Space Science & Space Physics Tribute

Edward L. Chupp (1927–2017)

This pioneer in high-energy solar physics devised instruments for observing solar and cosmic ray emissions with which he detected, for the first time, nuclear gamma rays from solar flares.

By and Martin A. Lee

Edward L. Chupp, a professor of physics at the University of New Hampshire, died on 21 February 2017 at the age of 89. Ed, as he was known to his friends and colleagues, was born in Lincoln, Neb., on 14 May 1927. After high school and a stint in the U.S. Navy at the end of World War II, he enrolled at the University of California, Berkeley, in engineering. At the suggestion of his brother, Warren, he changed his major to physics, eventually receiving his Ph.D. from Berkeley in 1954.

At that time, scientists there and in other places who studied nuclear and high-energy physics often worked on cosmic ray experiments; those rays are a convenient source of high-energy particles.  After earning his Ph.D., Ed worked at the University of California Radiation Laboratory at Livermore, now known as the Lawrence Livermore National Laboratory, on experiments focused on cosmic rays that were neutrons, setting up a neutron monitor at Makapu‘u Point in Hawaii in cooperation with the University of Hawai‘i.  Secondary neutrons in the atmosphere are a robust proxy for primary cosmic rays in the near-Earth environment. By then, solar cosmic rays had been detected at high-latitude neutron monitors, and the low latitude of Hawaii offered a different energy threshold for measuring their spectra.

Ed continued his atmospheric radiation studies at the Boeing Company before coming to the University of New Hampshire (UNH) in 1962, shortly after the 1957–1958 International Geophysical Year and the discovery of Earth’s radiation belts. He came to UNH to work with Professors Jack Lockwood and Bill Webber in atmospheric, space, and solar high-energy radiation. Ed soon established his own research program, studying neutrons and gamma rays in the near-Earth environment. That program resulted in the Gamma Ray Monitor (GRM), which was flown on the seventh Orbiting Solar Observatory (OSO-7).

A Flair for Gamma Ray Discoveries

GRM turned out to be a groundbreaking instrument, putting Ed squarely at the center of observational high-energy solar physics, where he stayed for the next 40 years. GRM’s single 3 × 3 inch (7.6 × 7.6 centimeter) thallium-activated sodium iodide detector recorded gamma radiation from the massive solar flares of 4 and 7 August 1972 with a wavelength associated with the formation of deuterium. This was clear evidence of free solar neutrons created by high-energy ion collisions during the two flares. Detected as well were gamma rays at other wavelengths, indicative of specific excited nuclear states of carbon and oxygen and of electron-positron annihilation. Ed and his colleagues reported these first observations of gamma rays associated with solar flares in a seminal paper in Nature in 1973.

Edward Chupp works on some equipment in the UNH physics building in 1963. credit: Milne Special Collections and Archives Department, UNH Library, Durham
Chupp in May 1983 at UNH. Credit: Jack Adams, UNH photographer. Milne Special Collections and Archives Department, UNH Library, Durham

The landmark solar flares that produced those gamma rays were also prodigious sources of energetic protons in space that were detected with neutron monitors in New Hampshire and elsewhere. The conventional wisdom was that protons in space were colliding with the ambient solar atmosphere and producing gamma radiation over the course of many tens of minutes. This thinking prevailed until NASA’s Solar Maximum Mission, which was launched on 14 February 1980 carrying Ed’s follow-up instrument, the Gamma Ray Spectrometer (GRS).

Equipped with seven of the detectors used by GRM, GRS registered many solar flares with nuclear gamma ray emissions but few protons in interplanetary space. Furthermore, most of these flashes of gamma rays were short-lived, often lasting only about a minute. These few and brief gamma emissions served to completely revise the understanding that Ed and others had of the August 1972 events and their production of solar energetic particles. The consensus today holds that the gamma rays arise from a population of energetic particles different from those detected in space.

Long-Duration Emissions

GRS also recorded readings from what were later to be called long-duration gamma ray flares, whose gamma emissions lasted for tens of minutes to hours and came from ions roughly 500 times more energetic than those that produced the August 1972 gamma radiation. These long-duration flares were later studied in greater detail with data from the Compton Gamma Ray Observatory, aloft from 1991 to 2000, and the Fermi Gamma-ray Space Telescope, which surpassed a decade in space just this past June. Long-duration flares remain an active topic of research.

Ed Chupp authored his final paper in 2009 on this subject of very high energy gamma ray flares, 36 years after the publication of the August 1972 observations. Interspersed within all this research in high-energy solar physics was a vigorous balloon program in gamma ray astronomy and a 1976 monograph on this astronomy subfield entitled Gamma-Ray Astronomy: Nuclear Transition Region.

Ed maintained his teaching responsibilities until his retirement in 2006. Many researchers in the field, several now retired themselves, owe their doctoral training to Ed. A few years after retiring, Ed moved to Connecticut to be closer to family.

Predeceased by his wife, Mary, almost 20 years earlier, Ed is survived by his children, Professor Timothy Chupp, Christine Greenwood, and Dr. Geoffrey Chupp, and eight grandchildren.

Ed was a member of the AGU for 51 years.

—James M. Ryan (email: [email protected]) and Martin A. Lee, Space Science Center, University of New Hampshire, Durham

Citation: Ryan, J. M., and M. A. Lee (2018), Edward L. Chupp (1927–2017), Eos, 99, Published on 27 July 2018.
Text © 2018. The authors. CC BY-NC-ND 3.0
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