These devices usually sell for about $10,000. I bet I can build one for much, much cheaper. As a chemist, the idea of being able to instantly determine the elemental content of almost any material, wherever I am, not having to be in the lab, gives me a massive nerdgasm. I would use this thing way too much... which brings me to the next point: safety. As X-rays are hazardous to life, making sure such a device is safe is extremely important. Lead shielding will be used and I'll try to eliminate all x-ray exposure and minimize beam intensity. Testing of the device will need to be done using a very controlled setup.
There was a company that made XRFs that relied on the sticky tape type x-ray generation. The cartridge had to be replaced periodically though and they were not cheap.
I am incredibly interested in this project as I have been researching mineralogy and EMF extensively of late. If there is any assistance that I can offer please let me know.
Many of the parts required are easily available from Amptek and Newton Scientific if you have the funds. Still considerably cheaper than finished commercial products. Here is a kit from Amptek that can be built. http://amptek.com/products/complete-xrf-experimenters-kit/
I worked on XRFs a lot last year. Not handheld ones though, but benchtops and some really really big ones. It will be cool to see where this project goes.
I have assembled all the components I think are needed to do a benchtop DIY XRF. I would like to join this project and see if we can accomplish it.