Ernst-Wilhelm Otten

Status and perspectives of the Mainz neutrino mass experiment

Abstract The Mainz measurement in 1994 is discussed in the view of the problem of “negative m ν 2 ” obtained in the analysis for larger energy intervals below the endpoint of the β spectrum. A possible explanation due to a roughening transition of the T 2 film is given. The very recent improvement of the Mainz setup and a first 4 weeks measurement is presented. An outlook to the perspectives of the present setup and into the future is given.

Precision measurement of the conversion electron spectrum of83m Kr with a solenoid retarding spectrometer

This paper reports on precision measurements of conversion lines in the decay of83mKr with nuclear transition energies of 32.1 keV and 9.4 keV, respectively. The spectra were taken from a submonolayer surface of83mKr frozen onto a cold backing, using the new Mainz solenoid retarding spectrometer. The high luminosity and resolution of this instrument enables the observation of all allowed conversion lines up to theN-shell and to fully separate the elastic component from inelastic satellites. The combined analysis of the data yields the transition energiesEy=32151.5±1.1 eV and 9405.9±0.8 eV, respectively. The experiment served also to pilot the application of this spectrometer to the question of a finite neutrino rest mass, searched for in theβ-decay spectrum of tritium and to problems in precision electron spectroscopy in general.

Structural Stability of Solid Deuterium Films

The wetting behavior of quenched-condensed solid D2 films has been investigated by means of light scattering. On the substrates used here (graphite and aluminum) molecular deuterium displays triple point wetting and hence dewets in the solid state, provided the temperature is high enough that thermally activated diffusion processes can take place. This manifests itself in a coarse-graining of the D2 film. In order to avoid this process and to obtain complete wetting of solid D2 we have modified the adsorbate-substrate interaction potential by preplating the substrates with thin inert layers of Ne, Ar, CH4 or C2H6. The predicted change in the wetting properties was not observed, however, suggesting that the existing picture of triple point wetting of van der Waals systems is not complete. The implications of these results for a neutrino mass experiment where quenched-condensed molecular tritium films are used as a source are discussed.

Measurement of the asymmetries in 3

Abstract.The electron target asymmetries A || and A⊥ with target spin parallel and perpendicular to the momentum transfer

\overrightarrow{\sf He}

\ensuremath{\boldsymbol{q}}

(¯e, e′p)d and 3

were measured for both the two- and three-body breakup of 3He in the 3

\overrightarrow{\sf He}

\overrightarrow{\rm He}

(¯e, e′p)np

(¯e, e’p)-reaction. Polarized electrons were scattered off polarized 3He in the quasielastic regime in parallel kinematics with the scattered electron and the knocked-out proton detected using the Three-Spectrometer Facility at MAMI. The results are compared to Faddeev calculations which take into account Final-State Interactions as well as Meson Exchange Currents. The experiment confirms the prediction of a large effect of Final-State Interactions in the asymmetry of the three-body breakup and of an almost negligible one for the two-body breakup.The electron target asymmetries A || and A ⊥ with target spin parallel and perpendicular to the momentum transfer were measured for both the two- and three-body breakup of 3 He in the 3 (¯ e , e’p )-reaction. Polarized electrons were scattered off polarized 3 He in the quasielastic regime in parallel kinematics with the scattered electron and the knocked-out proton detected using the Three-Spectrometer Facility at MAMI. The results are compared to Faddeev calculations which take into account Final-State Interactions as well as Meson Exchange Currents. The experiment confirms the prediction of a large effect of Final-State Interactions in the asymmetry of the three-body breakup and of an almost negligible one for the two-body breakup.

A Scheme for Measuring the Neutrino Rest Mass from the β-Decay of Stored Tritium Atoms Using a Solenoid Retardation Spectrometer

A new type of electron spectrometer is under construction at Mainz University that allows a measurement of the β-spectrum of tritium with high resolution and transmission in order to determine the neutrino rest mass. It consists of a source that contains atomic tritium, trapped in a high magnetic field, and a solenoid retarding spectrometer.

Stability of solid T2 films

Abstract Films of molecular tritium, physisorbed on a cold substrate, have been investigated by means of ellipsometry. A significant effect of the radioactive decay processes on the desorption kinetics and the low temperature stability of these films is not observed.