Spectral structure of the pygmy dipole resonance.
Date
2010-02-19
Journal Title
Journal ISSN
Volume Title
Repository Usage Stats
views
downloads
Citation Stats
Abstract
High-sensitivity studies of E1 and M1 transitions observed in the reaction 138Ba(gamma,gamma{'}) at energies below the one-neutron separation energy have been performed using the nearly monoenergetic and 100% linearly polarized photon beams of the HIgammaS facility. The electric dipole character of the so-called "pygmy" dipole resonance was experimentally verified for excitations from 4.0 to 8.6 MeV. The fine structure of the M1 "spin-flip" mode was observed for the first time in N=82 nuclei.
Type
Department
Description
Provenance
Subjects
Citation
Permalink
Published Version (Please cite this version)
Publication Info
Tonchev, AP, SL Hammond, JH Kelley, E Kwan, H Lenske, G Rusev, W Tornow, N Tsoneva, et al. (2010). Spectral structure of the pygmy dipole resonance. Phys Rev Lett, 104(7). p. 072501. 10.1103/PhysRevLett.104.072501 Retrieved from https://hdl.handle.net/10161/4292.
This is constructed from limited available data and may be imprecise. To cite this article, please review & use the official citation provided by the journal.
Collections
Scholars@Duke
John H Kelley
Werner Tornow
My research interests are in experimental nuclear physics studies performed with beams of neutrons, photons and neutrinos. While the early focus was on polarization phenomena in few-body systems studied mainly with polarized neutrons first at the University of Tuebingen and later at TUNL (Triangle Universities Nuclear Laboratory at Duke University), subsequent activities include experiments in the broad field of weak-interaction nuclear physics.
In 1998 TUNL joined the KamLAND collaboration in Japan to pursue reactor antineutrino oscillation measurements. Supported by the U.S. Department of Energy (DOE), I was the principle investigator (PI) of TUNL’s effort in building the veto detector of KamLAND. At about the same time I became one of the four originators of the Majorana zero-neutrino double-beta decay experiment on 76Ge, which later received DOE funding and is now known as the MAJORANA DEMONSTRATOR. Simultaneously, my group performed two-neutrino double-beta decay experiments to excited states in the daughter nucleus at TUNL and at the Kimballton mine in Virginia. In 2011, the KamLAND detector was modified to search for the zero-neutrino double-beta decay of 136Xe, resulting in the currently most stringent lower limit of larger than 3.8 x 1026 years for the decay half-life time for any zero-neutrino double-beta decay candidate nucleus, corresponding to an effective neutrino mass in the range of 28 to 125 meV, depending on the adopted nuclear matrix element calculations.
When I started my 10-year tenure as Director of TUNL in 1996, the Duke University Free-Electron Laser Laboratory (DFFLL), funded at the time by the U.S. Air Force Medical Free-Electron Laser Program, was already collaborating with nuclear physics faculty at TUNL In November 1996 I was fortunate enough to detect the first high-energy photons produced via Compton backscattering of free-electron laser low-energy photons from electrons circulating in the Duke 1.1 GeV electron storage ring. This was the beginning of HIGS, the High-Intensity Gamma-ray Source (strictly speaking the notation “Gamma-ray” is somewhat misleading; the “Gamma-Rays” produced at HIGS are actually high-energy photons and do not originate from nuclei, as gamma-rays do). After years of work sufficient funding was raised from DOE and Duke University to upgrade HIGS and convert it into a Nuclear Physics research facility operated by TUNL. As a result, I had to enlarge my nuclear physics portfolio to now include many-body physics as well, in order to manage the research opportunity provided by this worldwide unique facility. Here, nuclear structure experiments performed with mono-energetic incident photons in the 2 to 15 MeV energy range were of special interest for the many users from all around the world.
After retiring from teaching at Duke University in 2011, my research focus at TUNL’s Tandem Accelerator Laboratory was on experiments with mono-energetic neutron beams in the 0.5 to 30 MeV energy range. Here, nuclear fission studies have played a major role for about 12 years. In addition, my research group performed measurements to help quantify the neutron-induced background in zero-neutrino double-beta decay searches on 76Ge, 130Te and 136Xe as well as in associated shielding materials, including 40Ar. Furthermore, we studied reactions of importance for the National Ignition Facility (NIF) to help better understand the complicated physics governing the plasma generated in inertial confinement fusion laser shots at Lawrence Livermore National Laboratory. All these activities were supported by the Stewardship Science Academic Alliances Program of DOE’s National Nuclear Security Administration (NNSA).
Unless otherwise indicated, scholarly articles published by Duke faculty members are made available here with a CC-BY-NC (Creative Commons Attribution Non-Commercial) license, as enabled by the Duke Open Access Policy. If you wish to use the materials in ways not already permitted under CC-BY-NC, please consult the copyright owner. Other materials are made available here through the author’s grant of a non-exclusive license to make their work openly accessible.