Effect of Rotational Degree of Freedom on the Enhanced Prescission Particle Emission in 10.6MeV/u 84Kr+27Al Reaction

Effect of the rotational degree of freedom of In nucleus in three dimension space on prescission particle emission in 10.6MeV/u and 8.5MeV/u ⁸⁴Kr+²⁷Al collisions was studied in the framework of a statistical model. The calculation results show that for the latter incident energy,particle emission is insensitive to the rotational degree of freedom,while for the former one,the incorporation of this factor leads to the reduction of the extracted fission delay time from 20×10^－21s to 7.5×10^－21s,indicating the existence of this effect. The result also demonstrates that this effect is unable to completely account for the experimental data. In addition,the effect of rotational degree of freedom on particle evaporation prior to scission was found to depend on the excitation energy.     

Temperatures and Excitation Energies of Hot Nuclei in Reactions of 40Ar+natAg,209Bi at MeV/u

Coincidence measurements of fission fragment and light charged particle have been perfotrmed for the reactions of ⁴⁰Ar+^natAg,²⁰⁹Bi at E/A=25MeV using 4 PPAC and 11 sets of ΔE-E telescopes.Angular correlations of fission fragment were ploted as a function of the folding angle between the two detected fission fragments.The linear momentum transfer distributions were derived by measuring angular correlations.The backward spectra of light particles detected in coincidence with fission fragments having different average〈LMT〉are analyzed with Maxwell distribution.After some corrections the initial temperatures of the hot nuclei are determined from the energy spectra.The excitation energies corresponding to the different average〈LMT〉are obtained considering the reaction Q values and pre-equilibrum emission.In the central collision of the ⁴⁰Ar+^natAg,²⁰⁹Bi reactions,excitation energies are measured to be about 4.2MeV/u,2.4MeV/u and temperatures about 6.1MeV,5.5MeV,respecdvely.In semi-central collision,excitaionen energies are measured to be about 3.5MeV/u,1.9MeV/u and temperatures about 5.8MeV,4.8MeV respectively.     

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.     

New Neutron-Rich Isotope 208Hg

The new neutron-rich isotope ²⁰⁸Hg has been identified for the first time from the reaction products in fully-stopping thick ^nat.Pb target bombarded by 30MeV/u ¹²C beam provided by the Heavy Ion Research Facility in Lanzhou.Assignment of the nuclide ²⁰⁸Hg was based on the measurements of the deacy γ energy and halflife of its daughter ²⁰⁸Ti,which was grown up with ²⁰⁸Hg β-deacy.The half-life of ²⁰⁸Hg β-deacy was determined to be 42+23－12 min.The average production cross section of ²⁰⁸Hg over the incident energy region from Coulomb barrier to 30MeV/u is found to be 1.1±0.5μb.     

Radial Expansion Flow in Reactions of 40Ca+58Fe and 40Ca+58Ni

By means of using an isospin-dependent Boltzmann-Langevin equation which includes isospin-dependent symmetry energy, Coulomb energy, isospin-dependent nucleon-nucleon cross sections, Pauli blocking, and initialization, the radial expansion flow of reaction systems ⁴⁰Ca+⁵⁸Ni and ⁴⁰Ca+⁵⁸Fe at 53, 100, 150, and 200 MeV/u in the central collisions were studied. It has shown that the more neutron rich system exhibits smaller radial expansion flow. It was found that the neutron rich system had smaller threshold energy which may provide a new method to determine the isospin dependent nuclear equation of state from calculated result and linear fitting result.     

Angular Distribution of the 12C(6He, 7Li)11B Reaction

Angular distribution of the ¹²C(⁶He,⁷Li)¹¹B transfer reaction is measured with a secondary ⁶He beam of 36.4MeV for the first time. The experimental angular distribution is well reproduced by the distorted-wave Born approximation (DWBA) calculation. The success of the present experiment shows that it is feasible to measure one-nucleon transfer reaction on a light nucleus target with the secondary beam facility of the HI-13 tandem accelerator at China Institute of Atomic Energy (CIAE), Beijing.     

