James Chadwick

James Chadwick (1891–1974) was a British physicist who discovered the neutron in 1932 and received the 1935 Nobel Prize in Physics.

Ernest Rutherford: Ernest Rutherford was a physicist who established the nuclear model of the atom and predicted a neutral nuclear particle. Rutherford’s earlier prediction of a neutral particle helped frame Chadwick’s search.
Beryllium: Beryllium is a chemical element with atomic number 4, notable for its low density and use in neutron-producing reactions. Alpha particles striking beryllium generated the penetrating radiation Chadwick investigated.
Neutron: A neutron is an electrically neutral subatomic particle found in atomic nuclei, with mass close to that of a proton. This is the particle Chadwick identified through recoil measurements in 1932.
Nuclear fission: Nuclear fission is the splitting of a heavy atomic nucleus into lighter nuclei, usually releasing neutrons and energy. Neutrons later made it possible to induce and sustain fission in heavy nuclei.
Proton–electron model of the nucleus: The proton–electron model proposed that atomic nuclei contained protons and embedded electrons to account for nuclear charge and mass. The discovery of the neutron displaced this model by explaining nuclear mass without nuclear electrons.
Hans Geiger: Hans Geiger was a German physicist who developed particle-detection instruments and studied radioactivity. Chadwick worked with Geiger at Manchester before pursuing the neutron.
Alpha particle: An alpha particle is a helium-4 nucleus containing two protons and two neutrons. Polonium alpha particles bombarded beryllium in Chadwick’s decisive experiments.
Neutron discovery: The neutron discovery was James Chadwick’s 1932 demonstration that penetrating radiation from beryllium consisted of neutral, massive particles. Chadwick’s paper connected beryllium radiation to the particle now called the neutron.
Nuclear reactor: A nuclear reactor is a system that sustains controlled nuclear fission to produce heat or neutron flux. Reactor operation depends on the neutron chain reactions Chadwick’s discovery made accessible.
Atomic nucleus: An atomic nucleus is the compact, positively charged center of an atom, containing protons and usually neutrons. Chadwick’s result established neutrons as a constituent of the nucleus.

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