Information
for Prof. Bradley M. Sherrill
University Distinguished Professor of Physics/National Superconducting Cyclotron Laboratory
email: sherrill at nscl.msu.edu
The rise of nanotechnology is garnering much attention for its ability to construct objects out of individual atoms and molecules, at a scale roughly a billion times smaller than the objects we encounter in our everyday lives. In parallel to nanotechnology's achievements; my research is to develop the capacity to construct objects on an even more minute scale, that of the atomic nucleus 100,000 times smaller. It is probably to best to describe this as femtotechnology.
Atomic nuclei are characterized by their number of protons and neutrons. The number of protons determines the element — one for hydrogen, two for helium, three for lithium, and so on — while the number of neutrons determines the particular isotope of that element. Heavy water, for example, is composed of water molecules with a heavy isotope of hydrogen, 2 H, which has one rather than zero neutrons in its nucleus. The two denotes one proton plus one neutron in the nucleus. Approximately 270 isotopes are found naturally. However, many more isotopes, nearly 7000 in total, can be produced by particle accelerators or in nuclear reactors. These isotopes are radioactive and spontaneously decay to more stable forms.
There are several reasons why a latent demand exists within the scientific community for new, rare isotopes. One is that the properties of particular isotopes often hold the key to understanding some aspect of nuclear science. Another is that the rate of certain nuclear reactions can be important for modeling astronomical objects, such as supernovae. And of course, the pursuit of ever more exotic isotopes sometimes advances basic understanding in unexpected ways. A recent, remarkable example was our discovery of 42 Al, whose existence was thought to be unlikely. The result indicates that nuclei can bind more neutrons than previously predicted.
The NSCL is one of the leading research laboratories in the production and study of new isotopes. A new U.S.-based isotope science facility likely will contribute several major advances in this field. One of my major efforts has been the development of this concept and service as a leader in the scientific community trying to make this facility a reality.
Femtotechnology gives scientists access to designer nuclei with characteristics adjusted to the research need. For example, super-heavy isotopes of light elements, such as lithium, have a size nearly five times the size of a normal lithium nucleus. The existence of such nuclei allows researchers to study the interaction of neutrons in nearly pure neutron matter, similar to what exists in neutron stars.
The approach that I have helped develop for production of new isotopes is called in-flight separation; where a heavy ion, such as a uranium nucleus, is broken up at high energy, producing a cocktail beam of fragments that are filtered by a downstream system called a fragment separator. The efficiency of this technique can be nearly 100% and we are able to identify a single ion out of 10 15 other particles.
Spring Semester 2007: ISP209
Spring Semester 2008: ISP209
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