Atom bombardment ejects what appeared to be hydrogen nuclei. By 1920 he had accepted that the hydrogen nucleus is a distinct particle within the atom and named it proton. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of the electron, or , the heaviest of the three constituent particles, but it can be reduced by the nuclear binding energy. Neutrons and protons (collectively known as nucleons) have comparable dimensions—on the order of —although the 'surface' of these particles is not sharply defined. The neutron was discovered in 1932 by the English physicist James Chadwick.
Up An' Atom Up An' Atom Up An' Atom was the name of a B-29 Superfortress (B-29-36-MO 44-27304, Victor number 88) configured during World War II in the Silverplate project to carry an atomic bomb. Assigned to the 393d Bomb Squadron, 509th Composite Group, it was built at the Glenn L. Martin Aircraft Plant at Omaha, Nebraska, accepted by the Army Air Forces on April 3, 1945, and flown to Wendover Army Air Field, Utah, by its assigned crew B-10 (Capt. George W. Marquardt, Aircraft Commander). It departed Wendover for North Field, Tinian on June 11 and arrived on June 17. It was