Geoffrey Grinyer was announced winner of the 2007-08 Thesis Prize Competition by the Division of Nuclear Physics (DNP) of the Canadian Association of Physicists (CAP). This prize is given in Experimental or Theoretical Nuclear Physics to a student who is obtaining his/her Ph.D. degree from a Canadian University in the current or prior year. Dr.Grinyer received his Ph.D. from the University of Guelph in 2007 for the work “High Precision Half-Life Measurements for Superallowed Fermi Beta Decays.” The selection committee formed by David Hutcheon (representing TRIUMF), Jean Barrete (McGill University) and Kumar S. Sharma (University of Manitoba) unanimously voted his paper as number one.
It is exciting to see a Canadian student who worked under the supervision of Carl Svensson at TRIUMF obtain such merit. Grinyer’s precision of half-life measurements has increased our understanding of decay properties. In order to understand the significance of his work it is important to review some fundamental physics. Beta decays occur when there are either too many protons or too many neutrons in a nucleus, making the system unstable. When this happens one or more of the excess protons or neutrons are transformed into the other so the nucleus can move into a more stable state. For some beta decays the structure of the nucleus is very similar before and after the beta decay. This special type of decay is a “superallowed beta decay” and it’s the same kind Grinyer studied. The half-life is a measurement of time that tells how long it takes for half of the sample to decay. Grinyer specifically looked at the beta decay of Gallium 62 (62GA) to Zinc 62 (62ZN). In this process, Gallium 62 went from having 31 protons and 31 neutrons to Zinc 62 with 30 protons and 32 neutrons. In simple terms, the number of protons and neutrons in the atom’s nucleus changed but their sum remained the same. The precision of Grinyer’s half life measurement of this decay was quite astounding, 116.110 ± .25 miliseconds. This represents the single most precise measurement to date for any superallowed beta decay half life.
According to Carl Svensson, "Geoff's Ph.D. thesis is a truly outstanding contribution of original research. He describes not only the development and demonstration of a new, and widely applicable, experimental technique to allow high-precision nuclear lifetime measurements through gamma-ray counting, but also presents the single most precise half-life measurement for any superallowed beta emitter performed to date. These developments have made a very important contribution to the ongoing world-wide effort to improve Standard Model tests through high-precision superallowed beta decay measurements. It is truly an honor for Geoff that his original work in this field has been recognized through the 2008 Division of Nuclear Physics Thesis Prize."
All the data for Geoff Grinyer's Ph.D. thesis was taken with the 8pi Spectrometer and the 4pi beta counting facility at TRIUMF's ISAC-I facility. Following completion of his Ph.D. at the University of Guelph in December 2007, he was awarded the prestigious inaugural Gregers Hansen Research Fellowship at Michigan State University's National Superconducting Cyclotron Laboratory where he is currently based.
Banner photo :One hemisphere of the 8pi spectrometer used by Geoffrey Grinyer at TRIUMF's Isac-I facility.
Maria Jose Crousillat
TRIUMF's Communications Assistant