Discovery of an Exceptionally Strong β -Decay Transition of F20 and Implications for the Fate of Intermediate-Mass Stars

A significant fraction of stars between 7 and 11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on ^{20}Ne in the degenerate oxygen-neon stellar core. However, because of the unknown strength of the transition between the ground states of ^{20}Ne and ^{20}F, it has not previously been possible to fully constrain the rate. By measuring the transition, we establish that its strength is exceptionally large and that it enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupte…

Discovery of an Exceptionally Strong β -Decay Transition of $^{20}$F and Implications for the Fate of Intermediate-Mass Stars

A significant fraction of stars between 7-11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on $^{20}$Ne in the degenerate oxygen-neon stellar core. However, due to the unknown strength of the transition between the ground states of $^{20}$Ne and $^{20}$F, it has not previously been possible to fully constrain the rate. By measuring the transition, we have established that its strength is exceptionally large and enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted b…

The Electric Formfactor of the Neutron Determined by Quasielastic Scattering of Longitudinally Polarized Electrons from 3He and 2D

The recent availability of polarized electron beams at electron accelerator laboratories adds another technique to probing the electromagnetic structure of nuclear matter [1]. The present paper discusses the application of polarized electron scattering to the determination of the electric formfactor of the neutron. Its value at medium energies is only poorly known hitherto. Electron scattering is dominated by interaction with the neutron magnetic moment. Therefore the contribution of the charge distribution to the scattering cross section is scarcely detectable in case of unpolarized collision partners. The elastic scattering of longitudinally polarized electrons from a polarized neutron ta…

First measurement of the electric formfactor of the neutron in the exclusive quasielastic scattering of polarized electrons from polarized 3He

Abstract A first measurement of the asymmetry in quasielastic scattering of longitudinally polarized electrons from a polarized 3 He gas target in coincidence with the knocked out neutron is reported. This measurement was made feasible by the cw beam of the 855 MeV Mainz Microtron MAMI. It allows a determination of the electric formfactor of the neutron G E n independent of binding effects to first order. At Q 2 =0.31 ( GeV /c) 2 two asymmetries A ∥ ( S He ∥ q ) and A ⊥ ( S He ⊥ q ) have been measured giving A ∥ =(−7.40±0.73)% and A ⊥ =(0.89±0.30)% . The ratio A ⊥ / A ∥ is independent of the absolute value of the electron and target polarization and yields G E n =0.035±0.012±0.005.

Discovery of an Exceptionally Strong β -Decay Transition of F 20 and Implications for the Fate of Intermediate-Mass Stars

Determination of the neutron electric form factor from the reaction 3 He(e,e'n) at medium momentum transfer

The electric form factor of the neutron GEn has been determined in double polarized exclusive 3He(e,e'n) scattering in quasi–elastic kinematics by measuring asymmetries A⊥, A∥ of the cross section with respect to helicity reversal of the electron, with the nuclear spin being oriented perpendicular to the momentum transfer q in case of A⊥ and parallel in case of A∥. The experiment was performed at the 855 MeV c. w. microtron MAMI at Mainz. The degree of polarization of the electron beam and of the gaseous 3He target were each about 50%. Scattered electrons and neutrons were detected in coincidence by detector arrays covering large solid angles. Quasi–elastic scattering events were reconstruc…