A.A. Hahn

Experimental beta-spectra from 239Pu and 235U thermal neutron fission products and their correlated antineutrino spectra☆

Abstract The beta spectrum from 239Pu thermal neutron fission fragments was measured on-line with a magnetic spectrometer in the energy interval Eβ = 1.5 to 8.0 MeV. The beta spectrum was converted into the correlated electron antineutrino spectrum taking into account the Z distribution of the fission products. With a total uncertainty for this ν e-spectrum of 4.7, 5.2 and 11% at 3.0, 0.5 and 7.0 MeV, respectively, a basis for neutrino experiments at nuclear power reactors is given. The previously obtained 235U antineutrino spectrum was refined by this improved conversion method.

An experimental study of muonic X-ray transitions in mercury isotopes☆

Abstract Muonic X-ray spectra have been measured for 198–202, 204Hg. These data have been interpreted in terms of a two parameter Fermi distribution for the charge density. We have interred the spectroscopic quadrupole moments (Qs) of some of the 2+ nuclear states. For 199Hg we have determined the spectroscopic quadrupole moments of the first two excited states and the B(E2) connecting these states to the ground state. For 201Hg the ground state quadrupole moment has been obtained as well as several other E2 moments but the interpretation of the data has been hampered by a possible incomplete knowledge of the nuclear scheme of this nucleus. The muonic isotope shifts have been measured and interpreted in terms of σRk and are compared to electronic X-ray and optical isotope shift measurements.

New limits on oscillation parameters for electron antineutrinos

Abstract The positron spectrum from the reaction ν e + p → e + + n has been measured at L=37.9 from the core of the Gosgen power reactor to search for neutrino oscillations of the type ν e ↔ x in the low mass parameter range. The results are consistent with the no neutrino oscillation hypothesis. Upper limits of δm 2 ⪕ 0.016 eV 2 (90% c.l..) for full mixing, and sin 2 2θ⪕0.17 (90% c.l.) in the limit of large mass parameters were determined. For the ratio of the integrated experimental yield to that predicted for the case of no oscillations a value of 1.05 ± 0.02 (statistical) ± 0.05 (systematic; 68% c.l.) was obtained.

Experimental study of neutrino oscillations at a fission reactor

Abstract The electron-antineutrino spectrum has been measured at a position 8.75 m from the “point-like” core of the ILL 235 U fission reactor, using the reaction ν e + p → e + + n. Positrons and neutrons were detected in coincidence by means of a low-background liquid scintillator and a 3 He detector system. The observed neutron correlated positron spectrum is consistent with theoretical predictions assuming no neutrino oscillations. Upper limits for the oscillation parameter are presented.

Absolute measurement of the beta spectrum from 235U fission as a basis for reactor antineutrino experiments

The beta spectrum from fission products in thermal-neutron induced fission of 235U has been measured on line at the ILL reactor with a magnetic spectrometer. In the energy range from Eβ = 2.0 to 7.5 MeV the spectrum was determined per fission with an accuracy of 5%. The experimental electron spectrum was converted to the corresponding electron antineutrino spectrum to form a basis for the study of antineutrino induced reactions at reactors.

An experimental limit on production of axions in a fission reactor

Abstract We report on an experiment conducted at the ILL reactor aimed at searching for coincident gamma-ray events from axion decay. No such events are seen and our results are interpreted, using the calculations by Donnelly et al., as an upper limit of the axion mass of 280 keV.

Nuclear charge parameters and quadrupole moment in 105Pd from muonic X-rays

Abstract The K and L X-rays of muonic 105 Pd were measured and the radial parameters of the charge distribution in 105 Pd were derived. Based on 2p state hyperfine splitting, the spectroscopic quadrupole moment was determined to be Q s = 0.660(11) e · b.

Experimental determination of the relativistic fine structure splitting in a pionic atom

Abstract Using a high-resolution crystal spectrometer, we have measured the energy splitting of the pionic 5g-4f and 5f-4d transitions in Ti. The observed fine structure splitting agrees, within experimental error of 3%, with the splitting arising from the calculated relativistic term and other small corrections for spinless particles.