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Wyświetlanie 1-10 z 56
Tytuł:
Few-nucleon research at TUNL : probing two- and three-nucleon interactions with neutrons
Autorzy:
Howell, C. R.
Witała, Henryk
Tornow, W.
Opis:
The central goal of few-nucleon research at the Triangle Universities Nuclear Laboratory (TUNL) is to perform measurements that contribute to advancing ab-initio calculations of nuclear structure and reactions. The program aims include evaluating theoretical treatments of few-nucleon reaction dynamics through strategically comparing theory predictions to data, determining properties of the neutron-neutron interaction that are not accessible in two-nucleon reactions, and searching for evidence of longrange features of three-nucleon interactions, e.g., spin and isospin dependence. This paper will review studies of three- and four-nucleon systems at TUNL conducted using unpolarized and polarized neutron beams. Measurements of neutron-induced reactions performed by groups at TUNL over the last six years are described in comparison with theory predictions. The results are discussed in the context of the program goals stated above. Measurements of vector analyzing powers for elastic scattering in A=3 and A=4 systems, differential cross sections for neutron-deuteron elastic scattering and neutrondeuteron breakup in several final-state configurations are described. The findings from these studies and plans for the coming three years are presented in the context of worldwide activities in this front, in particular, research presented in this session.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Inne
Tytuł:
Neutron-deuteron analyzing power data at $E_{n} = 22.5$ MeV
Autorzy:
Esterline, J. H.
Hale, G. M.
Weisel, G. J.
O'Malley, P. D.
Witała, Henryk
Tompkins, J. R.
Howell, C. R.
Crowell, A. S.
Tornow, W.
Opis:
We present measurements of n-d analyzing power, $A_{y}\left ( \theta \right )$, at $E_{n} = 22.5$ MeV. The experiment uses a shielded neutron source which produced polarized neutrons via the $^{2}H\left ( \vec{d},\vec{n} \right )^{3}He$ reaction. It also uses a deuterated liquid-scintillator center detector and six pairs of liquid-scintillator neutron side detectors. Elastic neutron scattering events are identified by using time-of-flight techniques and by setting a window in the center detector pulse-height spectrum. The beam polarization is monitored by using a high-pressure helium gas cell and an additional pair of liquid-scintillator side detectors. The $n-d A_{y}\left ( \theta \right )$ data were corrected for finite-geometry and multiple-scattering effects using a Monte Carlo simulation of the experiment. The 22.5-MeV data demonstrate that the three-nucleon analyzing power puzzle also exists at this energy. They show a significant discrepancy with predictions of high-precision nucleon-nucleon potentials alone or combined with Tucscon-Melbourne or Urbana IX three-nucleon forces, as well as currently available effective-field theory based potentials of next-to-next-to-next-to-leading order.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
Cross-section measurements of ^{2}H(n,np)n in symmetric star configurations
Autorzy:
Crowell, A. S.
Howell, C. R.
Cumberbatch, L. C.
Pedroni, R. S.
Clegg, T. B.
Esterline, J. H.
Witała, Henryk
Tajima, S.
Crowe, B. J.
Fallin, B.
Markoff, D. M.
Couture, A. H.
Opis:
Cross-section measurements have been made at 16 and 19 MeV in two exit-channel configurations of neutron-deuteron breakup: the space star and coplanar star. In this kinematically complete measurement, the outgoing proton and one of the neutrons were detected in coincidence and their energies were determined via time-of-flight techniques. Monte Carlo simulations based on rigorous three-nucleon Faddeev calculations using the charge-dependent-Bonn (CD-Bonn) nucleon-nucleon potential were used to compare the experimental results with theory. Large discrepancies between data and theory were found in both breakup configurations measured at both energies, suggesting deficiencies in current theoretical treatment of three-nucleon forces or in present knowledge of the neutron-neutron ^{1}S_{0} force.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Tytuł:
Measurement of the $^{1}S_{0}$ neutron-neutron effective range in neutron-deuteron breakup
Autorzy:
Malone, C. R.
Crowell, A. S.
Witała, Henryk
Tornow, W.
Ticehurst, D. R.
Fallin, B. A.
Howell, C. R.
Crowe, B. J.
Cumberbatch, L. C.
Malone, R. C.
Markoff, D. M.
Friesen, F. Q. L.
Opis:
We report the most precise determination of the $^{1}S_{0}$ neutron-neutron effective range parameter $(r_{nn})$ from neutron-neutron quasifree scattering in neutron-deuteron breakup. The experiment setup utilized a collimated beam of 15.5 MeV neutrons and an array of eight neutron detectors positioned at angles sensitive to several quasifree scattering kinematic configurations. The two neutrons emitted from the breakup reaction were detected in coincidence and time-of-flight techniques were used to determine their energies. The beam-target luminosity was measured in-situ with the yields from neutron-deuteron elastic scattering. Rigorous Faddeev-type calculations using the CD Bonn nucleon-nucleon potential were fit to our cross-section data to determine the value of $r_{nn}$. The analysis was repeated using a semilocal momentum-space regularized $N^{4}LO^{+}$ chiral interaction potential. We obtained values of $r_{nn}=2.86 \pm 0.01 (stat) \pm 0.10 (sys)$ fm and $r_{nn}=2.87 \pm 0.01 (stat) \pm 0.10 (sys)$ fm using the CD Bonn and $N^{4}LO^{+}$ potentials, respectively. Our results are consistent with charge symmetry and previously reported values of $r_{nn}$.
Dostawca treści:
Repozytorium Uniwersytetu Jagiellońskiego
Artykuł
Wyświetlanie 1-10 z 56

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