The simplest bound system of neutrons and protons is the deuteron, consisting of one proton and one neutron. In the language of the theory of the strong interaction, quantum chromodynamics (QCD), it is made of six valence quarks (3 up and 3 down), plus the quark-gluon sea. In the standard proton-neutron picture, the deuteron's shape is largely determined by the exchange of a pion, which leads to strong, noncentral "tensor" interactions.
Color polarizabilities: response of the color electric Ec→ and magnetic Bc→ fields in the nucleon when the nucleon is polarized in the direction given by the spin vector S.→
The structure of the deuteron, the nucleus of the deuterium atom, is of prime importance to nuclear physicists. The deuteron is a bound state of one proton and one neutron, and it is the nucleus most often used in measurements of neutron structure. Studies of the deuteron have helped determine the role of non-nucleonic degrees of freedom in nuclei and the corrections from relativity. A recent series of Jefferson Lab measurements have focused on the role of quarks in the structure of the deuteron.
Do new data on the nucleon spin agree with what we expected in the high x_bj region? Left: Neutron spin asymmetry A1n; Right: Spin directions of quarks inside the nucleon.
The Quark-Meson Coupling (QMC) model, a theory which takes the radical step of incorporating self-consistent changes in the quark structure of a nucleon when it is bound in matter, has been transformed into a theory of quasi-nucleons interacting through many-body forces. This adjustment allows the QMC model to be related to the time-honored descriptions of the nucleus where nucleon structure was supposed to play no role. Of course, in experiments conducted at very high energies, it is customary to see the nucleus as a collection of quarks interacting via the exchange of gluons.
Jefferson Lab continues to integrate the fruit of superconducting radiofrequency (SRF) R&D into the production of higher-performing accelerator components. One dimension of this is a program to leverage recent technological developments in the design and implementation of higher quality standards and more efficient techniques for the chemical processing, clean handling and assembly of accelerator components.
The purpose of this collaboration between the University of Florida (UF; David Gilland, PI), the University of South Florida (USF; Claudia Berman, Maria Kallergi, PIs) and Thomas Jefferson National Accelerator Facility (Jefferson Lab) is to design, build and evaluate compact, mobile, high resolution gamma ray and positron medical imaging devices. The targeted applications are molecular imaging of heart disease and breast cancer. Mobile gantries with articulated arms will position the imaging cameras close to the body.
The Jefferson Lab Detector and Imaging Group in collaboration with Oak Ridge National Laboratory (Dr. Justin Baba), Johns Hopkins University (Dr. Martin Pomper) and the University of Sydney (Dr. Steve Meikle) is developing an imaging methodology that utilizes SPECT and X-ray CT for small animal research. The primary challenging task of this project is to develop a SPECT imaging system to allow molecular imaging of unrestrained and un-anesthetized mice.
