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Studies of Heavy Nuclei at Jefferson Lab The use of the nucleus as a highly-condensed-matter laboratory is an important component of the Jefferson Lab physics program. In it one can study the modification of the elementary amplitudes for many processes by the strongly interacting nuclear medium. At the present time, we have obtained an enormous amount of real-photon data on the proton (g1) and a large amount on the deuteron (g2) as well, from which one can extract the elementary amplitudes on the proton and the neutron. As we are now seeing from the ongoing analysis of the g3a data (see Section B above), we have ample data on 3He and 4He as well. What is lacking, obviously, are data on heavier nuclei. Just as fundamental studies of the elementary particles are best performed with nucleon targets and fundamental studies of few-body forces are best performed on the lightest nuclei, so it is that fundamental studies on the properties of nuclear matter are best performed on the heaviest nuclei. It is fortunate that the dominant mode of decay of a highly excited very heavy nucleus is via the fission channel, because fission fragments are energetic and highly ionizing, so that their detection is very efficient. We have exploited this fortunate circumstance to study the absorption of photons in heavy nuclei at medium energies at SAL and at high energies at JLab (the g5 experiment). These results constituted the thesis work for two of our Ph.D. students, Juan Carlos Sanabria (the SAL results) and Catalina Cetina (the JLab results) [San99, Cet01]. Dr. Sanabria is now Associate Professor of Physics at the Universidad de los Andes in Bogota, Colombia and Dr. Cetina holds a Postdoctoral Fellowship at the U.S. Naval Research Laboratory in Washington, DC. A long article on the JLab results was published in Phys. Rev. C last year [Cet02]. We are continuing this work on the theoretical side by collaborating with Dr. I. Pshenichnov, a Center for Nuclear Studies Scholar, on intranuclear-cascade-model calculations, and we plan eventually to continue our experimental work at HIGS as well. |
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