The forum for the public announcement of the discovery of the region of high-intensity radiation was a special meeting in the Great Hall of the National Academy of Sciences at 9:45 AM on Thursday, 1 May 1958. The meeting had been publicized within a large circle of members of the scientific community and media by two letters from Hugh Odishaw, executive director of the U. S. National Committee for the IGY. His first letter, dated 22 April and addressed to members of the U. S. National Committee and its Technical Panels, was headed “Experimental Results for 1958 Alpha.” It read:
Brief papers have been scheduled for the presentation of preliminary data obtained from US-IGY satellite 1958 Alpha. Cosmic ray, micrometeorite, temperature, and orbital data will be described by representatives of the State University of Iowa, the Geophysical Research Directorate, the Jet Propulsion Laboratory, and the Naval Research Laboratory and Smithsonian Astrophysical Observatory. The papers will be presented in the Great Hall of the National Academy of Sciences, 2101 Constitution Avenue, N. W., at 9:45 a. m., Thursday, May 1. The meeting is expected to last about one hour.46
Odishaw followed that letter with a second one six days later that transmitted preliminary copies of the papers (including ours). His transmittal letter read:
As you know from my notice dated April 22, 1958, the President of the Academy has made arrangements to have briefreports on experimental results of1958 Alpha presented to members of the Academy, the American Physical Society, and the local scientific community at a special meeting in the Great Hall of the Academy at 9:45 a. m., Thursday, May 1, 1958…. The enclosures are advance copies of these preliminary reports. They are marked “Not for Release” inasmuch as the Academy is making provision for the orderly public release of the reports at the time of the special meeting noted above.47
As indicated, the session had been precipitated by Van Allen’s disclosure of our radiation belt discovery to Richard Porter and other program officials in mid-April. It
OPENING SPACE RESEARCH
was arranged initially to provide a forum for the exchange of all experimental results obtained thus far from Explorer I, but the agenda was expanded to include some results from Explorers II and III.
Van Allen and Frank McDonald represented our Iowa group at the session. The session was chaired by Porter, in his capacity as chairman of the Technical Panel on the Earth Satellite Program (TPESP), U. S. National Committee for the IGY. The papers were titled as follows48:
Status Reports on Optical Observations of Satellites 1958 Alpha [Explorer I] and 1958 Beta [Explorer II], by J. Allen Hynek and Fred L. Whipple
Scientific Results: The Orbit and Variable Acceleration of Satellite 1958 Alpha, by Charles A. Whitney
The Density of the Upper Atmosphere, by Theodore E. Sterne
The Determination of the Orbit of 1958 Alpha at the Vanguard Computing Center, by Joseph W. Siry
Satellite Micrometeorite Measurements, by E. Manring and M. Dubin Satellite Temperature Measurements for 1958 Alpha—Explorer I, by E. P. Buwalda and A. R. Hibbs
Observation of High Intensity Radiation by Satellites 1958 Alpha and Gamma, by James A. Van Allen, G. H. Ludwig, E. C. Ray, and C. E. McIlwain
The last paper received the most attention—our paper disclosing the discovery of the region of high-intensity radiation. In his oral presentation, Van Allen followed the general structure of our written report, but with substantial elaboration. At the end, he added a discussion of the possible relationship between the radiation seen by the satellites and that detected earlier on Iowa’s Davis Strait rockoon expeditions, on Carl McIlwain’s Fort Churchill rocket flights, and on high-altitude balloon flights. Specifically, paraphrasing his spoken word, Van asserted that the effect must be due to charged particles (as opposed to neutral particles or photons), that it was likely to be bremsstrahlung from electrons confined by the Earth’s magnetic field, and that those electrons were rather closely related to the soft radiation that had earlier been observed in the polar regions.
He sketched some numbers on the blackboard, from which he made a further speculation that, if the particle identification were correct, the flux of electrons must be of the order of 109 per square centimeter per second, that the average energy was of the order of 40 kilovolts, and that the energy flux was of the order of 10 ergs per square centimeter per second.
In his wrap-up, Van Allen discussed the probable relationship of those results with the general theoretical concepts of Chapman and Ferraro, including the probability that the particles were trapped in Stormer-Treiman lunes about the Earth. He mentioned that the observed intensity of radiation should be a source of radio noise (probably not detectable from the ground but possibly by a vehicle above
CHAPTER 12 • DISCOVERY OF THE TRAPPED RADIATION 347
the ionosphere). He suggested that there was most likely an intimate connection between this observed radiation and the occurrence of visible aurorae, and that the radiation intensity above 1000 kilometers probably exceeded 60 milliroentgens per hour.
Van Allen’s presentation was followed by a spirited question-and-answer period that focused primarily on arguments against the observations being due to protons or gamma radiation.
Van Allen’s handwritten speaking notes are preserved in the University of Iowa Libraries.49 His entire lecture and the ensuing discussion were captured on magnetic tape by a reporter from the Voice of America, and later transcribed through the efforts of Hugh Odishaw, Ross Peavey, and John Truesdale of the U. S. IGY staff. That transcription was published as a University of Iowa Physics Department research report,50 and shortly thereafter as a National Academy of Sciences IGY Satellite Report.51
That initial announcement of the belt discovery was quickly followed by presentations in other forums. For example, Van Allen repeated his presentation at the 9-12 June 1958 semiannual meeting of the American Rocket Society in Los Angeles. Ernie Ray represented our group at the Fifth Meeting of the Special Committee for the International Geophysical Year in Moscow, held on 29 July to 9 August 1958. There, a telegram from Van Allen, McIlwain, and me conveyed an early report of Explorer IV results. He reported to the attendees that the new data confirmed our radiation belt findings from Explorers I and III.52
Other authors have published their own accounts of the Iowa radiation belt discovery over the ensuing years, of which some of the most interesting and authoritative are identified in the bibliography and in an endnote.53 Although they are in reasonably good agreement on the general sequence of events, the careful reader will note some differences. A special effort was made in this book to resolve those differences, using primary references as well as personal records and exchanges with Van Allen, McIlwain, and others.