The phrase "heavy atoms" refers to atoms that have a relatively large number of protons and neutrons in their nucleus compared to lighter atoms. Full definition
She had used the presence or substitution of heavy atoms to help define earlier structures, and she realized cobalt could play a similar role. (cen.xraycrystals.org)
But the researchers were unable to incorporate heavy atoms in these crystals. (lindau-nobel.org)
These stars are relatively more metals rich than outer - halo stars, with around three times more heavy atoms such as iron and calcium. (members.nova.org)