Nuclear physicist Henry Gabriel “Hank” Blosser died in East Lansing, Michigan, on 20 March 2013 at the age of 85.
Henry was born in Harrisonburg, Virginia, on 16 March 1928. After studying business for a year at the University of Virginia, he served two years in the US Navy. He returned to UVA, where he received his BS in math in 1951 and his MS in 1952 and PhD in 1954, both in physics. His PhD thesis was “Large-angle scattering of electrons at 65 kilovolts,” and his thesis adviser was Frank Hereford, later president of UVA. Henry then joined Oak Ridge National Laboratory and soon became group leader of the cyclotron project there. His group took advantage of the increasing power of digital computers to determine the acceleration properties of a new generation of cyclotrons that promised to overcome the limitations in energy and precision of classical Lawrence cyclotrons.
In the 1950s Michigan State University (MSU) decided to increase the strength of its rapidly growing physics department by developing a new heavy-ion cyclotron. Henry saw an opportunity to put into practice and further develop his new ideas. He arrived at MSU in mid 1958; at age 30, he was an associate professor and director of an unfunded cyclotron laboratory.
Although federal funding was in one of its recurrent low periods, by October 1961 Henry had completed a cyclotron design in collaboration with Morton Gordon, had written proposals, and had received funding from NSF to build a precision cyclotron, now known as the K50. Although the physics department had little relevant infrastructure when Henry arrived, and although his design had many novel features, he and his team set up the K50 in a new building and made it operational in just three and a half years.
The K50 had superb properties: Its precision proton beams set a new standard for cyclotrons and made possible experiments with resolutions comparable to Van de Graaff accelerators. Henry participated in only a single pure nuclear-physics experiment at MSU, in which the laboratory’s high-resolution capability was used to delineate in unique detail the nature of bismuth-208 excitations. That established the feasibility of the many experiments that followed and established the unique strength of the Cyclotron Laboratory. Over the next 14 years, the K50 supported a research program that put MSU nuclear physics on the map.
Henry developed a new generation of superconducting cyclotrons that redefined the nature of cyclotrons. The driving idea was that, compared with a typical cyclotron, the average magnetic field could be three times larger and the radius three times smaller for a given energy. That reduced the mass of the magnet steel by a factor of 15–20 and the cost of the cyclotron as well as that of the necessary building infrastructure. Henry received NSF funding to build a demonstration magnet and showed that sufficiently precise fields could be produced.
That result attracted additional NSF funding to turn the magnet into a K500 cyclotron. During K500 construction, Henry led a Midwestern group of physicists from 19 institutions that submitted a proposal to build a coupled cyclotron facility at MSU: The K500 would inject its beam into a K1200 cyclotron to yield particle energies up to 200 MeV/nucleon. During its first exercise in setting priorities for US nuclear physics, the Nuclear Science Advisory Committee approved the construction. For a complex set of reasons, the scheme was carried out in two stages: In the first, the K1200 was injected by an electron cyclotron resonance ion source, and in the second, it was coupled with the K500 as originally planned. The coupled system has, since its inception in 2001, set the standard for research with radioactive beams.
Henry retired in 2003, but he continued his earlier interest in developing cyclotrons for cancer therapy. He used his experience in cyclotron miniaturization to build a neutron-producing machine so small that it could be mounted on a gantry and rotated around the patient being treated, which helped reduce damage to tissue surrounding the tumor. The cyclotron was installed at Harper Hospital in Detroit, and from 1992 to 2012, it treated more than 2000 patients. Later Henry developed and patented a cyclotron that produced beams of 250-MeV protons for cancer therapy; two have been built and three more are under construction.
Probably best characterized as a builder, Henry had a passion for designing new accelerators with forefront properties, thoroughly understanding their operation, and building them with a high standard of technical care. He carried over that passion into developing the MSU Cyclotron Laboratory, now the National Superconducting Cyclotron Laboratory; he served as either the lab’s director or codirector (with one three-year hiatus) between 1958 and 1989 and built a team that has earned the lab the highest ranking in US nuclear physics. In 2009 MSU was chosen by the US Department of Energy to be the home of the Facility for Rare Isotope Beams, the major new US facility for nuclear physics that will be strongly competitive on the world scene.
Henry received numerous recognitions and awards for his work, including the 1992 Tom W. Bonner Prize in Nuclear Physics from the American Physical Society. On the side, he was an avid backpacker and grower of heirloom tomatoes.