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.     

Isospin Effect on Relative State Population Temperature in the Reactions 40Ar+ 112,124Sn at 30MeV/u

An array of 13 detector telescopes has been used for detecting small-angle particle-particle correlations in the reactions ⁴⁰Ar+^112,124Sn at 30MeV/u. The α-α correlation functions were extracted from two-particle coincident events. A three-body trajectory code MENEKA was used to calculate the background correlation function. The detection efficiency was calculated by using the Monte-Carlo method. After subtracting the background correlation and making the detection efficiency correction, the temperatures of 4.18±0.25 0.21 MeV and 4.10±0.22 0.20MeV are obtained from relative populations of ⁸Be states for the reaction systems with different isospin,⁴⁰Ar+¹¹²Sn and ⁴⁰Ar+¹²⁴Sn, respectively. From the relationship between the state population temperature and outgoing particle energies, it is found that the emission temperature decreases with increase of the particle energies for both studied reaction systems. For the neutron deficient system ⁴⁰Ar+¹¹²Sn the emission temperature is 5.13±0.30 0.26MeV for the lower emitting particle energies and 3.87±0.37 0.29MeV for the higher emitting particle energies. And for the neutron rich system ⁴⁰Ar+¹²⁴Sn the emission temperature is 5.39±0.30 0.26MeV for the lower emitting particle energies and 3.32± 0.28 0.23MeV for the higher emitting particle energies. This kind of isospin dependence is discussed.     

Isospin Effect on the Emission Mechanism of Hot Nuclei in 35MeV/u 40Ar +112Sn/124Sn Reactions

As an extension of radioactive ion beam physics, the research on isospin dependent properties of hot nuclei has increasingly attracted considerable interest. The isospin effect on the decay of hot nuclei in reactions 35MeV/u ⁴⁰Ar+¹¹²Sn/¹²⁴Sn has been investigared. It is concluded that due to Coulomb repulsion and instability, proton-rich hot nuclei probably emit prides such as a with high energy to increase their neutron-proton ratio. Moreover, the decay chain for those particles is seemingly long and the emission Probability is high. Thus, the conventional observations, for instance, the ‘slope temperature’ extracted from energy spectrum, may very appreciably with the measured particles.     

About Three-Body Exit Channel in the Reaction 12C+16O at EL(16O)=56MeV

Three-body exit channel in the reaction ¹²C+¹⁶O at 56MeV has been studied by using measurement of the coincidence between the two changed particles.The projected spectra of the coinsidence between the two α-particles shows that the channel α+²⁴Mg is the main intermediate process of three-body exit channel α₁+α₂+²⁰Ne in the reaction ¹²C+¹⁶O at 56MeV.The analysis of theoretical calculation showed that the sum of sequential decay and statistical break-up fit the experimental spectra satisfactorily.     

Emission Time Measurements of Light Particles from 40Ar+197Au Collisions in Intermediate Energies

Particle-particle correlation functions have been measured for ⁴⁰Ar+¹⁹⁷Au collisions at E=25 MeV/u.Emission time of light particles has been extracted from correlation functions using the three-body trajectory model.The average emission time varies with the energy of particles. It decreases from about 300 fm/c for low energy particles to about 100fm/c for energetic particles.     

Light Particle and Complex Fragments Emission from 12C Induced Reactions on 58Ni,64Ni at E/A=46.2MeV

Energy spectra of light charged particles and complex fragments emitted in the interaction of 46.2MeV/u ¹²C with different target ⁵⁸Ni,⁶⁴Ni,¹²C,¹⁹⁷Au and ²⁰⁹Bi have been measured by telescopes,consisting of CsI(Tl) and surface barrier detector stacks.These telescopes for light charged particles and complex fragments have good energy resolution and mass identification.The inclusive data have been analysed within a moving source parametrization.The complex fragment yields from different targets have been compared at several angles.The systematic variation of deduced isotope yields ratios with different reaction systems is used to detemine the N/Z degree of freedom equilibration of the system achieved.     

