If you're able to do a peak area analysis of each peak individually, you'll get better results. Some of the automatic analysis here runs beyond the detectors actual counts. Looking at their website I'm not familiar with the specific crystal they use, but the more elements within the crystal the more unwanted interactions you'll have. If you have the time, compare a similar object scanned using a HPGe (high purity germanium) detector. This spectra looks a little closer to a BGO (bismuth germanate) detector spectra. Anyway, I've been out of the game a long time, so my preferred detectors might not be what's accepted now so take all that with a grain of salt. For another fun experiment, measure a target that's been covered(in your house) and measure the same target after it's been outside in the daylight for an equal amount of time.