rsc.org helium helium http://www.rsc.org/periodic-table/element/2/helium helium as alpha particles helium helium helium http://www.rsc.org/periodic-table/element/2/helium helium as alpha particles as alpha particles helium He helium rsc.org helium helium helium rsc.org rsc.org helium He helium rsc.org helium Source: Royal Society of Chemistry as alpha particles