Characterizing the SOFIA/ANDES TwinMUSIC

Abstract

Preliminary values for the resolutions of various figures of merit have been deduced by the SOFIA TwinMUSIC [1] for the spectra of isotopes obtained from the fission of U. The energy-loss resolution was measured to be σΔE E = 0.34% with P25 gas (Fig. 1). This leads to a charge resolution of σZ1,2 = 0.23± 0.01 for the measurements in 1 2 of the TwinMUSIC and σZ1+2 = 0.31±0.02 for the sum of both. The steep falloff of Δt,10−90% ≈ 150ps of the drift times close to the cathode measured for single anodes yields a corresponding resolution of the straight-line fit to a track through the active volume of σdt,fit = (268± 40)ps (Fig. 2). For the electrical field settings applied the measured drift velocity is well reproduced by Magboltz simulations. After fine adjustment of the drift-times with the help of an adjacent MWPC, a position resolution for the single anode of σx,PB = (28±11)μm and σx,FF = (47±13)μm for the primary beam and fission fragments, respectively, can be deduced (Fig. 3). Consequently, the angular distribution of the fragments of ≈ 40mrad could be measured with a precision of σΘ,FF = (0.13± 0.10)mrad by eventwise tracking. The analysis of the data is still ongoing, further refinements on the achieved resolutions are to be expected. Isotopic mass yields have been be deduced and published elsewhere [2]. Changes in the design of the TwinMUSIC detector system are ongoing and will allow for an even better charge, position and angular resolution. We are aiming for a full 3D tracking operation with rates of 1 − 2 MHz with a non-triggered DAQ. The potential of a low-pressure operation (0.2 − 0.3atm) and the application of other, ’faster’ gas mixtures will be tested too. The next physics run is already scheduled 2014 at CaveC looking into more details of the isotopic mass distributions. In the far future, a more complete set of measurements will be performed in the context of RB (Reaction studies with Relativistic Radioactive Beams) at the FAIR (Facility for Antiproton and Ion Research) project at GSI/Darmstadt. Dedicated detector developments will be performed for those endeavors which foster similar developments e.g. for the instrumentation of the SuperFRS.