[ben_w]

If you could somehow do that without the 140 gigacoulombs of charge exploding violently before you got close, approximately this: https://youtu.be/YtCTzbh4mNQ?t=16

If you don’t invoke space magic to prevent the positrons from exploding even before they annihilate anything, and they are confined into a 0.1m radius ball, the charge density energy overwhelms the annihilation energy and the ball of positrons explode with a yield of ~1e33 J, which — without exaggeration — looks more like this: https://youtu.be/KNjWpSglUOY