Neutron elastic-scattering angular distributions were measured at beam energies of 11.9 and 16.9 MeV on 40,48 Ca targets. These data plus other elastic-scattering measurements, total and reaction cross sections measurements, (e, e ′ p) data, and single-particle energies for magic and doubly magic nuclei have been analyzed in the dispersive optical model (DOM) generating nucleon self-energies (optical-model potentials) which can be related, via the many-body Dyson equation, to spectroscopioc factors and occupation probabilities. It is found that for stable nuclei with N ≥ Z, the imaginary surface potential for protons exhibits a strong dependence on the neutron-proton asymmetry. This result leads to a more modest dependence of the spectroscopic factors on asymmetry. The measured data and the DOM analysis of all considered nuclei clearly demonstrates that the neutron imaginary surface potential displays very little dependence on the neutron-proton asymmetry for nuclei near stability (N ≥ Z).
The MajoranaDemonstratorwill search for the neutrinoless double-beta(ββ0ν)decay of the isotopeGe with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate that the neutrino is its own antiparticle, demonstrate that lepton number is not conserved, and provide information on the absolute mass scale of the neutrino. The Demonstratoris being assembled at the 4850-foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be situated in a low-background environment and surrounded by passive and active shielding. Here we describe the science goals of the Demonstratorand the details of its design.
Background: Double-beta decay is a rare nuclear process in which two neutrons in the nucleus are converted to two protons with the emission of two electrons and two electron anti-neutrinos. Purpose: We measured the half life of the two-neutrino double-beta decay of 150 Nd to excited final states of 150 Sm by detecting the de-excitation gamma rays of the daughter nucleus. Method: This study yields the first detection of the coincidence gamma rays from the 0 + 1 excited state of 150 Sm. These gamma rays have energies of 333.97 keV and 406.52 keV, and are emitted in coincidence through a 0 + 1 →2 + 1 →0 + gs transition. Results: The enriched Nd2O3 sample consisted of 40.13 g 150 Nd and was observed for 642.8 days at the Kimballton Underground Research Facility, producing 21.6 net events in the region of interest. This count rate gives a half life of T 1/2 = (1.07 +0.45 −0.25 (stat) ± 0.07(syst.)) × 10 20 years. The effective nuclear matrix element was found to be 0.0465 +0.0098 −0.0054. Finally, lower limits were obtained for decays to higher excited final states. Conclusions: Our half-life measurement agrees within uncertainties with another recent measurement in which no coincidence was employed. Our nuclear matrix element calculation may have an impact on a recent neutrinoless double-beta decay nuclear matrix element calculation which implies the decay to the first excited state in 150 Sm is favored over that to the ground state.
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