The Angular Distributions of intermediate Mass Fragments Emittsd in 30 MeV/u 40Ar+58,64Ni and 115In Reactions

The angular distributions of intermediate mass fragments with Z=3-19 emitted in 30 MeV/u ⁴⁰Ar+^58,64Ni and ¹¹⁵In reactions over an angular range of 5°—140°have been measured.Exponential distribution function: dσ/dΩ=N·exp(-θ/a) was used tO fit the measured angular distributions.We have extracted the decay factor a that can be connected with the interaction time τ, and the factor N that is related to the intensity of the emission source.The relationships of a(Z) with Z and N(Z) with Z for different reaction systems and different angular ranges have been discussed. The dependence of angular distributions on isospin and the symmetry of reaction system have also been discussed.     

Measurement of Angular Cross Correlation of the Cross Section Fluctuation in Dissipative Collision 27Al+27Al

The excitation function was measured from θ_lab=10.4° to 57.4° in dissipative collision ²⁷Al+²⁷Al with incident energy ranging from 114 to 123 MeV in step of 200 keV. The Angular-cross Correlation Functions (ACFs) of cross section fluctuation within large angle region were obtained through experiment for the first time. It is found that the angular coherent width is at least 40°. It is interesting that the ACFs is not simple bell shape but shows strong asymmetry. The over-all behavior is that ACF varies more quickly for the backward angles. Itis also noticed that the cross section fluctuation in the forward angle region (θ_cm<70°) shows much stronger angular coherence than in the backward angle region (θ_cm>70°). This angular dependence may be attributed to the coherent rotation effect of intermediate dinuclear system.     

Relaxation of Isospin Degree of Freedom in the Reactions 36Ar+112,124Sn at 35MeV/u

Isotope ratios,defined as the yield ratio of two isotopes with the same charge,were analyzed as a function of kinetic energy of outgoing particles at 20° in the reactions of ⁴⁰Ar+^112,124Sn and 5°in³⁶Ar+^112,124Sn at incident energy of 35MeV/u. Isotope ratios between the neutron-deficient isotopes and stable isotope increase with kinetic energy,while those between the neutron rich isotopes and stable isotope decrease. This different behavior was observed similar for both ¹¹²Sn and ¹²⁴Sn targets. The isotope ratios show rather obvious target dependence at 20° and little target dependence at 5°. As the outgoing energy getting down,the N/Z ratio of the fragmentation products at 5° diverts gradually from the N/Z ratio of the projectile to that of the system. These observations indicate that the isospin degree of freedom does not reach complete equilibrium in the peripheral or semi-peripheral collision at this bombarding energy.     

Measurement of Excitation Function and Analysis of StatisticalProperty in 27Al+27Al mssipative Reaction

The angular distribuhon in the range of 0_cm=50°—90° and excitation funchon of the reachon products in heavy ion dissipahve reachon ²⁷Al+²⁷Al were measured, in the incident energy region from 114MeV to 120MeV with 200keV step. The statishcal property of the fluctuation of the excitation funchon in heavy ion dissipative reaction was discussed based on the integration of the macro outgoing channels.     

The Angular Dependence of the Coherence Energy in Dissipative Reaction of 19F+51V

Excitation function fluctuations for projectile-like fragments from ¹⁹F+⁵¹V dissipative reaction within the energy region of 102.25—109.50MeV are reported.The statistical method is applied to the analysis of energy coherence in the cross rection fluctuations and the strong cross correlation between exit channels is obtained.The dependences on charge number and on mass number are presented.The relation between angular velocity damping and the rotational energy dissipation is discussed.     

Origins of Intermediate Mass Fragments for 40Ar+natAg Reaction at 30 MeV/u

The energy spectra of intermediate-mass fragments (IMF) (3≤Z≤16) have been measured from 6° to 110° for ⁴⁰Ar+^natAg reachon at 30 MeV/u. The energy spectra were analyzed by the moving source model. The natUres of the projechle-like source, target-like source and mid-rapidity source as well as the evolution with angle and nuclear charge were discussed. Two intermediate mass fragments, measured by correlation method in forward angles, come from two sources. One comes from projectile-like source, and other one mainly comes from intermediate source respectively.     

Investigation of Intermediate Mass Fragments Emitted in the Reaction of 294MeV 20Ne+159Tb

Intermediate mass fragments(2Z≤11) emitted from 294 MeV ²⁰Ne+¹⁵⁹Tb reaction have been measured by △E-E telescope counters at the angle of 10°—150°region.The energy spectra of the fragments at back angle(>90°) have bell shape,and their peaks locate near the Coulomb barrier of exit channel.The analysis of the energy spectra has been done in terms of moving source and indicate that all the fragments are emitted from a common source,the compound nuclei formed in incomplete fusion process.The charge and angular distributions of the fragments originated from the asymmetric binary decay of the formed compound nuclei have been calculated based on statistical GEMINI code,and the results are in well agreement with the experimental data.     