Research on High Spin States in 68Ge,65Ga and 67Ga

The high spin states in ⁶⁸Ge,⁶⁵Ga and ⁶⁷Ga were studied through in-beam gamma-ray spectroscopy experiment.The reaction ⁴⁶Ti(²⁵Mg,xpxn) was used with beam energy 68MeV.In ⁶⁸Ge the new multiplicity of band structures,the crossing transitions among the bands and a new band with possible big diformation were observed.The experiment results agree with a new microscopic model calculation (EXCITED FED VAMPIR).In ⁶⁵Ga and ⁶⁷Ga a few band structures with strong collectivity were observed and the new level schemes were given.     

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.     

Entrance Channel Dependence of the Correlation Function of IMFs in 36Ar+112,124Sn at 35MeV/u

The reduced velocity correlation functions of the Intermediate Mass Fragments (IMFs) were measured in the reactions of ³⁶Ar+^112,124Sn at 35MeV/u. The anti-correlation at small reduced velocities is more pronounced in ³⁶Ar+¹²⁴Sn system than that in ³⁶Ar+¹¹²Sn system. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three-body Coulomb repulsive trajectory code (MENEKA) is employed to calculate the emission time scale of IMFs for the both systems. The time scale is 150fm/c in the ³⁶Ar+¹¹²Sn system and 120fm/c in the ³⁶Ar+¹²⁴Sn system, respectively. A calculation based on an Isospin dependence Quantum Molecular Dynamics code (IQMD) reveals that the emission time spectrum of IMFs is shifted slightly leftwards in ³⁶Ar+¹²⁴Sn compared with that in the ³⁶Ar+¹¹²Sn system, indicating a shorter emission time scale. Correspondingly, the central density of the hot nuclei decreases faster in ³⁶Ar+¹²⁴Sn than in ³⁶Ar+¹¹²Sn.     

Azimuthal Distribution and Azimuthal Correlation of the Particles in 10.6MeV/u 84Kr+27Al Collision

The light charged particle emission in coincidence with fragmemts in 10.6MeV/u ⁸⁴Kr+²⁷Al collision is studied.Emphasis is laid on the characters of two-order anisotropy coefficient of Fourier expansion up to two order from fitting particle azimuthal distribution and particle-particle azimuthal correlation.The derived results prove that particle emission is statistically independent with the same azimuthal distribution in each event.It is found that two-order anisotropic coefficient depends weakly on the fragment mass and increases with increasing emitted particle mass.     

Element Distributions of Intermediate Mass Fragments Emitted in 30 MeV/u 40Ar+58,64Ni and 115In Reactions

The element distribuhons of intermediate mass fragments (IMF) emitted over an angular region of 5°—140° have been measured in the reachons of 30MeV/u ⁴⁰Ar+^58,64Ni and ¹¹⁵In. Within 20°—80° range the IMFs with Z=3-24 were observed. The IMF production cross section changes smoothly with its charge number,and the element distribuhon changes continuously when the IMF charge number increases across the charge number of the projectile. There is no strong dependence of the element distribution on the charge number of the projectile in this angular region.The transition nature of the reaction mechanism in the intermediate energy region and the power law of the IMF element distribution,as well as the dependence of element distributions on the threshold of the detectors were discussed.     

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.     

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.     

Target Residues from the Interaction of Copper with 40MeV/u 40Ar Ions

Cross Sections and average forward recoil range FW were measured for target residues from the interaction of Cu with 40MeV/u ⁴⁰Ar ions using off-line y-ray spectroscopy.The mass yield distribution was obtained with assumption of charge distribution.The linear momentum transfer was calculated from FW values.A comparison with similar results of ¹²C+Cu and ²⁰Ne+Cu reactions indicates that the fractional linear momentum transfer,corresponding to central collisions,decreases with increasing projectile mass at the same energy per nucleon. However,the excitation energy of the composite system created from the collisions of Cu with ⁴⁰Ar ions reached the value of 5.3MeV /u and was higher than those from the collisions with ¹²C and ²⁰Ne ions.