Ponente
Descripción
Decay spectroscopy experiments aim at a detailed study of the decay mechanisms in the most exotic nuclear species at reach at FAIR, with the measurements of decay half-lives, competing decay modes, and isomeric state identification. For the experimental program conducted by the DESPEC collaboration, nuclides isolated by the FRS are stopped in the AIDA active implanter which is based on Si DSSSD detectors. Its role is to provide temporal and positional information on the implantations as well as the subsequent decays (α or β), while providing rough energy deposition information to distinguish between the decay processes. Its drawback is a limited time resolution of over 1 μs. For fast timing measurements and neutron detection, however, a time resolution better than 1 ns and the capability to detect and distinguish between ion implantations and subsequent decays are desired. To fulfill these requirements, a new Fibre IMPlanter (FIMP) was envisioned. The fundamental idea is to replace the DSSSD array with fibres made of a polystyrene-based scintillation material in thin PMMA cladding. The fibres are assembled in layers of orthogonally running mats, forming a fibre block. This design is based upon the assumption that β and α particles will hit at least one fibre in two consecutive layers so that complete position information is available. The mean β particle energy in the anticipated experiments will be in the order of 1 MeV, while the maximum deposited energy may go up to 10 MeV. For α particles the stopping power is larger, so they can be easily distinguished from β particles by their energy deposition in each fibre. Implanted ions produce traces through the fibre layers ending with a Bragg peak at the implantation position. For very heavy ions, the thickness required to stop all interesting species is just under 1 cm. A small-scale FIMP prototype with custom front-end readout electronics and a mechanical construction paradigm suitable for scaling up to the planned full size has been constructed. The fibres of a 12 mm thick
block are read out by 192 SiPMs arranged in lines of 16, which cover the side faces of the block and form three rings at different implantation depths. The resulting high granularity allows FIMP to sustain a high count rate, making it feasible to study several species at the same time. The SiPMs, their corresponding preamplifiers, and the fibre block itself are mounted inside a light-tight 3D-printed plastic enclosure which enables their precise relative positioning. The electronics make use of a resistive multiplexing matrix to reduce the required number of readout channels. Time and energy information is extracted from the analog SiPM signals using discrete implementations of constant fraction discriminators and time over threshold circuits, respectively. These produce differential signals that are subsequently sampled and processed by the ClockTDC system, and are constructed in a modular fashion in conjunction with a system control board, allowing for further detector developments. The detector system has recently been tested in combination with gammaray detectors for β-delayed γ correlations using a 100Mo beam at the GSI/FAIR facility, showing good performance. The design and preliminary results will be presented.