Angular and Z Distributions of the Fragments at Forward and Intermediate Angles in the Reaction of 25MeV/u 40Ar+115In,58Ni,27Al

The angular & Z distributions of foe fragments emitted in the forward and intermediary angles are measured at the reaction of 25 MeV/u ⁴⁰Ar+¹¹⁵In,⁵⁸Ni,²⁷Al. Their characteristics are investigated based on the model of Modified Qantum Molecular Dynamics (MQMD). 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 numbers are in the vicinity of the proiectile. The angular & charge distributions of the fragments are also compared with the statistical model of GEMINI. The results turn out to be 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. It is found that the equilibrium evaporation component decreases gradually when the Z of the fragments becomes smaller.     

THE MASSIVE TRANSFER IN 12C+197Au REACTION

In this paper, we present energy spectra and angular distributions for the α-par-ticles emitted in the reaction of ¹²C+¹⁹⁷Au at 64 and 67 MeV and for α, Be and B emittedin the reaction at 71.5 MeV. The most-probable energles of the variousproducts emittedin this reaction decrease.with decreasing incident energy. The angular distributions peak near grazing angle.The peak position of the angular distributions shift from--80°to--120°while the projec-tile energy decreases from 71.5 MeV to 64 MeV. These all show the features of the transferreaction. The ⁶Li product also has been measured and the ⁸Be particle emitted from thisreaction was detected at 90°to the beam direction using α-α coincident technique at 71.5MeV. The coross section of the ³Be is only few percent at the same angle.     

Evaporation of Intermediate-Mass Fragments From Hot-Nuclei in Reaction 40Ar+159Tb at 25MeV/u

The inclusive energy spectra of intermediate-mass fragments(IMF)(3≤Z≤9)have been measured in the range from 20°to 155°for ⁴⁰Ar+¹⁵⁹Tb reaction at 25MeV/u.At backward angles,the spectra of IMF show a characteristic of statistic evaporation and can be well fitted by a moving source with same parameters.The obtained source velocity and temperature are in agreement with the corresponding values of hot nuclei produced in an incomplete-fusion process.Therefore,it seems that there IMF are statistically evaporated from a same source.The experimental results have for compared with the predictions of the statistical model using GEMINI code.     

Optical Potential Parameters of Weakly Bound Nuclear System 17F+13C

Elastic scattering angular distributions of the 14^N＋16^O system and the angular distributions of transfer reaction 16^O（14^N,13^C）17^F at ELab=76.2 MeV and 57 MeV have been measured and calculated by means of the exact finiterange distorted-wave Born approximation with the PTOLEMY code. The optical potential parameters for the weakly bound nuclear system 17^F＋13^C have been deduced and applied to analyse the elastic scattering angular distributions of the similar systems 17^F＋12^C and 17^F＋14^N which are taken from literature. The result shows that the transfer reaction with stable projectile and target combination can be used as an alternative method to extract the optical potential parameters for the weakly bound nuclear system.     

Linear Momentum Transfer in the Reactions Induced by 50MeV/A12C Bombarding 209Bi and 197Au

The Distributions of the linear momentum transfer (LMT) in the reactions induced by 50MeV/u ¹²C with ²⁰⁹Bi and ¹⁹⁷Au were measured using fission fragment angular correlation technique.The most probable value of the linear momentum transfer per projectile,p^mp is dependent on the target.173MeV/c and 184MeV/c for ²⁰⁹Bi and ¹⁹⁷Au were obtained.In these distributions,there exists a small hump around 0.3 of LMT,which can probably be attributed to the alpha cluster transfer.     

Origins of the Neutrons Emission in the Reaction of 33.4MeV/u 17N on 9Be

In the reaction of 33.4MeV/u ¹⁷N on a target ⁹Be,the measured neutron spectra at different angles exhibit a complex pattern and vary regularly as a function of the detected angle. The detected neutrons probably come from the three origins:nucleon-nucleon collisions between the projectile and target,break-up of ¹⁷N and statistical evaporations from the hot nuclei. By analyzing the measured neutron angular distribution and calculating with QMD and GEMINI for the reaction concerned, 4.49,0.44 and 5.5barns were obtained for neutron emission cross sections due to the three origins mentioned above,respectively.     

