Positrons are a remarkable kind of elementary particle, the antimatter counterpart of familiar electrons.  They were the first form of antimatter ever detected, and are a fine illustration of the powers of relativistic field theory to describe anti-particles.  On the side of applications, positrons are famous for their use in PET-scans (positron emission tomography), a form of medical diagnostics.  In the undergraduate lab, positrons are readily available from radioactive sources, and are easily and very selectively detected by relatively simple means.

The Immersion in ‘AntiMatter Matters’ includes everything that is needed for students to understand how positron-annihilation events can be convincingly and sensitively detected.  In an apparatus that fits easily on a small tabletop, and which requires only license-exempt radiation sources, students will have two gamma-ray detectors, plus all the electronics needed to process the detected gamma-ray events.

This experiment is made affordable via the use of new and compact gamma-ray detectors, based on CsI(Tl) scintillators and SiPM optical detectors.  The electronics package includes the 29-V power supplies for the two detectors, two channels of amplifier/discriminators for (single-channel) pulse-height analysis, a time-coincidence module to enable selective detection of simultaneous events, a three-channel gated counter, and a dual pulser module for calibration and set-up.  The Immersion will take users through a progression of pulse-detection methods that will illustrate the selective detection of the special character of two-gamma positron-annihilation events.

This equipment offers additional capabilities for other experiments, including gamma-attenuation studies, background radiation detection, active-target Compton scattering, gamma-gamma coincidence techniques, and even the photo-production of positrons.  All of it is understandable by newcomers to nuclear-detection techniques.

The equipment for AntiMatter Matters will be introduced in March, and available for Immersions 2026, and should be commercially available by September 2026 at a introductory price yet to be determined.  Equipment includes two gamma-ray detectors and their power supplies, a set of three radioactive sources, a full set of pulse-processing and counting equipment, a working table-top and the items for holding sources, detectors, shielding, etc.  The only additional item needed is a digital oscilloscope; a multichannel analyzer (MCA) might be used, but is not needed for the experiments in the Immersion. 

Hosts and Mentors:

Jonathan Reichert:  My first experience with magnetic resonance experiments came in the 1950’s as a graduate student at Washington University, when this was a brand-new tool for physicists.  Most of my forty-year research career was spent doing some type of magnetic resonance experiments.  At both CWRU and SUNY Buffalo, I developed and taught the advanced laboratory course.  I shared in the design and construction of both PS1-A & B and PS2-A, TeachSpin’s pulsed NMR apparatus.

David A. Van Baak (PhD, Harvard 1979) is Professor of Physics Emeritus of Calvin College, and since 2014 a Staff Scientist at TeachSpin, Inc.  His research interests have included r.f. and laser spectroscopy, and metrology and instrumentation in general.  During his Calvin College career, Van Baak spent over three decades working with advanced-lab curriculum and apparatus development.

Please note that the Jonathan F. Reichert Foundation has established a grant program to help purchase apparatus used in Laboratory Immersions. Limitations and exclusions apply, but generally speaking the Foundation may support up to 50% of the cost of the required equipment.