Experimental Studies On Emission Time Scale Of Isospin Dependent Light Particles

Isospin dependent nuclear equation of state(symmetry energy)is an important issue for nuclear and astronomy physics,especially when the density of nuclear matter is far from the normal.The density dependence of symmetry energy influences not only the thickness of neutron skin in nuclear structure,the structural properties of neutron stars and the gravitational waves from neutron star merging in nuclear astrophysics,but also isospin transformation and the emission time scale of light charge particles in heavy ion collisions.The value of symmetry energy near the saturation density of nuclear matter is relatively certain,but there is still great uncertainty in the trend of its variation with density.Therefore,it is an important topic to find isospin related physical probes and explore the properties of symmetry energy density dependence in experiments.The small angle correlation function method is the application of HBT(Hanbury brown and Twiss)method in nuclear physics.It is a method to obtain the space-time properties of the heavy ion collision region by measuring the momentum of two coincidence particles in a small relative angle.HBT method requires high angle resolution of detector,and the development of silicon strip detector provides an opportunity for us to measure the particle correlation function accurately.Heavy ion collision is the most important method in laboratory to understand isospin dependent equation of state of nuclear matter while the emission time scale of isospin dependent particles carries the information of the isospin properties.For this purpose,a CSHINE(compact spectrometer for heavy ion experiment)heavy ion nuclear reaction detection system was built,which was consisted of parallel plate avalanche gas detectors for fission fragments measurement and silicon strip detector-CsI(Tl)particle telescopes for light particles measurement.In 2018,the 30MeV/u40Ar+197Au beam experiment was completed at RIBLL1 terminal of Lanzhou Institute of modern physics.In the data analyzing,a complete calibration and particle identification framework is established.The hit pattern recognition algorithm of silicon strip telescope is completed,and the HBT correlation function results of different particles are reconstructed.The performance of the detection system and effectiveness of data analyzing can be confirmed by the decay of the resonant states structure on the spectrum of ?-? correlation function.The N/Z values(neutron-proton ratio)of light particles is significantly different.Therefore,the isotopic products of hydrogen and helium are mainly measured in the experiment.By comparing the results of the same kind of particle pairs correlation functions between experiment data with the theoretical calculation,a reasonable proton emission time scale is obtained ?p?100fm/c.The velocity-gated correlation functions of p-d,p-t and d-t pairs show the emission sequence of ?p>?d>?t,which indicates that the neutron-rich particles are emitted relatively faster.In addition,the preliminary ImQMD calculation shows that the emission time scale of isospin dependent particles may be an effective method to study the symmetry energy in heavy ion collisions.At the same time,the positive correlation peak caused by the quantum effect was observed on the correlation function of d-d and t-t,which was rarely discussed in previous experiments.It may be of great significance for us to deeply understand the interaction between nuclei.