Na-22

Sodium-22 (Na-22) is indeed being investigated as an efficient generator of "cold positrons" for producing muons to catalyze fusion of deuterium. It's a positron-emitting radioactive isotope of sodium with a notably long half-life of 2.6019 years, undergoing positron emission to Ne-22. This makes Na-22 a subject of interest not only for potential applications in fusion energy but also for its use in positron annihilation spectroscopy, where it serves as a reliable positron source. The unique properties of Na-22, including its emission of positrons and monochromatic gamma radiation with an energy of 1274.5 keV, render it valuable for various scientific and medical applications, particularly in laboratories where it's utilized to create test objects and point sources for positron emission tomography​.