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helium (He)Type: Term
1. A gaseous element present in minute amounts in the atmosphere (0.000524% of dry volume); atomic no. 2, atomic wt. 4.002602; used as a diluent of medicinal gases; used as a diluent of oxygen principally in nonmedical applications, and in its liquid form as the coolant for super-conducting magnets (as in magnetic resonance imaging).