Atomic Rockets says 5% of the energy comes out as neutrons for D-3He fusion, as opposed to 79% for D-T fusion: http://www.projectrho.com/public_html/rocket/fus

Atomic Rockets says 5% of the energy comes out as neutrons for D-3He fusion, as opposed to 79% for D-T fusion: http://www.projectrho.com/public_html/rocket/fusionfuel.php#id--Fusion_Reactions http://www.projectrho.com/public_html/rocket/fusionfuel.php#... No source given, but this is usually well-researched.