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.     

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.     

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.     

Radiation Protection of CSR

The construction of CSR (cooling storage ring) which includes a main ring (CSRm) and an experimental ring (CSRe) will be finished at the end of 2005. Heavy ions of carbon to uranium will be accelerated up to 900MeV/u and 400MeV/u at intensity of 10⁸ pps. The HIRFL (heavy ion research facility in Lanzhou) will be used as the injector. For the shielding design of CSR, the secondary neutrons due to the ion beam loss, their spectra and angular distributions were estimated based on the experimental results. The dose equivalent outside the shielding surface and in the surrounding environment and the neutron skyshine dose equivalent were also estimated in this study. The experimental result, neutron yield, spectrum and angular distribution for 400MeV/u ¹²C+Cu reaction were used for estimating the source term of shielding design. It is found that the most important environmental radiation impact component of CSR is the skyshine neutrons.     

Production of Hafnium Isotopes From interactions of natW With 6.3─24.6 MeV/u 40Ar Ions

The yields of known hafnium isotopes produced in 6.3-24.6MeV/u ⁴⁰Ar+^natW reactions were determined by γ-ray spectroscopy following radiochemical separations.The excitation functions,FW values and isotope distributions of hafnium were obtained.It is indicated that synthesis of new heavy neutron-rich isotopes is possible through the reactions induced by heavy ions at HIRFL energy region.The thick target is favorable for increasing the yields of neutron-rich nuclides far from the β-stability. However, further increasing incident energy is not always helpful to synthesize neutron-rich isotopes.     

INCLUSIVE NEUTRON MULTIPLICITY IN HEAVY-ION COLLISION MEASURED BY A 4π NEUTRON DETECTOR

The inclusive neutron multiplicity distribution in the heavy-ion reactions measured by a 4π neutron detector is presented in this paper.Results for ⁴⁰Ar+¹⁹⁷Au and ⁴⁰Ar+²³²Th at 27,35,44 and 77MeV/u are displayed.The distribution provides an overview on the reaction characteristics concerning the relative strength of contributions according to their degree of dissipation.     

Energetic Protons and Cold Nuclear Multifragmentation Pattern

Multifragmentation is studied in correlation with energetic protons.A cold multifragmentation pattern is proposed based on the numerical simulation of the stochastic Boltzmann-Langevin model for describing the intermediate heavy ion collisions,i.e.,a sizable fraction of the available energy is released from the system by fast non-equilibrium proton emission,in which the explosion is caused to happen by a violent,but cold expansion of the system.Some typical examples simulated for ⁴⁰Ca+⁴⁰Ca central collisions at 90MeV/u are presented.A possible experimental signature which could be detected with the help of a 4π detector system is suggested.     

A DYNAMICAL METHOD IN DEEP IN ELASTIC COLLISION OF HEAVY IONS

A method correlating the dynamical equations with the diffusion equations is developed in this paper to explain the dissipations and fluctuations of heavy ion collisions. Considering the degrees of freedom about the relative motion, rotation and asymmetric mass, the relation between the frictional and diffusion tensors is obtained.
Some imformations of deep inelastic collisions in three reaction systems are obtained by solving coupling equations numerically. The calculated results show that there are orbiting effects in the reaction systems of ⁸⁶Kr(8.18MeV/A)+¹⁶⁶Er and ⁸⁴Kr(8.5MeV/A)+¹⁶⁵Ho and there is strong focusing effect in the reaction system of ¹³⁶Xe(8.31MeV/A)+²⁰⁹Bi. But the calculated results are in agreement with the experimental data only for larger partial waves. The nuclear force and diffusion coefficients must be studied further.     

Nuclear Matter Density,Collision Number and Entropy in Dynamics Process of Intermediate High Energy Heavy Ion Collision

The nuclear matter density,collision number and entropy in the dynamic process of heavy ion collision ⁴⁰Ca+⁴⁰Ca at E_L=400MeV/A for very central collision were calculated.The results show that the nuclear spatial density distributions depend mainly on the mean field but rarely on the nucleonnucleon collisions.The density distribution in the momentum space,collision number and entropy are influenced by the mean field and nucleon-nucleon collision,especially the medium effects.     

