It is actually pretty small (at least the one we had for the lab classes), and you do not need much to build it (although I didn't build it myself).
It was a round table with detectors that could rotate around its circumference. Sources were put in the middle of the table, hidden (at least for the students). By rotating the detectors, they were supposed to localize precisely the sources.
Nice. So many ways we can educate the students about the basic science principles...