First of all, I'm not the one doing this experiment. I've just finished my first year in college and I'm sort of just helping all the upper-level with their research and whatnot. So my knowledge is very limited. With that being said, one of those student is doing X-ray Fluorescence. He was just wondering if there is an "optimal" angle to which the x-ray could be pointed to get the best results. http://upload.wikimedia.org/wikipedia/en/thumb/2/28/Dmedxrfschematic.jpg/800px-Dmedxrfschematic.jpg [Broken] Here is a pic from wiki which sort of shows the basic set up. He was thinking maybe a 120 degree angle would be good or maybe 90 degrees (Like in the picture). Bear in mind that he didn't really ask me to do research or anything. I just wanted to find out so he didn't have to take the time to figure it out by trial and error. Please forgive any terms I may have messed up on. If you need any more information just ask and I'll try to find out. Thanks in advance.