A CsI hodoscope on CSHINE for Bremsstrahlung {\gamma}-rays in Heavy Ion Reactions

TL;DR

This paper presents the development, testing, and application of a CsI(Tl) hodoscope for detecting high-energy Bremsstrahlung gamma rays in heavy ion reactions, providing insights into nuclear symmetry energy at high densities.

Contribution

The paper introduces a new CsI(Tl) hodoscope with established reconstruction methods and demonstrates its effectiveness in measuring gamma-ray spectra in heavy ion collision experiments.

Findings

Energy resolution of 1.6%+2%/Eγ^{1/2} achieved.

Hodoscope efficiency is approximately 2.6×10^{-4} for 4π emissions.

Full gamma spectrum up to 80 MeV obtained in experiment.

Abstract

Bremsstrahlung $\gamma$ 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 $\gamma$ rays, a hodoscope consisting of 15 CsI(Tl) crystal read out by photo multiplier tubes has been built, tested and operated in experiment. The resolution, efficiency and linear response of the units to $\gamma$ rays have been studied using radioactive source and $({\rm p},\gamma)$ reactions. The inherent energy resolution of $1.6\%+2\%/E_{\gamma}^{1/2}$ 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 $2.6\times 10^{-4}$ against the $4\pi$ emissions at the target position, exhibiting insignificant dependence on the energy of incident $\gamma$ rays above 20 MeV. The hodoscope is operated in the experiment of $^{86}$Kr + $^{124}$Sn at 25 MeV/u, and a full $\gamma$ energy spectrum up to 80 MeV has been obtained.