Uploaded September 2026 | Updated September 2026, 1 week ago

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Chadwick’s discovery of the neutron explained isotopes and atomic mass. Faced with utter confusion over 2 different masses of neon, what did James Chadwick do? He discovered a new particle: The Neutron. With the help of JJ Thomson and Francis Aston's early mass spectrometry (mass spectrograph), Chadwick performed groundbreaking radioactive experiments to discover the neutron.

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0:00 Early Mass Spec (Mass Spectrograph) Experiments
2:10 Puzzle of Neon's 2 Masses
2:47 What We Already Knew About Atomic Structure
3:18 Mysterious Gamma Radiation
3:38 Alpha and Beta Radiation
4:25 Experimental Setup: Polonium Decomposition
4:58 Beryllium Reaction
5:30 NOT Gamma Radiation: Balancing Beryllium Equation
6:25 Paraffin Wax and Mystery Radiation Reaction
7:10 Laws of Conservation of Energy & Momentum
7:49 Neon's 2 Masses Explained by the Neutron

Citations:
theanalyticalscientist.com/issues/2013/articles/sep/the-origins-of-mass-spectrometry
openstax.org/books/chemistry-2e/pages/2-2-evolution-of-atomic-theory
Paula Yurkanis Bruice, "Organic Chemistry" 8th ed
openstax.org/details/books/organic-chemistry
openstax.org/details/books/chemistry-2e

Music: youtu.be/lL6AsbG07xY

Images:
By Not Mentioned - First World War.com, Public Domain, commons.wikimedia.org/w/index.php?curid=2969861
By Unknown author - nobelprize.org/nobel_prizes/chemistry/laureates/1922/aston.html, Public Domain, commons.wikimedia.org/w/index.php?curid=18253663
By Francis William Aston - "Positive Ray Parabolas". Isotopes. London, England: Edward Arnold Publishers Ltd, 1922. Digital file made available by Science History Institute, at digital.sciencehistory.org/works/79407z32j, Public Domain, commons.wikimedia.org/w/index.php?curid=2976526
By The original uploader was Den fjättrade ankan at Swedish Wikipedia. - Källa:Dmitrij Ivanovitj Mendelejev (1834 - 1907). Originally from sv.wikipedia; description page is/was here., Public Domain, commons.wikimedia.org/w/index.php?curid=1574857
James Chadwick Photo, commons.wikimedia.org/wiki/File:Groves_and_Chadwick_830308.tif: Unless otherwise indicated, this information has been authored by an employee or employees of the Los Alamos National Security, LLC (LANS), operator of the Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396 with the U.S. Department of Energy. The U.S. Government has rights to use, reproduce, and distribute this information. The public may copy and use this information without charge, provided that this Notice and any statement of authorship are reproduced on all copies. Neither the Government nor LANS makes any warranty, express or implied, or assumes any liability or responsibility for the use of this information.
Periodic Table used with permission from sciencenotes.org/printable-periodic-table