6The beta decay of molecular tritium currently provides the highest sensitivity in laboratory-based
The focal-plane detector system for the KArlsruhe TRItium Neutrino (KATRIN) experiment consists of a multi-pixel silicon p-i-n-diode array, custom readout electronics, two superconducting solenoid magnets, an ultra high-vacuum system, a high-vacuum system, calibration and monitoring devices, a scintillating veto, and a custom data-acquisition system. It is designed to detect the low-energy electrons selected by the KATRIN main spectrometer. We describe the system and summarize its performance after its final installation.Comment: 28 pages. Two figures revised for clarity. Final version published in Nucl. Inst. Meth.
The KATRIN experiment will probe the neutrino mass by measuring the β-electron energy spectrum near the endpoint of tritium β-decay. An integral energy analysis will be performed by an electro-static spectrometer ("Main Spectrometer"), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m 3 , and a complex inner electrode system with about 120 000 individual parts. The strong magnetic field that guides the β-electrons is provided by super-conducting solenoids at both ends of the spectrometer. Its influence on turbo-molecular pumps and vacuum gauges had to be considered. A system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter strips has been deployed and was tested during the commissioning of the spectrometer. In this paper the configuration, the commissioning with bake-out at 300 • C, and the performance of this system are presented in detail. The vacuum system has to maintain a pressure in the 10 −11 mbar range. It is demonstrated that the performance of the system is already close to these stringent functional requirements for the KATRIN experiment, which will start at the end of 2016.
Semiconductor detectors in general have a dead layer at their surfaces that is either a result of natural or induced passivation, or is formed during the process of making a contact. Charged particles passing through this region produce ionization that is incompletely collected and recorded, which leads to departures from the ideal in both energy deposition and resolution. The silicon p-i-n diode used in the KATRIN neutrinomass experiment has such a dead layer. We have constructed a detailed Monte Carlo model for the passage of electrons from vacuum into a silicon detector, and compared the measured energy spectra to the predicted ones for a range of energies from 12 to 20 keV. The comparison provides experimental evidence that a substantial fraction of the ionization produced in the "dead" layer evidently escapes by diffusion, with 46% being collected in the depletion zone and the balance being neutralized at the contact or by bulk recombination. The most elementary model of a thinner dead layer from which no charge is collected is strongly disfavored.
The Karlsruhe Tritium Neutrino Experiment (KATRIN) will detect tritium betadecay electrons that pass through its electromagnetic spectrometer with a highlysegmented monolithic silicon pin-diode focal-plane detector (FPD). This pin-diode array will be on a single piece of 500-µm-thick silicon, with contact between titanium nitride (TiN) coated detector pixels and front-end electronics made by spring-loaded pogo pins. The pogo pins will exert a total force of up to 50 N on the detector, deforming it and resulting in mechanical stress up to 50 MPa in the silicon bulk. We have evaluated a prototype pin-diode array with a pogo-pin connection scheme similar to the KATRIN FPD. We find that pogo pins make good electrical contact to TiN and observe no effects on detector resolution or reverse-bias leakage current which can be attributed to mechanical stress.The Karlsruhe Tritium Neutrino Experiment (KATRIN) is a direct, model-2 independent search for the absolute mass of the electron antineutrino [1]. The 3 highest energy electrons from the beta decay of molecular tritium (T 2 ) will be 4 selected by a MAC-E spectrometer [2] and tagged with a focal-plane detector 5 (FPD). The overall sensitivity to antineutrino mass depends critically on the 6 minimization of backgrounds, which can be achieved by placing the FPD in 7 extreme high vacuum (XHV) (p ∼ 10 −9 Pa) and avoiding materials with high 8 natural radioactivity near the FPD. These conditions constrain the design of 9 the FPD and preclude many standard detector construction materials and 10 techniques. Therefore we have developed a novel scheme to support and read 11 out the FPD. 12 2 The KATRIN FPD (Fig. 1) is a monolithic silicon pin-diode array manufac-13 tured by Canberra, Belgium. The n-type silicon substrate wafer is 500 µm 14 thick with a diameter of 114 mm. It is bare, with no housing or backing of any 15 kind. The entrance, or front side, is uniformly n ++ -doped with no segmenta-16 tion. The back side is p ++ -doped in 148 individual 44.1-mm 2 pixels arranged 17 in a circular dartboard pattern surrounded by a continuous guard ring. The 18 111 crystal orientation is perpendicular to the surface. The outermost pix-19 els extend to a diameter of 90 mm. A guard ring extends from a diameter of 20 90 mm out to 94 mm. The pixels and guard ring are covered with titanium ni-21 tride (TiN) for electrical contact to the front-end electronics. The guard ring 22 is to be held at signal reference potential to sink surface currents that might 23 otherwise flow between the outer pixels and regions of the surface held at bias 24 potential. Outside the guard ring there is a coating of TiN (but no doping) 25 from a diameter of 100 mm extending around the edge of the wafer to the n ++ 26 doping on the front side. The TiN on the front side extends a few mm from 27 the edge, but the front is otherwise unmetallized. This configuration allows 28 the bias potential on the front side to be applied via connections made on the 29 back side adjacent to signal connections. TiN was chosen as...
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