Reduction of the molecular background in an atomic tritium setup using different shroud configurations

The investigation of the tritium β-decay spectrum at its endpoint is a direct way to measure the neutrino mass. Using molecular tritium reduces the achievable sensitivity by a broadening due to rotational and vibrational excitations of the 3HeT+ daughter molecule. The use of atomic tritium overcomes this fundamental limitation.

After a commissioning phase with inactive hydrogen, the "Beam for an Atomic Tritium Experiment" setup at Tritium Laboratory Karls-ruhe is going to demonstrate the production of atomic tritium. To dissociate the hydrogen molecules, a commercially available dissociation device, the tectra H-flux atomic hydrogen source, is used. Investigating the beam composition is done by a HIDEN DLS10 quadrupole mass spectrometer (QMS) equipped with a cross-beam ion source.

Previous results show that recombination by wall contacts produces a major molecular background. To prevent recombined molecules from reaching the QMS beam shaping skimmers and a shroud are indispensable. The latter is an actively pumped tube around the QMS. In this, two opposite holes act as a skimmer trimming the beam to the size of the QMS entrance aperture. ... mehrMolecules recombined inside the QMS are pumped away.

This talk presents the results investigating the reduction of the molecular background using different shroud configurations.