CNO Cycle, Sun, H. Bethe
Discovery of the Muon particle
O. Hahn and F. Strassman process of nuclear fission in uranium and thorium
1938 — Paul Dirac suggests the large numbers hypothesis, that the gravitational constant may be small because it is decreasing slowly with time
24 February 1938 discovery of 2665 Schrutka and 4181 Kivi
17 November 1938 discovery of 3008 Nojiri
15 April 1938 Death of Anders Severin Donner in Helsinki, Finland,
1938 Death of Francis G Pease
1938 Death of Edward Charles Pickering
1938 Birth of David Nygren
Physics to Enrico Fermi for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons.
Chemistry: to Richard Kuhn "for his work on carotenoids and vitamins"
Physiology or Medicine to Corneille Jean François Heymans "for the discovery of the role played by the sinus and aortic mechanisms in the regulation of respiration"