Simpson receives first O’Ceallaigh Medal for cosmic-ray research

John Simpson, the Arthur Holly Compton Distinguished Service Professor Emeritus in Physics, has received the first O’Ceallaigh Medal for his distinguished contributions to cosmic-ray research.

The International Union of Pure and Applied Physics’ Cosmic Ray Commission and the Dublin Institute for Advanced Studies sponsor the award named for the late Cormac O’Ceallaigh, a cosmic-ray scientist who worked at the Dublin Institute.

Simpson received the medal at the 26th International Cosmic Ray Conference in Salt Lake City and an invitation to present a talk on his award-winning work in Dublin next year.

Simpson has devoted most of his career to the study of cosmic rays. Nuclei of atoms accelerated in our galaxy and traveling at nearly the speed of light, cosmic rays constantly bombard Earth from all directions. Analysis of the rays provides insight into how matter is formed in stars as they are born and as they die.

Simpson’s cosmic-ray research began shortly after World War II, first with instruments aboard B-29s, then aboard icebreakers and hot-air balloons. In 1948, using the Earth’s own magnetic field as an analyzer, Simpson discovered that interplanetary dynamical processes controlled by the sun caused the variations in galactic cosmic-ray intensity on Earth rather than geomagnetic storms, which were a popular explanation at the time.

Then Simpson developed a neutron-monitoring instrument that enabled him to continuously study the long-term intensity fluctuations of low-energy cosmic rays.

By the early 1950s, Simpson had established five neutron-monitor laboratories over a wide range of latitudes extending from the equator to Chicago. During a spectacular solar flare that occurred in 1956, the neutron monitors collected the first evidence pointing to the existence of the heliosphere, a region influenced by the sun’s magnetic field that extends far beyond the planets.

During the International Geophysical Year (1957 to 1958), a collaborative effort to study Earth and the space around it, Simpson’s neutron-monitoring instrument became the standard for conducting cosmic-ray research.

Today, the instrument remains a primary tool scientists use to study cosmic rays at more than 50 monitoring stations around the world.

Simpson also has used outer space as his laboratory to study the composition of cosmic rays and how they are accelerated by the sun’s magnetic and galactic fields. Since 1958, he has served as the lead researcher for 33 instruments flown in Earth orbit and throughout the solar system.

Cosmic-ray detectors built by Simpson’s research team were the first sent on space probes that visited Mars in 1965, Jupiter in 1973, Saturn in 1979 and Mercury in 1980. Simpson’s instruments continue to collect data on a variety of space missions, including the Ulysses probe launched in 1990 to study the sun.

In 1959, Simpson proposed the concept of studying cosmic rays in three dimensions. Ulysses was the first spacecraft to leave that narrow orbital plane of the planets to observe the cosmic rays near the sun’s north and south poles. Simpson’s Ulysses experiment is the cosmic and solar particle investigation now led by Chicago Senior Scientist Bruce McKibben.

Simpson’s team also continues to coax data from his instrument aboard the Pioneer 10 space probe. Launched in 1972 and now 6.7 billion miles from Earth, Pioneer 10 became the first spacecraft to reach Jupiter and the first to leave the solar system.