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.     

Excitation Energy and Temperature of Compound Nuclei in the Reaction of 35MeV/u 40Ar+197Au

The fission fragments in the reaction of ⁴⁰Ar+¹⁹⁷Au have been measured coincidently with light charged particles at 35MeV/u by using large area position sensitive detectors and Si-detectors. The velocities of the fissioning compounds are deduced based on the fragments and the excitation energies of the compounds calculated with a hypothesis of massive transfer and taking into account the influence of pre-equilibrium emission of light particles. As the same time,the temperatures of the compounds are extracted by using the energy spectra of the backward light charged particles measured coincidently with fission fragments. The temperature-excitation energy curve does not present the behaviour predicted by the theories.     

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.     

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.     

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.     

Origins of the Forward Emission of Complex Fragments for 40Ar+159Tb Reaction at 30MeV/u

Light charged particles and complex fragments have been measured at forward angles in coincidence with two fission fragments for ⁴⁰Ar+¹⁵⁹Tb reaction at 25MeV/u. These three-body coincident events were sorted as a function of the impact parameter using linear momentum transfer and total transverse momenta methods. Equilibrium statistical emissions of complex fragments from quasi-target residues accompanied by non-equilibrium mid-rapidity components were found to dominate in central collisions, while projectile fragmentations were found to dominate in peripheral collision. Three components of complex-fragments from quasi-target, quasi-projectile and mid-rapidity soures were found in mid-central collision.     

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.     

The Relation of Isotopic Distribution of Heavy Ion Peripheral Reaction Products to Neutron-Skin and Excitation Energy in Intermediate Energy Range

The relation of isotopic distribution of the heavy ion peripheral reaction products in intermediate energy range to neutron-skin and excitation energy has been studied.The thickness of neutron-skin predicated by the droplet model and emperical one-body disspation in the intermediate energy range has been considered.The experimental isotopic distribution produced by ⁴⁰Ar and ⁸⁶Kr as projectiles in the intermediate energy can be reproduced by calculation.     

Target Residues from the Interaction of Indium with 42MeV/nucleon 12C Ions

The cross section is measured for 65 target residues produced from the interaction of indium with 42MeV/nucleon ¹²C ions using nuclear chemistry techniques.The experimental mass yield distribution gives a satisfactory agreement with that calculated from Monte Carlo code GEMINI based on the statistical binary decay model. According to the systematics of isotope distributions,the possibility of the production of new neutron-deficient nuclides far from β stability is discussed in the intermediate energy heavy ion reaction.     

BaF2 Used for Particle Identification in Intermediate Energy Heavy Ion Raactions

A detector telescope consisting of a BaF₂ crystal and Si detectors is used to measure forwardly emitted products in ¹²C(46.7MeV/u)induced heavy ion reactions,both ΔE-E method and fast-slow correlation method are adopted in the particle identification.The response of BaF₂ to various incident ions has been studied.     

Two Electron Transfer and Stabilization in Slow O^6＋ and Rare-Gas Collisions

The stabilization ratios R for double-electron transfer, i.e., the cross section ratios of true double capture to total double-electron transfer, are measured in O^6＋ ＋He, Ne and Ar collisions at 6 keV/u. A high R value about 68% is obtained for the He target, while for the Ar target, the R value is only 8%. The high R value for the He target is due to the significant direct population of the （2l, nl′ ） configurations with high n. For the Ar target, the （quasi）symmetric configurations （3l, nl′） lead to the much lower R value. Neglecting the core effects, the O^6＋ ion can be taken as a bare ion C^6＋ except the occupied ls shell, and then the measured R values are compared with previous experimental results of C^6＋ projectile ions at Ne and Ar target, while the occupied ls shell for the C^6＋ ＋He collisions. similar impact velocity. It yields good agreement with the O^6＋ ＋He system results in a higher R value than that in