New analytical tools coming on line at the Spallation Neutron Source, the
Department of Energy's state-of-the-art neutron science facility at Oak
Ridge National Laboratory, include a beam line dedicated to nuclear physics
The Fundamental Neutron Physics Beam Line (FNPB) has opened its shutter to
receive neutrons for the first time. Among the nuclear physics studies planned
for the new, intense beam line are experiments that probe the neutron-related
mysteries associated with the "Big Bang."
"Completion of the Fundamental Neutron Physics Beam Line marks a significant
step in the SNS's ramp up to full power, building up to its eventual suite of
25 instruments for neutron analysis," said ORNL Director Thom Mason, who
led the SNS construction project to its completion. "The nuclear physics
community is excited to have this new tool for exploring theories of the origins
of the universe."
Although research at most of the current and future operating SNS beam lines
is directed towards condensed matter and materials research, research at the
FNPB is focused on basic studies in nuclear physics.
"While other beam lines use neutrons as a probe to study materials, the
object for much of the work proposed at the FNPB is the study of the neutron
itself," said University of Tennessee Professor Geoffrey Greene, who holds
a Joint Faculty Appointment with ORNL and who leads the FNPB project. "Among
the questions that will be addressed at the FNPB are the details of the internal
structure of the neutron as well as a careful study of the way in which the
free neutron decays. Such experiments have important implication for fundamental
questions in particle physics and cosmology."
Greene explained that neutrons, which have no electric charge, may nevertheless
have a slight displacement between internal positive and negative charges. The
existence of such a "neutron electric dipole moment" could shed light
on what happened in the early phases of the Big Bang. In particular it could
help to explain why the universe appears to be made entirely of matter without
any antimatter, he said.
While the neutron is stable in most nuclei, when it is liberated (for example
in an SNS neutron beam) it lives for only about 10 minutes. "Precise measurements
of the neutron lifetime help clarify the distribution of chemical elements generated
in the first few minutes of the Big Bang and shed light on the amount of normal
matter—as opposed to dark matter and dark energy—in the universe,"
"Another set of extremely precise studies at the FNPB will address the
interaction between neutrons and simple nuclei and may help to explain universal
'parity' violation," Greene said. "Roughly speaking, parity is the
symmetry that implies that the laws of physics are invariant when 'viewed in
a mirror.' The surprising fact is, at a basic level, the universe appears to
"The challenge remains to understand why this puzzling state of affairs
exists," he said.
Greene noted that the theoretical basis for such symmetry violation --first
outlined several decades ago--was recognized earlier this month with the 2008
Nobel Prize to Yoichiro Nambu.