Study Of Detector System For Intermediate-energy Coulomb Excitation Reactions At The External Target Facility Of HIRFL-CSR

Intermediate-energy Coulomb excitation reaction is one of the most important experimental methods to study the structures and properties of exotic nuclei which locate far away from the β-stable valley. The main subject of this thesis is to design and test the detectors which will be utilized in intermediate-energy Coulomb excitation experiments at the External Target Facility of HIRFL-CSR.As the reaction products are usually in excited states, the detection of the γ rays emitted from the excited products is very important, which makes the Gamma Ball detector one of the key detectors in intermediate-energy Coulomb excitation experiments. Detection efficiency is one of the most important indexes for those γ-ray detectors as well as an important input parameter in the experimental data analysis. One of the major work in this thesis is to study the detection efficiency of the Gamma-Ball detector. We have tested the detector, which was operated in Add-back mode, with the 60 Co source by coincident measurement and done a simulation with the GEANT4 software. The results obtained by the test and simulation are compared with each other and the differences between those two methods are discussed in the thesis.Another work of this thesis is to design and construct a new detector for identifying charged products after the reaction target at the External Target Facility. The previous one is a magnetic spectrometer, which is operated in Bρ-TOF-ΔE method. As the scattering angles of reaction products cannot be extracted with this magnetic spectrometer, the utilization of this magnetic spectrometer is limited in intermediate-energy Coulomb excitation experiments. Hence, a Cs I(Tl) telescope, which is based on the ΔE-E-Range method, is designed and constructed to solve this problem. This detector contains seven layers of Cs I(Tl) crystals with different thickness and the signals of each crystal are read out by 4 photomultiplier tubes at 4 corners. A Monte Carlo program, which is based on GEANT4, is used to study the performance of the detector. Two particle identification(PID) methods, ΔE-E method and E-Range method, are compared with each other. The results show that the E-Range method is better than ΔE-E method in identifying isotopes. A beam test is also performed and a 5% energy resolution is obtained for the single layer of the detector. Obvious improvement for the identification of 14 O and 15 O isotopes, which have similar energy per nucleon, is achieved by using the range information. Finally, the energy calibration methods of the detector are explored. A linear expression is used to calibrate the light output in the first crystal and an empirical equation is used to calibrate the total light output of the incident ions which stop in any crystal of the detector. The differences between the calibration and the experiment data are globally inside 5%. This PID detector can satisfy the requirements of intermediate-energy Coulomb excitation experiments.