Discovery of the Trapped Radiation

ithout a doubt, the most momentous event during this period of early space exploration was the discovery, from the data obtained from Explorers I and III, of what we dubbed initially as simply the high-intensity radiation. It has come to be known commonly as the Van Allen Radiation Belts. This discovery was a serendipi­tous event. The original purpose of the experiment had been for a rather straightfor­ward extension of the cosmic ray research that had been under way for many years. That objective was immediately overshadowed when the new discovery thrust itself upon us.

There have been many accounts of the discovery, some of them misleading, incom­plete, or contradictory. In the interest of historical accuracy, there is heavy reliance in this work on primary documentation, that is, material that was written by direct participants at the time of the activity. Those include a variety of archival materials, personal files, and many papers and other published and unpublished accounts.1,2’3’4 There was secondary dependence on the recollections of direct participants, including a number of unpublished exchanges.5

It should be noted that there is a relative lack of primary documentation for one key period—much of the month of April 1958. Laboratory notebooks and personal journals of the four major participants, Van Allen, McIlwain, Ray, and this author, are strangely deficient. It was a time of unusually intense activity—all of us were so completely absorbed in following up on the exciting new findings, that our normal habits for record keeping appear to have been set aside for a while.

Van Allen, the principal investigator and intimately involved in all aspects of the project, was an unusually meticulous record keeper, and he retained his many journals, diaries, notebooks, day-to-day notes, calendars, meeting files, travel records, letters,

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and so on. As mentioned earlier, they reside now, along with complete cataloging, as a professionally maintained collection by the Department of Special Collections in the University of Iowa Libraries.

I was responsible for the cosmic ray instrument development, for our field activi­ties, and for designing, setting up, and running the University of Iowa data-processing facilities. Although participating at times in the data analysis effort, much of my atten­tion was directed to the instrumentation, operational, and data-processing activities. My work is also thoroughly documented. It includes extensive personal journals, notebooks, calendars, meeting files, travel records, photographs, sample data records, letters, and so on. Arrangements have also been made to preserve most of my materials as another special collection in the University of Iowa Libraries.

Carl McIlwain concentrated on developing a thorough understanding of the behav­ior of Geiger counters in the presence of intense radiation and on working with Ernie and Van in pondering, unraveling, and describing the new phenomenon. Carl’s record keeping was intermediate in scope. His records, combined with his keen recollection of events that took place during the 1950s, have been instrumental in resolving some of the conflicting details. Discussions are under way about also placing Carl’s records in the University of Iowa Libraries.

Ernie Ray took charge of the initial processing and plotting of the Explorer I and III flight data at Iowa City. He was an enthusiastic participant, throughout the period, in developing an understanding of the physical processes being observed. Ernie’s record keeping was nonexistent—his shirt pocket served as his file cabinet. Having died in 1989, his personal memories can no longer help us. His contributions to this account are based primarily on the recollections of his wife, Mary, some of his data plots, and a few short notes.