John Norbury has broad interests in several areas of
theoretical physics including nuclear physics, particle physics, field theory,
cosmology and the problem of space radiation.
His work in nuclear physics has involved electromagnetic processes in
relativistic nucleus-nucleus collisions. In particular, collisions accompanied
by the removal of few nucleons have, in certain cases, cross sections comparable
to those of strong interactions. A primary concern is to understand processes
that occur in the presence of very strong electromagnetic fields, precluding the
usual perturbative treatment of quantum electrodynamics. Apart from the
intrinsic physics interest, this is important in estimating the lifetimes of the
nuclear beams which will be installed in the Relativistic Heavy Ion Collider at
Brookhaven and the Large Hadron Collider at CERN.
Norbury's work in particle physics and field theory has been in collaboration
with physicists at the Thomas Jefferson National Accelerator Facility. He is
particularly interested in quark bound state systems and the two body bound
state problem in field theory. He has shown how to correctly incorporate the
one-gluon exchange and quark confining interactions into relativistic bound
state equations in momentum space. Norbury is also interested in alternative
production mechanisms in the search for the Higgs boson and has calculated cross
sections for Higgs boson production in nuclear collisions via two-photon
exchange mechanisms. His most recent project is to extend this work to weak
boson interactions produced in nuclear collisions, with regard to the search for
the intermediate mass supersymmetric Higgs boson. In addition, Norbury has
interests in cosmology and is currently working on models of a decaying
cosmological constant and their relevance to inflation, quantum tunneling and
the age of the universe.
Norbury has also worked extensively with NASA over the past decade and is
especially interested in the problem of how to protect astronauts from cosmic
radiation. He has been a co-recipient of several NASA awards and has co-authored
a book on cosmic ray interactions.
When astronauts travel into space they can receive a dose of radiation from
one of three sources, from particles trapped in the Earth's radiation belts
(trapped radiation), from energetic particles emitted from the Sun (energetic
solar particles) or from cosmic rays which have their origin from our own galaxy
(galactic cosmic rays). For missions in low Earth orbit, such as the space
shuttle or the future International Space Station, the most important concern is
from trapped radiation and energetic solar particles. For long duration human
missions, such as a return to the moon (lunar base) or a two year Mars mission,
the radiation of most concern is from energetic solar particles and galactic
cosmic rays. For example, one of the largest solar flares in recorded history
occurred in August 1972 between the Apollo 16 and 17 missions. Had astronauts
been on the lunar surface at that time they would have received a lethal dose of
radiation.
NASA is currently planning for a human mission to Mars. It is of paramount
importance to solve the space-radiation problem for this mission. What needs to
be understood are the fundamental processes that occur when a cosmic ray
particle initiates a nuclear reaction within the wall of a spacecraft. Thus
Norbury's project involves applied nuclear and particle physics. Aspects of the
project involve electromagnetic and strong interaction processes in
nucleus-nucleus collisions and pion and kaon production in proton-proton
collisions. Norbury works closely with scientists at NASA Langley Research
Center in Virginia and Johnson Space Center in Houston, Texas. Students learn
about a variety of topics in nuclear and particle physics and astrophysics and
gain extensive computational experience as well as an understanding of general
issues in radiation and radiation biology.
