This spectrum generator is based upon the following article:
Boone JM, Seibert JA. "An accurate method for computer-generating tungsten anode x-ray spectra from 30 to 140 kV." Med Phys. 1997 Nov;24(11):1661-70.
This article (and the authors' original accompanying c code) has been invaluable. Initially, I rewrote the code for my own purposes in Matlab. So many people have asked me for spectra of one kind or another since then, though, that I decided to rewrite it in php so that people can get their spectra off the web. The purpose of this site is to educate residents and graduate students who want to learn what different spectra look like. I believe I have converted it correctly, but use at your own risk. You should read the above article and understand what you are getting if you plan to use these spectra for anything other than your own enjoyment. Also, if you use them for anything scientific, please cite the Boone article and verify the calculations on your own.
I also have an accompanying mammography spectrum generator.