Radioactive materials are easy to detect with a Geiger counter, but cannot be identified with a Geiger counter. You need an isotope detector.
One of the most widely used isotope detectors is a Gamma Scintillation Spectrometer. In this video I explain how Gamma Spectrometers work. I also show you actual real-time capture of gamma spectra from several sources:
And Natural Uranium & progeny.
Please visit my website for a short explanation of the basics of radiation!
Spectrum Techniques (Where I get my sources and Spectrometry equipment)
GeigerCounters.com (Where I get my Geiger counters)