Atom to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as a whole; a charged atom is called an ion. Electrons have been known since the late 19th century, mostly thanks to J.J. Thomson; see history of subatomic physics for details. Protons have a positive charge and a mass 1,836 times that of the electron, at . The number of protons in an atom is called its atomic number. Ernest Rutherford (1919) observed that nitrogen under alpha-particle
Up An' Atom training and practice bombing missions and pumpkin bomb missions against industrial targets in Taira and Hamamatsu, Japan. Capt. Bob Lewis's crew B-9 flew it on a pumpkin bomb mission to Tokushima subsequent to the Hiroshima mission, and Lt.Col. James Hopkins and crew C-14 used it to attack Nagoya with a pumpkin bomb. "Up An' Atom" returned to the United States with the 509th CG in November 1945 to Roswell Army Airfield. From April to August 1946 it was assigned to the Operation Crossroads task force. In August 1949 it became part of the 97th Bomb Group at Biggs Air Force