Margaret, Nuclear Chicago has too many years out of bussines. In fact it was sold to Texas Nuclear long time ago and as far as I know Texas Nuclear already is out of bussines. We have a complete laboratory based on Nuclear Chicago, perhaps we can share some information. Hector R. Vega Universidad Autonoma de Zacatecas (MEXICO) e-mail: cren@campus.zac.itesm.mx hrvega@mers7.me.utexas.edu