The mass number is typically the number of particles in these objects, which were discovered in Ernest Rutherford's gold foil experiment.
"Halo" varieties of these objects deviate from the liquid-drop model, and "hyper" varieties contain at least one hyperon. "Magic numbers" predict islands of stability where these objects have long lifespans and deviate from the semi-empirical(*) mass formula's predicted binding energy. Gamma decay may occur when these objects are in an excited state. The mass number is typically the number of particles in these objects, which were discovered in Ernest Rutherford's gold foil experiment. For 10 points, identify this central region of an atom containing protons and neutrons.
"Halo" varieties of these objects deviate from the liquid-drop model, and "hyper" varieties contain at least one hyperon.
Atomic {Nuclei} [or the Atomic {Nucleus}, prompt on “{Atom}s”]