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Stored and Cooled Ions Division
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THe-TRAP Project

Neutrino mass

The β-decay of 3H (Tritium) to 3He is the most promising candidate for the direct mass determination of the neutrino. A mass larger than zero will modify the shape of the energy spectrum of the emitted β-electron near the high-energy endpoint as illustrated in Fig. 2.1.


Emitted electron energy spectrum E_kin of β-decay of tritium.
Fig. 2.1: Emitted electron energy spectrum Ekin of β-decay of tritium. E0 is equal to the kinetic energy, assuming that neutrinos have no mass, i.e. m(νe) = 0. Near the endpoint, the effect of the neutrino mass on the line shape becomes most visible. Only a fraction of 2⋅10-13 of all emitted e- has an energy of E0 - 1 eV.

The 3H-to-3He mass difference yields the maximum kinetic energy E0 of the released β-decay electron and thus provides information for the analysis of the β-spectrum (see Figure 2.1). In 2016, KATRIN is expected to start data acquisition on the β-spectrum, with the aim of an unprecedented sensitivity of m(νe) < 0.2 eV/c2. This will also lead to a value for E0.
By taking the recoil and excitation of the daughter core into account, E0 can be calculated and compared with the spectrum, which will be a test of systematic errors for KATRIN.

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In order to meet also the safety and the precision requirements, great care has been taken in the preparation of the tritium laboratory at MPIK. Foremostly tritium is a radioactive gas and thus its handling requires special care. Together with the authority in Karlsruhe and the radiation safety group at MPIK, a detailed security policy was developed, which was reviewed and approved by the service company DEKRA. The concept (see figure 2.2) consists of a separate ventilation system, an extra encapsulation of the experiment, glove boxes in the experiment area and an alarm system for a possible tritium spill.


Scheme of the tritium safety system.
Fig. 2.2: Scheme of the tritium safety system. Visible are the upper laboratory, in which racks with the most electronics are located (room 2), the magnet room with the magnet, which contains the Penning trap (room 1) and a second room (Room 3), which serves as cold reservoir for temperature stabilization in room 1. The volume in which tritium is contained is framed in orange and blue. At the tritium monitoring area (green), an alarm system (yellow) and powerful fans are connected.