Reactions with radioactive beams and development of scintillator-based detector systems
Abstract
An experiment on elastic scattering of 15 C on 208 Pb at an energy of 65 MeVwas performed at ISOLDE (CERN) exploiting the advantages of the ISOL te-chinique. The measurement showed in increase of the reaction cross section to3035 mb with respect to 12 C, confirming the results obtained at 80 MeV/u. Mea-surements to characterise and develop detector modules for the CALIFA setupwas performed for the R 3 B experiment at FAIR. Light output characteristics of478 detector modules of the CALIFA Barrel section were measured as a partthis work in order to investigate the correlation between resolution and non-uniformity. For this set of crystals the average resolution was found to be 5.2%(FWHM) at E γ = 1275 keV. Further investigations also done in this work showthat the inhomogeneity in the Tl dopant distribution contributes ∼0.5%, andthe noise in the read-out chain with .0.1% to that number. The most importantcontribution to variations in the resolution was found to be from non-uniformlight collection due to the geometry of the modules. The APD light read-outsensors were also investigated and found to be stable below 24.8 ◦ C using a gaincorrection algorithm. Energy add-back and light cross-talk were investigated.It was found that a closest-neighbor add-back algorithm recovers 14.7% of theevents for E γ = 662 keV and 65% of the events for E γ = 1460 keV, while thelight cross-talk contributes .0.03% to the photo peak. The attenuation lengthof the emission light of the scintillators was also determined and found to be34.6 ± 4.5 cm. In addition the micro facet distribution for a polished and alapped sample was measured using atomic force microscopy to produce look-uptables for GEANT4 simulations of light transport. Simulations of light outputnon-uniformity were performed for different configurations of lapped surfacesof a CALIFA detector module. The simulations reproduced the general trendof the measurement where the non-uniformity decreased with increasing lappedarea, although the exact values for the non-uniformity were not reproduced. Asensitivity test for the simulated light-output non-uniformity with respect todifferent input parameters was also performed. The non-uniformity was foundto be most sensitive to the reflectivity of the reflector foil while the sensitivityto the other parameters was less prominent.