be the obvious literature sources did not have the info. Thanks again. P.S. One forwarded reply went to RADSAFE by accident. Two buttons on the screen are too close together! Sorry. A little risk adds spice to life. slaback@MICF.NIST.gov