The KArlsruhe TRItium Neutrino experiment, KATRIN, will make a model-independent measurement of the mass of the electron antineutrino in the quasi-degenerate regime (m1≈m2≈m3m1≈m2≈m3). It continues a series of tritium-based experiments, including Mainz and Troitsk, which established the present model-independent limit.

MIT Bates worked on two systems for this experiment, the Shield and Veto System and the Calibration System.

Shield and Veto System

The radiation shield consists of two nested cylindrical shells: a 3-cm thickness of lead that reduces the γ background by an estimated factor of 20, and an inner 1.27-cm thickness of oxygen-free, high-conductivity copper to block lead X-rays. It is surrounded by a veto system to tag incoming muons: a four-panel barrel with its downstream end partially covered by two semicircular endcap panels. Each curved, 1-cm-thick panel is made of St. Gobain Bicron-408 plastic scintillator wrapped in Gore Diffuse Reflector Product, with an outer layer of adhesive-backed aluminum foil. The whole assembly is 38 cm in outer diameter and 106.3 cm in length. Embedded single-clad St. Gobain wavelength-shifting (WLS) fibers collect scintillation light and transport it to photon detectors. There are three WLS fibers in each of the four long panels and two in each of the two endcap panels; the fibers are bent into U shapes and read out at both ends. Outside the scintillator panels, each WLS fiber end couples to a clear plastic optical fiber, which has a longer attenuation length.

Calibration systems

Two systems, one providing γs and one providing photoelectrons with adjustable energies, calibrate the detector׳s response to incident particles. Monitoring the photocurrent of the latter source also allows measurements of the detector efficiency.