Production of Helium Projectile Fragments in 16O-Emulsion Collisions at 60 A GeV

Production of helium projectile fragments in ¹⁶O-emulsion interactions at 60 A GeV is investigated. The total charge changing and partial production cross-sections are measured experimentally on the basis of helium multiplicity. The multiplicity distribution of helium projectile fragments obeys a KNO scaling. In the peripheral collision of ¹⁶O at 60 A GeV in nuclear emulsion, the production of target fragments depends on the multiplicity of helium projectile fragments linearly. The averge multiplicity of target fragments decreases with the increasing of the number of helium projectile fragments which can be well expliained by the model of participant-spectator (the nuclear geometric model) of nucleus-nucleus interactions.     

RESEARCH OF RELAXATION PROCESS INDUCED BY 80.6MeV 16O ON 27Al

The decreasing coefficients of the angular distributions, the charge distributions and the first and second moments of the charge distributions with variation of TKEL are deduced from the results of the measurement of projectile-like fragments produced by 80.6MeV ¹⁶O on ²⁷Al. The relaxation process of this reaction is analysed, the effects of the potential energy surface on the first and recond moments of charge distributions are discussed.     

Energy Correlations between Fragments and Light Charged Particles in Reaction of 25MeV/u 40Ar+115In

The correlations between the emitted fragments at θ_lab=15°and the light charged particles(LCPs) at the close geometry configuration in the reaction of 25MeV/u ⁴⁰Ar+¹¹⁵In were measured. The energy correlations between fragments (4≤Zf≤14) and the LCPs including proton, deuterium, tritium and a particle as well as the energy spectra of the LCPs were obtained. The result shows the existence of sequential decay mechanism. It is found that the peak position of angular correlation is at the small angles and the most probable correlation angle is at 2°or so; The peak positions of the two components in the energy spectra of LCPs increase gradually with the mass of correlated partner; The lighter primaly products are more easier to be excited and decay to IMFs and the LCPs. In the Sequential decay, the yield of the LCPs with more heavier mass is higher than that of the lighter LCPs. The result reveals that the total correlation yield ratios summed over the fragments of Z_f=4—14 are 1: 1. 3: 1. 78: 7. 57 for proton, deuterium, tritium and a particles, respectively.     

Analysis of the Energy Autocorrelation Functions in Dissipative Heavy Ion Collision of 27Al+27Al

The excitation functions of the dissipative fragments emitted from the reaction of ²⁷Al+²⁷Al have been measured in the energy region from 114MeV to 127MeV in steps of 200keV. The detection system covered continuous angles from 10° to 57° in laboratory system. The energy autocorrelation functions of the dissipative fragments have been analyzed by using different approaches,especially using the statistical nuclear reaction model with memory. The results indicate that the intermediate dinuclear system formed in the dissipative process is set in a damped coherent nuclear rotation which causes the nonself averaging oscillation structure in the excitation functions and originates from a typical quantum chaotic motion.     

Complete and Incomplete Fusion in the Reaction of 65Cu With 16O Ions

The excitation functions,angular distributions and differential range distributions have been measured for target residues from the reaction of ⁶⁵Cu induced by 45—96MeV ¹⁶O ions with radiochemical techniques.A comparison of the experimental data with Monte-Carlo simulations based on the statistcal model of compound nucleus that the heavy residues are produced by the decay of a compound nucleus formed by complete fusion.Incomplete fusion or massive transfer are the main reaction mechnisms leading to production of the residues with mass number close to that of the target.     

THE MEASUREMENT OF COMPLETE FUSION CROSS-SECTIONS FOR THE REACTIONS 12C+27Al, 12C+209Bi AND 14N+Pb

Mica track detectors were used for the measurement of evaporation residues and fission fragments of compound nuclei formed in ¹²C+²⁷Al, ¹²C+²⁰⁹Bi and ¹⁴N+Pb reactions. The complete fusion cross-sections and excitation functions were then obtained. By using the sharp cut-off model approximation, the values of the critical angular momenta were extracted from the complete fusion cross-sections. The results obtained were compared with the calculations based on current theories for critical angular momentum; they were found to agree within experimental uncertainties.     

Optical Potential Parameters for Halo Nucleus System ^6He＋^12C from Transfer Reaction ^11B（^7Li, ^6He）^12C

The optical potential parameters for the halo nucleus system ^6He＋^12C are extracted from fits to the measured angular distributions of ^11B（^7Li, ^6He）12C reaction at energies of 18.3 and 28.3MeV with distorted-wave Born approximation analysis. The characters of the obtained optical potentiM parameters are basically consistent with the results extracted from the fits to the elastic-scattering angular distributions in the literature.