13a path taken by a particle of ionizing radiation in a cloud chamber, bubble chamber or photographic emulsiuon 5 letters: ??a?k (? quark)
17a mathematical quantity greater than any fixed assignable quantity represented by the symbol oo 8 letters; ??f?n?t? (?affintity)
8 down any of a group of complex phospholipids occuring in many plant and animal tissues especially egg yolk; used as a food emulsifier and stabilizer as additive E322 8 letters: ?e??????