Biographical Memoirs Volume 81 (2002) / Chapter Skim
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John Alexander Simpson
John Alexander Simpson
Pages 318-339
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3~ o to .—~ a hi a UO o ~0 .
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scientists nonetheless. The upshot was that John Simpson became a founding member and first chairman of the Atomic Scientists of Chicago, formally founclecl August 7, 1945, the day after the United States dropped the atomic bomb on Hiroshima.
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320 B I O G RA P H I C A L EMOIRS Luce, publisher of Time and Life magazines, was sufficiently impressed with the thoughts and concerns of the Atomic Scientists of Chicago that he proviaca them with two full pages in the October 20, 1945, issue of Life to spell out the implications of the atomic bomb and possible rational courses of action in response to the implications. In 1945 Simpson joined the faculty of the University of Chicago as an instructor in the Physics Department.
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It was recognized, from the variation of the cosmic ray intensity with geomagnetic latitucle en cl from the east-west asymmetry of their arrival at the surface of Earth, that cosmic rays are mostly charger! particles, as distinct from energetic photons, with the majority of the particles positively charged.
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Tociay we know that the cosmic rays are created throughout the galaxy by such energetic phenomena as supernovae en cl that the cosmic rays in the large represent a tenuous relativistically hot gas, with dynamical pressure comparable to the magnetic fielcis en c! other gases in interstellar space and in the galactic halo.
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the potential of the neutrons en cl the lower energy cosmic ray particles for probing the causes of the time variations. That is to say, the strong time variation of the Tower energy cosmic rays is a thumbprint of whatever is happening out in space.
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So it was that the giant cosmic ray flare of February 23, 1956, emitting an immense burst of protons up to 25 to 30 GeV, proviclecl the first direct glimpse of the state of things in interplanetary space. Briefly, the leacling ecige of the burst of energetic particles arrivecl promptly at Earth from the direction of the Sun.
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it was the beginning of the concept that ultimately lecl to recognition of coronal expansion en cl the supersonic solar wincl en cl heliosphere. By this time there was an active scientific community interested in such topics as solar activity, cosmic ray variations, en cl geomagnetic storms.
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Only with such cletailecl knowlecige of the cosmic ray particles wouIcl it be possible to infer their origin. Attention turned first to silicon crystals, and a Tong program of clevelopment in collaboration with A
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It is a novel pyroelectric scheme involving a thin sheet of plastic that has been polymerized in the presence of a strong electric field perpendicular to the plane of the plastic, the final sheet is electrically polarized and carries a positive electric charge on one surface and a negative charge on the other. A dust particle or heavy nucleus penetrating though the sheet vaporizes a small area, thereby releasing the charges.
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LASR macle it possible to consoliciate the instrument clevelopment and space research uncler one roof, at the same time providing a home for theoretical research clirectly or loosely connected with the results of the ongoing space experiments. Equally important in Simpson's eyes was the immersing of the students in all aspects of space research.
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Simpson en cl his students en cl coworkers built the first cosmic ray (energetic particle) detectors to visit Mars (in 1965)
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at solar minimum, with the polar magnetic fielcis of the Sun stretched radially out through space. The speculation that the galactic cosmic rays penetrate freely into the Sun along this raclial fielcl was found to be incorrect.
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PARTICLE ACCELERATION It is remarkable that wherever one looks around the solar system en cl wherever one can probe the galaxy, there are vigorous populations of fast particles, from cosmic rays to trapped particle belts in the magnetic fields of planets. The mechanisms responsible for accelerating these particles above the general thermal background!
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Roth more recently have shown that ion cyclotron waves are another possibility, both processes being remarkably efficient uncler the right circumstances. Simpson was particularly interested in the ultimate acceleration problem (i.e., the origin of the galactic cosmic rays)
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to energies of the order of 100 MeV as they pass through the termination shock. COSMIC RAYS IN THE GALAXY Finally, then, turning attention to the galactic cosmic rays: The isotopic studies revealecl that i°Be is almost entirely missing from among the cosmic rays.
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Subsequent evaluations of other unstable nuclei confirm the general 2 x 107 year cosmic ray residence time within the magnetic fields of the galaxy. So the study of isotopes provides insight into the galactic range of the cosmic rays.
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It is an honor among the junior scientific staff of the Enrico Fermi Institute to be appointed the Compton lecturer for an academic quarter. The lectures are invariably excellent, en c!
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The solar cosmic rays of February 1956 and their propagation through interplanetary space.
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The age of galactic cosmic rays derived from the abundance of i°Be. Astrophys.
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Isotopic composition of galactic cosmic ray elements from carbon to silicon: The CRRES satellite investigation. Astrophys.
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Isotopic abundances of Fe and Ni in galactic cosmic ray sources. Astrophys.
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