Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

HK: Fachverband Physik der Hadronen und Kerne

HK 69: Instrumentierung XIII

HK 69.8: Vortrag

Freitag, 19. März 2010, 15:45–16:00, HG ÜR 5

Development of a low neutron emission ²²⁸Th source for the calibration of GERDA — •Michal Tarka — Universitaet Zuerich

GERDA (GERmanium Detector Array) is a very-low background experiment under construction at LNGS (Laboratori Nazionali del Gran Sasso, 3400 m.w.e.) in Italy. It is designed to search for the neutrinoless double-β decay using an array of enriched ⁷⁶Ge detectors. A limit of T_1/2=15·10²⁵ y in Phase II of GERDA can be achieved by limiting the background rate to B ≤ 1·10⁻³ cts/(keV·kg·y). This requires a good understanding and suppression of the background produced by cosmic rays and natural radioactivity. Furthermore neutrons from spontaneous fission and (α,n) reactions in adjacent materials can contribute considerably to the background rate. ²²⁸Th has been established as a good calibration source candidate for GERDA due to its γ-emission in the region of interest around Q_ββ = 2.04 MeV. The calibration setup requires that the ²²⁸Th source is permanently installed in the setup during data taking in a parking position at 3.5 m above the germanium detector array. Monte Carlo simulations have shown that the γ-background from the calibration source located in its parking position can be suppressed by a Ta absorber. This work investigates the significance of the neutron background induced by (α,n) reactions within the intrinsic components of a commercialy available ²²⁸Th calibration source. Furthermore a new type of a ²²⁸Th source has been developed in order to reduce the n-rate approximately by two orders of magnitude compared to a commercial ²²⁸Th source.