HPGe Gamma Ray Spectroscopy Education

Author: Tim

Tim has been teaching a course on HPGe based gamma spectroscopy for over ten years now. These are excerpts from his lectures to guide folks through the overall HPGe system basics.

Outline of topics this instruction will cover.

An un-shielded HPGe with “vertical dip-stick” sitting in liquid nitrogen reservoir within a 30 liter dewar.

Cross section of the above system.

Right-angle horizontal looking “dip-stick” exploded view.

Frost building up from detector freshly pulled out of liquid nitrogen reservoir.

Block diagram of electronic’s setup for spectroscopy system.

Amplifier chain up to the point of entering the MCA.

The NIM crate, with detector’s HV bias supply and spectroscopy amplifier, USB based MCA, and data acquisition laptop.

Collected spectrum of sample with known lines.

Linear fit to scatter plot of gamma energy vs MCA channel.

“Unknown” sample, a rock collected from Petaca NM.

“Unknown’s” spectra – which the gamma ray catalog identifies as thorium ore.

This is a 1-hour acquisition without any shielding around the detector. Many lines are seen, demonstrating our radioactive world.

Here the detector is almost entirely encapsulated in a shield, but left with the lid open. Again a 1 hour count.

Here the detector is almost entirely encapsulated in a shield, but left with the lid open. Again a 1 hour count.

Finally, a 1 hour count with the fully shielded detector.

Finally, a 1 hour count with the fully shielded detector.

Compilation of the three spectra.

This is a demonstration of a sequence of 5 minute counts, following the centroid of energy peak immediately after turning on the NIM crate, hence spectroscopy amplifier, bias supply, etc. Also plotted is the same data 24 hours later after the electronics have thermally stabilized.