One of the most important aspects of the products emitted in the heavy ion reaction is the complex fragments (or the Intermediate Mass Fragments−IMFs) and the Light Charged Particles (LCPs). In this paper, the emission mechanisms of the fragments and LCPs emitted in the reactions of 40Ar(25MeV/u)+115In/58Ni/27Al are investigated. Also the dynamics aspects of the fragments that come from the collision systems of 40Ar+58Ni/115In are theoretically studied over the energy range of 25−100 MeV at the Fermi energy domain.

        On the basis of the energy spectra, the angular and Z distributions, the evolution of emission mechanisms of different fragments with the variation of the detected angles in the laboratory system and the charge numbers of the fragments is discussed.The different features of the angular and charge distributions for the three targets are also presented. The energetic component of the fragments at the forward angles mainly comes from the projectile fragmentation or breakup. The projectile-like fragments in the neighborhood of the projectile have the additional contributions from quasi-elastic scattering and transfer reaction. The low energy component, which takes the small fraction of the fragment products at the forward direction, comes from DIC & fusion-like mechanism; In the intermediate angle region which is beyond the grazing angle, it is dominated by the non-equilibrium component whose velocity is about half of the beam one and the equilibrium evaporation component of the low energy.

        The Modified Quantum Molecular Dynamics (MQMD) model is employed to investigate the angular & charge number distributions of the emitted fragments.Generally, the theoretical calculations are in good agreement with the experiment data. But in the forward angles the yield of the fragments is underestimated by MQMD model while in the case of the intermediate angle region, the calculation is higher than the experiment data in some degree for the fragments whose charge number is in the vicinity of the projectile. Related analyses and discussions are presented in this paper. The angular & charge number distributions of the fragments are also compared with the statistical model of GEMINI. It is found that a small proportion of the statistical evaporation component exists in the forward angles while in the intermediate angle region, this component increases to some extent. However, its ratio is still small. With the decrease of the fragment charge number, the non-equilibrium intermediate-velocity component goes up step by step and plays a leading role while the equilibrium evaporation one diminishes gradually.

        The time evolution of the particle distribution of the reaction systems 40Ar(25 MeV/u)+58Ni/115In with different impact parameters in the X−Z plane of the configuration space is simulated with the MQMD model. The reaction mechanism dependent on the impact parameters is discussed. The relationship of the nucleon distributions between the initial and the final states is studied.

        The MQMD model is applied to study the time evolution of the collision system 40Ar+58Ni in the energy range from 25 to 100 MeV/u at Fermi energy domain. Some macroscopic physical quantities that are related to the formation dynamics of the fragments are selected to study the development of collision system from the non-equilibrium state to equilibrium one under the conditions such as different bombarded energies and impact parameters. These physical quantities include IMF mean multiplicities, the maximum and the mean densities of the reaction zone between the projectile and target, the non-equilibrium factor in the momentum space and momentum distribution width within the maximum cluster etc. The physical picture of fragment emission for the heavy ion reaction at intermediate energy region is presented in the paper. The time scale of the fragment emission is discussed. The result is that the time of 40Ar+58Ni system coming to freeze-out (state) is 65,75,90,105 and 115fm/c, respectively, when the bombarded energy are set to be 100,75,55,35 and 25 MeV/u one after another.

        It is investigated that the energy correlation between the emitted fragments of atomic numbers varying from 4 to 14 detected at θlab=15° and the LCPs including proton, deuterium, tritium and α particle at the close geometry angular configuration in the reaction of 40Ar(25MeV/u)+115In. The result shows that the existence of sequential decay mechanism. It is found that the peak position is at the small angles in the correlation angular spectra between the LCPs and the fragments, the most probable angle is at 2° or so. In the binary sequential decay, the lighter primary products (fragments) are more easier to be excited and decay to light IMFs and the LCPs, the yield of the LCPs with more heavier mass is higher than that of the lighter LCPs. The result shows that the total yield ratios summed over the fragments of Z=3−14, which are correlated with LCPs, are 1:1.3:1.78:7.57 for proton, deuterium, tritium and α particles, respectively.

        The large angle correlations for in-plane and out-of-plane have been measured for the pairs of the fragments and LCPs in the reaction of 40Ar(25MeV/u)+115In. It is obtained that the azimuthal correlation functions and the azimuthal asymmetry factors which reflect the collective rotationlike behavior or effect. The azimuthal correlation function of all pairs between fragments and α particles shows a minimum value at φ=90° plane. It indicates that the LCPs and fragments formed in the course of reaction exhibit an enhanced emission in the reaction plane due to collective rotationlike behavior effect by attractive mean field. The more heavier the mass of the coincident LCPs & fragments, the more stronger the left-right asymmetries of the coincident particles with respect to the beam direction in the reaction plane, the more preferential the particle emission to the direction opposite to the coincident reaction products. Such sorts of the same and opposite side asymmetries seem to be established duringthe initial stages of the reaction. Along with the increase of the coincident LCPs & fragments, the influences of the sequential decay and the particle final state interactions to the azimuthal correlation functions of the correlated pairs at the small relative angles in the φ=0° plane die away and vanish at last. When we exclude such influences by adding the additional integration conditions on the relative energy spectra of the LCPs & fragments, the real azimuthal correlation functions of the correlated pairs at the small relative angles in the φ=0° plane are obtained. The featureof the azimuthal anisotropic emission strongly depends on the mass of the correlated pairs, i.e., along with the increase of the mass of the correlated pairs, the azimuthal asymmetries increase and the collective rotationlike effect is enhanced. So the in-plane particle emission increases and at the same time the out-of-plane one decreases.

        The simulated test measurement of the Zero-Crossing Timing Method (ZCTM) is performed by the research pulser (ORTEC448) with the attached charge terminator instead of by the scintillator with photodiode readout (CsI(Tl)+PD). The feasibility of ZCTM is verified successfully. And it is the first time the Laplace Transform Method (LTM) based on the electronics signal-process theory is introduced to analyze the electronics network circuit of the ZCTM for identifying the LCPs. The calculation reproduces the test result of the simulated measurement very well. Furthermore, the theoretical results successfully explain influences of the selection of the spectroscopy amplifier parameters on the identification of LCPs with the CsI(Tl) scintillators. The optimum shaping time constant τopt(about 6μs in our case) for the system configuration is deduced. The above method and result are helpful in the design of the electronics circuit module matched specially with these kinds of CsI(Tl)+PD detectors. It is also discussed that the significance of application of LTM in the signal-process theory at the heavy ion experiments.

        In order to explore the nature of the fragments and LCPs emitted in the 40Ar(25 MeV/u) induced reaction, we have developed two sets of logarithmic multi-stage detection systems with the large dynamic range and other detectors used in heavy ion reaction at the intermediate energy domain. The logarithmic multi-stage detection system can give the energy and position signal simultaneously. The most important characteristics of such logarithmic multi-stage detection system are good energy and position resolutions, high Z identification power, low energy threshold and large dynamic ranges for particles and energies. It is one ideal fragment detection system for the performances of the heavy ion experiments.