faculty

Professor Emeritus of Chemistry
Ph.D., Massachusetts Institute of Technology

Nuclear Chemistry and Gamma-Ray Spectroscopy of "Hot" and "Cold" Nuclei, Radiochemistry

Phone: (734) 764-1438
E-mail: hcg@umich.edu  
Fax: (734) 647-4865

What are nuclei really like? This is the primary question of nuclear science--a blend of chemistry and physics, with a dash of computer science (for data acquisition and analysis) and nuclear engineering (for neutron facilities). Partial answers to the question come from small scale experiments; the simple ones (based on one discipline or technique) have been done, but interesting questions remain to be answered by a suitable blend of techniques. We emphasize the studies of radioactive materials that require chemical isolation and purification combined with high precision measurements of radiations accompanying radioactive decay.

Some projects are chosen because of their obvious applications (e.g., analyzing nuclear waste, or contributing to a catalog of gamma-ray spectra) and others are chosen "just for fun" (e.g., characterizing the decay of ²³⁴Th and the Pa isomers it produces). Most of our laboratory work is carried out in the Phoenix Memorial Laboratory (PML), which adjoins the Ford Nuclear Reactor on the Ann Arbor North Campus. Here we produce radioactive materials by neutron irradiations, develop chemical separations, and study the gamma rays emitted in radioactive decay.

The components of a mixture of radioactive materials are most likely to be identified by gamma-ray spectroscopy, but the relation between number of decays and number of gamma rays is generally not precisely known (typical uncertainties are 3-10%). We are developing techniques to allow measuring this property much more precisely (0.1-0.6% uncertainties). A key part of the technique is knowing the purity of our samples from analysis of the fractions, pure and impure, obtained during a purification process even though the mass of each important component may be less than a nanogram. The technique has been applied to several reactor-produced nuclides that can serve as calibration standards.

In some cases we collaborate with groups from other institutions (e.g., use magnetic lens to separate products of beams of heavy ions from accelerators at Michigan State University and Notre Dame, or use Gammasphere at Lawrence Berkeley Laboratory in California to study ²⁵²Cf). These collaborations provide physical means of isolation and identification of radioactive materials when chemical techniques are not feasible.

REPRESENTATIVE PUBLICATIONS

1. E Schonfeld, H Janssen, R Klein, J Hardy, V Iacob, M Sanchez-Vega, HC Griffin, MA Ludington. "Production of 60Co sources for high-accuracy efficiency calibration of gamma-ray spectrometers" Appl. Radoiat. Isot. 2002, 56, 215.
2. HC Griffin, C Sumithrarachchi. "Measurement of absolute gamma/beta ratios" Trans. Amer. Nuclear Soc. 2001, 85, 234.
3. See ²⁴Na, ⁴⁹Ca, and ⁸⁸Rb spectra at http://id.inel.gov/gamma/actinide.html
4. TW O'Donnell, FD Becchetti, J Brown, JW Janecke, MY Lee, RS Raymond, DA Roberts, RS Tickle, HC Griffin, R Ronningen. "Isotope Yields with a Solenoid-based Fragment Mass Analysis System - Prospects for Exotic Isotope Studies in the 10 ² Z ²30 Range" Nucl. Instr. Methods A 1999, 422, 513.
5. JK Hwang, et al (GANDS collaboration). "Close Doublet Structures in ¹⁰³Mo, ^103,109Ru, and Neighbours: Rotation-alignment for the Half-filled h11/2 Subshell?" J. Phys. G: Nucl. Part. Phys. 1998, 24, L9.