Neutron-deuteron analyzing power data at 19.0 MeV
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2010-02-23
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Measurements of neutron-deuteron (n-d) analyzing power Ay(θ) at En=19.0 MeV are reported at 16 angles from θc.m.=46.7 to 152.0°. The objective of the experiment is to better characterize the discrepancies between n-d data and the predictions of three-nucleon calculations for neutron energies above 16.0 MeV. The experiment used a shielded neutron source, which produced polarized neutrons via the H2(d-,n-)He3 reaction, a deuterated liquid scintillator center detector (CD) and liquid-scintillator neutron side detectors. A coincidence between the CD and the side detectors isolated the elastic-scattering events. The CD pulse height spectrum associated with each side detector was sorted by using pulse-shape discrimination, time-of-flight techniques, and by removing accidental coincidences. A Monte Carlo computer simulation of the experiment accounted for effects due to finite geometry, multiple scattering, and CD edge effects. The resulting high-precision data (with absolute uncertainties ranging from 0.0022 to 0.0132) have a somewhat lower discrepancy with the predictions of three-body calculations, as compared to those found at lower energies. © 2010 The American Physical Society.
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Weisel, GJ, W Tornow, BJ Crowe, AS Crowell, JH Esterline, CR Howell, JH Kelley, RA Macri, et al. (2010). Neutron-deuteron analyzing power data at 19.0 MeV. Physical Review C - Nuclear Physics, 81(2). p. 24003. 10.1103/PhysRevC.81.024003 Retrieved from https://hdl.handle.net/10161/4259.
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Scholars@Duke
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).
Alex Crowell
Calvin R. Howell
Professor Howell’s research is in the area of experimental nuclear physics with emphasis on the quantum chromodynamics (QCD) description of low-energy nuclear phenomena, including structure properties of nucleons and nuclei and reaction dynamics in few-nucleon systems. The macroscopic properties of nucleon structure and the residual strong nuclear force between neutrons and protons in nuclei emerge from QCD at distances where the color interactions between quarks and gluons are strong. However, the details of the mechanisms that generate the strong nuclear force are not well understood. Effective field theories (EFT) and Lattice QCD calculations provide theoretical frames that connect low-energy nuclear phenomena to QCD. Professor Howell and collaborators are conducting experiments on few-nucleon systems that test predictions of ab-initio theory calculations for the purpose of providing insight about the QCD descriptions of low-energy nucleon interactions and structure. His current projects include measurements of the electromagnetic and spin-dependent structure properties of nucleons via Compton scattering on the proton and few-nucleon systems and studies of two- and three-nucleon interactions using few-nucleon reactions induced by photons and neutrons. In the coming years, a focus will be on investigating the neutron-neutron interaction in reactions and inside nuclei. In addition, his work includes applications of nuclear physics to national nuclear security, medical isotope production, and plant biology. Most of his research is carried out at the High Intensity Gamma-ray Source and the tandem laboratory at TUNL.
John H Kelley
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