First positron source in Phoenix
The first positron source in Phoenix is unknown.
The field of positron astronomy is the result of observations and theories about positron sources detected in the sky above.
The first astronomical positron source discovered may have been the Sun.
But, positrons from the Sun are intermingled with other radiation so that the Sun may appear as other than a primary source for positrons.
The early use of sounding rockets and balloons to carry positron detectors high enough may have detected positrons from the Sun as early as the 1940s.
This is a lesson in map reading, coordinate matching, and researching. It is also a research project in the history of positron astronomy looking for the first astronomical positron source discovered in the constellation of Phoenix.
Nearly all the background you need to participate and learn by doing you've probably already been introduced to at a secondary level and perhaps even a primary education level.
Some of the material and information is at the college or university level, and as you progress in finding positron sources, you'll run into concepts and experimental tests that are actual research.