We maintain/operate a NaI detector for undergraduate use. I think it is a
wonderful tool and I use it for quite a few experiments.
One of the experiments is a study of Compton Scattering. With a NaI
detector (or other gamma detector) we see events in the primary peak that
occurred when the gamma deposited it's full energy in the NaI crystal. But
it is also possible for the gamma to Compton scatter and leave the crystal.
In this case it deposits a fraction of its energy in the detector. The
relativistic mechanics of this interaction dictates a minimum energy for the
scattered gamma which translates into a maximum energy deposited in the
crystal. Therefore there is a gap in the spectrum between the main peak and
the Compton-scattered events (which appear as background counts). The
high-energy side of this background is called the "Compton edge" and it
occurs right where Compton scattering calculations predict it should occur.
The handout I have written for this lab is available as an Adobe Acrobat PDF
file. In keeping with our policy of not attaching files to e-mails
submitted to the list, I am not attaching it. People wanting a copy can
e-mail me directly. Please do not request this through the list... request
it my direct e-mail address so I can simply hit my "reply" button.
We maintain a 2" NaI detector in a lead shield. It is made by Bicron, but
we bought it from "The Nucleus" which is no longer in business. The HV
power supply and amplifier were also purchased from The Nucleus as was the
ADC and software for the computer. The whole system cost us about $4000
(not including the computer).
Companies making nuclear sources and detectors for education keep changing
all the time. The Nucleus underwent changes something like Tennelec to
Ortec to Canberra to Oxford or something like that over the past 10 years.
It's been rough to find any continuity in a supplier. I think many of the
original "The Nucleus" people are still in business in Oak Ridge, TN under
the current name of Spectrum Techniques, Inc. Their website is:
Our system is similar to what you see if you go to their page on
Spectroscopy Systems then go to Spectroscopy Systems for PC. We have a
larger lead shield and our amplifier, power supply, ADC are separate pieces.
Now those pieces are all available on one board that goes into the PC. We
have operated our system for quite a few years. I think it is simply
wonderful... but my background is nuclear detectors, so I am biased.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817