Edwin L. Aguirre
The nuclei that exist inside atoms of elements readily found in nature — such as carbon, oxygen, aluminum, iron, copper and gold — consist of fixed combinations of protons and neutrons. But if these combinations are tampered with, the nuclei become unstable.
In the hundred years since modern nuclear physics was born, scientists have managed to observe less than half of the thousands of such rare “isotopes
” they expect should exist; the rest are still waiting to be discovered. The reason is that many of them last for only fractions of a second before they change back into more stable forms. These exotic isotopes do not occur naturally — they are forged in violent cosmic processes, including the cataclysmic explosions of stars called supernovae, which are responsible for the synthesis
of most of the elements in our world. Here on Earth, the isotopes are produced in laboratory facilities with particle accelerators or in nuclear reactors.
“Our investigation ventures into the ‘terra incognita’ of the varied combinations of neutrons and protons that make up matter in our universe,” says Chowdhury. “Exotic, short-lived and highly unstable atomic nuclei hold the key to understanding how elements are synthesized in stars and to developing next-generation nuclear reactors for producing safe and sustainable energy.”
Their research represents the final stages of a $2 million grant from the U.S. Department of Energy (DOE), with Lister and Chowdhury as co-principal investigators. Lister was a senior scientist at Argonne National Laboratory
before joining the UMass Lowell faculty last year. Located just outside of Chicago, Argonne is one of the largest national lab facilities of the DOE for scientific and engineering research in energy, the environment and national security. The grant, which originated as a national lab–university collaboration while Lister was at Argonne, was transferred fully to UMass Lowell after he moved to the University.
A Leading Player in the Field
In this study, beams of neutron-rich isotopes separated by mass are extracted from an intense fission source and studied with cutting-edge spectroscopic tools at Argonne.
“The rare isotopes produced at Argonne can be trapped and isolated electromagnetically so we can measure their masses as well as beta decays and transmutation properties,” explains Chowdhury. “Or they can be accelerated by a superconducting heavy-ion linear accelerator so we can measure their excitations and characteristic radiation.”
It is the availability of these short-lived, neutron-rich isotopes at Argonne that makes the project feasible.
“We are responsible for assembling state-of-the art experiments to measure the decays of these isotopes, focusing on the gamma-rays and delayed neutrons for which we have special expertise and tools,” notes Lister. “The project involves significant effort in developing hardware and detectors, coupled with a strong commitment to fostering the education and training of the graduate students and post-doctoral researchers.”
Recently, the DOE partnered with Michigan State University to build a $680 million high-power, superconducting linear accelerator
on the MSU campus for generating and accelerating rare isotopes. The facility is expected to come online in 2021.
“Our current research is a step in this direction and paves the way for these future studies of rare, highly unstable isotopes,” says Chowdhury. “It also positions UMass Lowell as a leading player in this field in the coming decade.”