Hard Photon Simulation And α-clustering Nuclei Research Based On An Extended Quantum Molecular Dynamics

The study of cluster nuclei is an important subject in the field of nuclear physics.However,hadrons are strongly affected by the surrounding nuclear matter.So the struc-tural information will twist in heavy ion nuclear reactions.Compared with the tradi-tional hadronic observables,photons seldom influenced by surrounding nuclear matter,so they can carry out more untwisted information of the nuclear reaction.The purpose of this paper is to use photons as a probe to study the α clustering in nuclei.The extended quantum molecular dynamics（EQMD）model is one of the most important models used to study the nuclear reactions of α-cluster nucleus.The first work of this paper is to successfully introduce the incoherent bremsstrahlung process（pn→pnγ）into this model.However,unlike most quantum molecular dynamics（QMD）transport models,the EQMD model also takes into account dynamic wave packet degrees of freedom.Besides,the contribution of the dynamics wave packets and the zero-point center-of-mass kinetic energy to the total energy of the system,i.e.,the expected value of Hamiltonian,is also included.This design is one of the reasons why the EQMD model can successfully simulate nuclei with-clustering nuclei.But,it also increases a lot of difficulty to add the bremsstrahlung.In the original EQMD model,the traditional scattering method greatly underestimates the yield and slope of direct photons.will be greatly underestimated with the traditional treatment.Therefore,basis on the design of Hamiltonian used in the EQMD model,we suggest a self-consistent treatment which includes the contribution of dynamic wave packet to kinetic energy within the two body inelastic scattering process.Thus,it greatly improving the results of the bremsstrahlung process.In this work,we use our modified EQMD model to sim-ulate the quasi-symmetric nuclear reaction system of¹⁴N+¹²C with beam energy of/=20,30,40 Me V,respectively.This results show that both the yield of direct photons,the inverse slope of the energy spectrum and the laboratory angular distribu-tion of photons can be reasonable reproduce the experimental results well.In addition,we also simulate the asymmetric nuclear reaction system of⁴He+C and⁴He+Zn with the beam energy of/=53 Me V.The results show that the angular distribution of direct photons in the nucleon-nucleon（N-N）center of mass system,the velocity of γ-emission source and the inverse slope of the direct photon energy spectrum can be well reconstructed.Therefore,it successfully describes the bremsstrahlung process with our modified EQMD model.In the second work,we use the collective flow of photon as a probe to study the ge-ometric effects of the α-cluster nucleus in the nuclear reaction since photon is seldomly influenced by the surround nuclear matter.With the modified EQMD model,we have successfully simulated the energy spectrum of direct photon from the nuclear reaction system of⁸⁶Kr+¹²C with beam energy of/=44 Me V.On this basis,we compare the energy spectrum and laboratory angular distribution of triangular configuration with those of spherical configuration.It is found that the difference between the two different configurations will increase with the energy of the direct photons.However,it is a pity that the difference is not obvious.Then,we investigate the direct flow and elliptic flow of free photons by taking account of-clustering structure.The difference of collective flows between different configurations of¹²C is observed in this work.This indicates that collective flows of direct photons are sensitive to the initial configuration.Besides,we also compare these results with the free protons.Because the emission mechanism of free protons is different from that of photons,and they are strongly influenced by the surrounding nuclear matter.The direct flow and elliptical flow of free proton in this asymmetric reaction system are obviously distorted.When we re-extract the particles which are taking part in the bremsstrahlung process during pre-equilibrium stage,the distortion disappears.In addition,we confirm that an attractive interaction plays a dom-inant role in this reaction system at Fermi-energy range.After re-extraction,even in the case of asymmetry system,directed flow still keeps an anti-correlation relationship between direct photons and free protons.Therefore,direct photons are an alternative probe to study the mechanism of nu-clear reactions and the-clustering structure in light nucleus from heavy ion collisions at Fermi-energy region.