Abstract
The components, working principle and characteristics of FATIMA (FAst TIMing Array), a fast-timing detector system for DESPEC at FAIR, are described. The core system includes 36 LaBr3(Ce) scintillator detectors, a mounting frame for the DESPEC station and a VME-based fast-timing data acquisition system. The current electronic timing circuit is based on V812 constant fraction discriminators and V1290 time-to-digital converters. Gamma-ray energies are measured using V1751 digitisers. Characteristics of the core FATIMA system including efficiency, energy, and coincidence resolving time, as well as limitations, are discussed on the basis of test measurements performed in the S4 cave at GSI, Germany. The coincidence γ-γ time resolution for the prompt 60Co cascade is determined to be ∼320 ps full width at half maximum. The total full energy peak efficiency at 1 MeV for the 36 detector array in the DESPEC setup is 2.9%. The energy-dependent prompt response centroid curve with the current CFD/TDC combination is shown to be smooth; the centroid shift method can be applied for the measurement of half-lives below 200 ps. An overview of applications of the FATIMA detectors as an ancilliary system in combination with other detector arrays during recent years is given. Data on the operation of the detectors in the presence of magnetic fields are presented.
Highlights
The DESPEC (DEcay SPECtroscopy) experiment [1,2,3] as part of the NuSTAR project [4,5] for FAIR (Facility for Antiproton and Ion Research) [6] is designed to exploit the new possibilities FAIR will provide in terms of studying exotic nuclides at high beam intensities that are not possible anywhere else
The system is designed to work as part of the DESPEC station of FAIR in combination with AIDA [9] or a similar position sensitive implantation device, and other detector systems, like DEGAS [21]
The time difference spectrum prompt resolution we observe by using the digital constant fraction discriminators (CFDs) algorithm provided by the CAEN firmware is comparable with analogue to amplitude converters (TACs), but the actual measurement resolution we found to be around 64 ps in the least significant bit
Summary
The DESPEC (DEcay SPECtroscopy) experiment [1,2,3] as part of the NuSTAR project [4,5] for FAIR (Facility for Antiproton and Ion Research) [6] is designed to exploit the new possibilities FAIR will provide in terms of studying exotic nuclides at high beam intensities that are not possible anywhere else. FATIMA (FAst TIMing Array) is the detector system of the DESPEC experiment designed to measure lifetimes of excited nuclear states via the method of delayed coincidence electronic fast timing. This experimental technique has come to the. In combination with a fast plastic detector sandwiched with AIDA, the β−γ coincidence timing method can be applied, as introduced by Mach et al [14] and extensively used since the 1990s, e.g. at the ISOLDE facility at CERN [15] This technique is especially well suited for decay experiments of exotic nuclei, as the efficiency is typically higher than in γ-γ measurements.
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