A CsI(Tl) hodoscope on CSHINE for Bremsstrahlung γ-rays in heavy ion reactions

Bremsstrahlung γ production in heavy ion reactions at Fermi energies carries important physical information including the nuclear symmetry energy at supra-saturation densities. In order to detect the high energy Bremsstrahlung γ rays, a hodoscope consisting of 15 CsI(Tl) crystals read out by photo multiplier tubes has been built, tested and operated in experiment. The resolution, efficiency and linear response of the units to γ rays have been studied using radioactive source and (p,γ) reactions. The inherent energy resolution of 1.6%+2%/Eγ1/2 is obtained. Reconstruction method has been established through Geant 4 simulations, reproducing the experimental results where comparison can be made. Using the reconstruction method developed, the whole efficiency of the hodoscope is about 2.6×10−4 against the 4π emissions at the target position, exhibiting insignificant dependence on the energy of incident γ rays above 20 MeV. The hodoscope is operated in the experiment of 86Kr+124Sn at 25 MeV/u, and a full γ energy spectrum up to 80 MeV has been obtained.