A paper by Michael Wiescher published in
the American Physical Society’s Physics journal recently traces development
in research on nuclear reactions that happen in stars. The article titled
“Cosmic alchemy in the laboratory” covers both theoretical and experimental
advances in the field, as well as a discussion of the role of such reactions
in creating the variety of physical elements. Wiescher is the Freimann
Chair of Physics, Director of the Nuclear Science Laboratory and Director
of the Joint Institute for Nuclear Astrophysics.
The paper points forward to three major initiatives
for the construction of new underground accelerator facilities, including
the Dakota Ion Accelerators for Nuclear Astrophysics (DIANA) at Homestake
mine in South Dakota, a collaboration among the University of Notre
Dame, the University of North Carolina, Western Michigan University
and Lawrence Berkeley National Laboratory. Other proposed underground
accelerator facilities are at a salt mine in the United Kingdom and
an abandoned train tunnel in Spain. Underground laboratories shield
experiments from high-energy cosmic raise that are a distracting background.
The experiments grow out of theoretical advances
in recent years in the field of stellar reactions and stellar evolution.
Scientists have long known that fusion of hydrogen in stars produces
helium, helium burning produces carbon, and subsequent burnings produce
neon, oxygen, silicon, iron and nickel. The sequence depends on the
mass of stars and leads variously to white dwarfs, red giants and other
categories of stars in their life cycles. But because the process involves
billions of years, researchers must find creative ways to conduct measurements
that lead to more understanding of the evolution process and the associated
nucleosynthesis. Complementary to the development of underground accelerator
laboratories, equipment such as the newly designed St. George recoil
mass separator at Notre Dame will offer alternative ways to study stellar
reactions.
"Rapid developments in the study of low-energy
nuclear reactions should help researchers overcome a number of the challenges
that have hampered past work," Wiescher wrote. "Theoretical methods
have been substantially improved and allow a much more reliable extrapolation
of the existing data into the Gamow window of stellar burning (the range
of energies of particles that fuse at a given temperature). However,
theoretical models are often insufficient in describing the complex
interaction and interference of the resonant and nonresonant reaction
contributions in the Gamow range. There are also possible effects, which
occur near the particle threshold, such as contributions from subthreshold
resonances or additional nonresonant contributions that have to be taken
into account but are only accessible to direct measurement."
Michael Wiescher is a Fellow of the American
Physical Society and the Humboldt Gesellschaft in Germany. In 2003,
he was awarded the Bethe Prize of the Divisions of Nuclear Physics and
Astrophysics of the American Physical Society. He has given more than
100 invited presentations at national and international conferences
and nearly 100 seminars and colloquia and has published more than 200
refereed articles.
Link to American Physical Society journal article: http://physics.aps.org/articles/v2/69
September 8, 2009