Americium is a man made radioactive isotope, and is commonly found in smoke detectors. The source is an alpha emitter, and in the decay process it also kicks out a gamma at 59.6KeV. This is a typical gamma spectrum from Americium, as you can see, the tall peak at 59.6 KeV is very obvious and over powers everything else, it also has a gamma at 26.3KeV which is sometimes visible to the left of the tall peak. There are a whole bunch of other gamma rays from 241Am, but these are not easy to see with NaI detectors.
The following spectrum of 241Am, was submitted by Peter Daley, recorded with a GS-1100A and a 2" Alpha Spectra NaI detector. Excellent resolution and a very typical 241Am shape. Recognising isotopes by the shape of their spectra is an art and takes practice, which is why we are building this database of spectra.