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.     

RBS study on Na-implanted polystyrene at various doses

A study on the composition of Na-implanted polystyrene has been made by Rutherford backscattering spectroscopy (RBS). Substrates used were polystyrene (PS) dishes. Na ion implantation was performed at an energy of 50 keV with does ranging from 5᎒¹⁵ to 1᎒¹⁷ ions/cm². RBS was carried out with 1.5-MeV He⁺-ion beams and a fluence of 60 7C. The depth distribution of Na atoms showed a Gaussian distribution for the low dose. The profile is in a good agreement with a theoretical distribution calculated by a TRIM code. At the intermediate dose, the Na depth profile changed to a trapezoidal distribution. At the high dose, Na enrichment was found at the surface. Oxygen incorporation into PS is also observed. Na distribution behaviors in PS surface layer were discussed as a link to the O distribution.     

Measurement of Reaction Cross Section for 17C and Finite-Range Glauber Model Analysis

We have measured the reaction cross section σ_R of ¹⁷C on the carbon target at the intermediate energy of 97A MeV by using transmission method.finite-range Glauber model has been employed to investigate the density distribution of ¹⁷C by fitting the present result and the previous result of interaction cross section σ_I.By contrast with the result from the analysis of σ_I,a tail in the neutron density distribution of ¹⁷C is found necessary to interpret the present result.Considering the configuration of the valence neutron,a dominant 1d_5/2(77±21%)occupancy is found,which is in agreement with results of momentum distribution measurements.     

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.     

Irradiation Effect in C60 Films Induced By Low Energy Ions

Irradiation effecs, mainly including transformation from crystalline into amorphous state, of C₆₀, films induced by 120keV H, Ar and Fe ions irradiation were analysed by means of Raman scattering technique. The results indicate that amorphization process in the cases of Ar and Fe ions irradiation is dominated by nuclear collision, but in the case of H ion irradiation, the process is dominated by electronic energy transfer. The annealing effect of electronic energy loss which induced the intermediate graphitization process before amorphization in lower irradiation dose ranging from 2×10¹⁴ ions/cm² to 5×10¹⁶ ions/cm² was found in the case of H ion irradiation for the first bine.     

Isospin Effects of Threshold Energy of Radial Flow in Heavy Ion Collisions

The threshold energies of radial flow in reactions of ^40 Ca-^40Ca and ^48Ca＋ ^48Ca in central collisions are investigated within an isospin dependent quantum molecular dynamics model by using three different forms of symmetry energy. It is found that the neutron-rich system has smaller threshold energy of radial flow and this quantity depends on the form of symmetry potential. It is indicated that the threshold energy of radial flow can provide a new method to determine the symmetry energy of asymmetric nuclear matter.     

ENERGY CALIBRATION FOR A PLASTIC SCINTILLATOR BETA-DETECTOR TELESCOPE

A plastic scintillator beta-detector telecope has been buit and calibrated.The uncertainty of linear energy calibration in the range of endpoint energy between 0.7 and 6.1MeV for both β^－ and β⁺ emitters has been tested to be 35keV.     

A Simulation of Emitted Nucleons:An Extended BUU Model

On the basis of the old BUU method,the neutrons and protons of the projectile and target nucleus was distinguished,meanwhile,the droplet model which included the surface diffusion parameter,neutron skin and deformation parameter etc.was considered during simulating original nucleon's distribution.Condersing the fact σ_np≈3σ_nn≈3σ_pp in intermediate energy domain,it was incorapated into the collision term of BUU.Before studying 44MeV/A ⁸⁶Kr+¹⁹⁷Au reaction by the improved BUU model,the stability of the model has been checked,then the condition of nucleons emission was defined,finally the impact parameter dependence of the abraded neutrons and protons from the projectile was obtained,so was the correlation of TLF and PLF.     

Kinetic Energy of Trapped Ions Cooled by Buffer Gas

The average kinetic energy of 40 Ca＋ ions is measured by the method of evaporating ions in an rf ion trap. The kinetic energy of the ion 40Ca＋ varies from 0.5eV to 0.2eV with changing buffer gas pressure from 10^-7 mbar to 10^-5 mbar. The Brownian motion model is also introduced to calculate the average kinetic energy of the trapped ions.     

High Energy Unequal-nuclei Collisions and Relaxation Time in Fokker Plank Equation

In this paper,the time evolution of high energy heavy ion collisions is described by Fokker-Planck Equation.The rapidity distribution of the final state particles is analysed with this model for ¹⁶O and ³²S particles beams of 200AGeV.The relaxation time for various systems are determined.Results comparable to the usual empirical data are obtained.     

SINGLE PROTON TRANSFER REACTION INDUCED BY HEAVY ION 40Ar(11B, 10Be)41K

The angular distribution has been measured for elastic scattering on ⁴⁰Ar with ¹¹B and for the single proton transfer reaction ⁴⁰Ar(¹¹B, ¹⁰Be)⁴¹K at the incident beam energy of 50 MeV. The elastic scattering cross section has been fitted in terms of the optical model. The EFR-DWBA aproach with recoil effect has been used to analyze the differential cross section. The spectroscopic factor was extracted.     

