After I finished my Geiger Counters I wasn't happy enough to know that there is ionizing radiation, but also where it comes from. And for that a Gamma Spectrometer is needed.
It consists of a hand piece and a amplifier + converter and the power supply. The hand piece is in my case a Sodium Iodine crystal, doped with Thallium, NaI(TL). It converts the radiation into light pulses, which then a photo multiplier tube can see and amplify. Those current pulses then get converted into voltage pulses, amplified, conditioned and put into a sound card build into the device to be digitized and send to the PC for display. The sound card should be a rather good one, or better said one with low noise and high mic sample frequency. I found that the Soundblaster Play 3! works, but I also bought a couple of cheap ones to test. They all are sub 5$.
The power supply is a CCFL inverter where I regulate the input voltage. It works with 5V which come from the USB port, -5V from a ICL7660 and -1kV. All in all the whole spectrometer needs about 5V at 110mA.
For software I use the freeware Thereminio.
On the x-axis is the energy in keV and on the y-axis the frequency of a pulse at a particular energy. The spectrum that forms, tells whats inside a radioactive mineral for example.
The spectrometer in the square aluminium box was revision one. After revision two and three came, it got dismantled.
The one in the black case is revision two, and the last one is revision three, with on-board high pass filter, variable gain of the amplifier, on of switch, better filtering of the supply lines, added SMB connectors for the input and output signals and a better layout in general.
Some of those things were already implemented in Rev 2.
You also can see a hand-piece and the parts that go in it.
Thorium 232 (Th232) Spectrum. I measured a lamp mantle you use in gas lamps to get a brighter flame.
Radium 226 (Ra226) Spectrum. This is from two watches with Radium digits that light up in the dark.
The spectrum of uranium oxide or Pitch-blend.
You can see the Radium and Uranium peaks clearly.