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.     

Isotope Ratios of Light Charged Particles and Temperature in the Reactions 30MeV/u40Ar+112,124Sn

Coincidence measurements between residues and light charged particles (LCPs) have been made for the reactions 30MeV/u 40Ar+^112,124Sn. The LCPs were measured by 11 semi-conduct telescopes from very forward angle to backward angle. The times of flight of the residues were measured by PPACs installed concentrically around the beam at forward angle. The excitation energy of the primary hot nuclei was obtained from the velocity of residues in the frame of incomplete fusion model. The single isotope ratios, as function of observing angle and excitation energy have been studied. The ratio of ³He/⁴He and ⁶Li/⁷Li increases with angle while that of ⁶He/⁴He and ⁸Li/⁷Li decreases. The calculation of statistical theory can not reproduce the curve quantitatively, implying the existence of dynamic effect. Isospin effect of the primary hot nuclei on the single isotopic ratios is demonstrated. However, the temperature extracted from double isotope ratios is target independent.     

Time Scsle for Emission of Intermediate Mass Fragments in E/A=30MeV 40Ar+natAg Reaction

Fragment-fragment conelation functions have been measured in E/A=30 MeV ⁴⁰Ar+^natAg reaction via the technique of intensity interferometry. Emission times of intermediate mass fragments have been extracted from reduced velocity correlation functions by using the threebody trajectory model. The average emission time of intermediate mass fragments varies with the energy of fragments. It decreases from about 300fm/c for low energy fragments to about 80fm/c for energetic fragments. After subtmcting the contribution of projectile-like fragments, average emission times of mid-rapidity fragments are of the order of 250fm/c for this reaction.It indicates that intermediate mass fragments emitted in this reaction mainly come from sequential binary decays.     

GDR excitation by isoscalar probes: a means to determine the neutron-skin thickness

Inelastic scattering of α-particles can excite the isovector giant dipole resonance (GDR) via the Coulomb interaction. In spite of their isoscalar nature α-particles can also excite the GDR via the nuclear interaction due to the difference in the radii of the neutron and proton density distributions. The absolute cross section to excite the GDR in inelastic α-scattering is therefore a measure of this radial difference, the so-called neutron-skin thickness. Furthermore, since the GDR strength distribution has a centroid energy which depends on the nuclear radius, these studies, when performed in deformed nuclei, can measure the neutron-skin thickness along both the short and the long axes independently. Results of an experiment performed at KVI atE _α=120 MeV and small scattering angles, including 0°, to determine the neutron-skin thickness in²⁰⁸Pb,¹¹⁶Sn,¹²⁴Sn, and the deformed¹⁵⁰Nd are discussed and compared to earlier measurements and theoretical predictions. Future improvements in the experimental set-up are also discussed.     

Resonance strength measurements of the 27Al(p,γ)28Si reaction in the energy range Ep= 0.8–2.0 MeV

An excitation function of the ²⁷Al(p,%)²⁸Si reaction has been measured over the proton beam energy range E_p = 800-2000 keV using a 4? NaI segmented crystal. In the above energy range 47 narrow resonances were measured and their strengths have been deduced. The absolute efficiency of the detection system has been determined for each one of the resonances via Monte-Carlo simulation, taking into account the decay scheme of each resonance. The results of the present work are compared with literature.     

A revisit to the neutron skin thickness of neutron-rich nuclei in the statistical abrasion ablation model

The cross sections of the fragments produced in the projectile fragmentation reactions of the even calcium isotopes from A=36 to A=52 are calculated using the statistical abrasion ablation model.The neutron skin thickness are studied by investigating the fragments isotopic cross section distributions.The neutron-skin thicknesses of the calcium isotopes have a good linear correlation to the peak positions of their fragment isotopic cross section distributions.The correlation between the neutron skin thickness and the neutron density distributions of 48Ca is investigated by introducing a parameter to adjust the diffuseness parameter in the fermi-type density distribution.     

The Study of Unbound Nuclei 11N Resonance Energy Level

The excitation functions of elastic scattering proton which were measured with inverse kinematics of elastic resonance scattering reactions in GANIL and MSU have been fitted by the multi-energy level $R$-matrix theory. The final result shows that the new energy levels order for nucleus ¹¹N should be 1/2⁺,1/2^－,5/2⁺,3/2⁺, 3/2^－,5/2⁺,7/2^－,which is consistent with the experimental results of ¹¹Be (the mirror nucleus of ¹¹N) and the theoretical calculation of ¹¹N with GCM theory.     

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.     

On the Emission of Target Black Fragments in High Energy Nucleus-Nucleus Collisions

The mechanism of friction-evaporation process for target spectator contact layer in high energy nucleus-nucleus collisions is presented.The distribution of multiplicity,azimuthal and spatial angles,transverse and total momenta,as well as kinetic energy of target black fragments are calculated and compared with the experimental results of 200GeV/N ¹⁶O-Em interactions.