Cross sections and dynamical properties of a emitters produced in interactions of 12C at 86 MeV/n on medium and heavy targets

Cross sections, mean recoil ranges and angular distributions of radioactive a emitters produced in ¹²C, induced reactions at 1 GeV on medium and heavy targets are presented. A new on-line electrostatic collection device is used. A wide spectrum of heavy residues corresponding to various mass losses away from the target between D to 60 a.m.u. has been observed. A phenomenological analysis based on the statistical decay of possible precursors gives some information on the properties of the primary interaction. Losses of 10 to 30 nucleons can be partly fitted by the intranuclear cascade model. For greater mass losses, more collective primary interaction is needed. The abrasion-ablation model can produce such residues but in its clean cuts approximation the predicted excitation energy is too low.     

Implications of the target residue mass and charge distributions in the interaction of 8.0 GeV20Ne with181Ta

Target residue mass and charge distributions have been measured radioanalytically for the reaction of 8.0 GeV²⁰Ne ions with Ta. These distributions are very similar to those distributions observed in the reaction of Ta with protons of equivalent total energy rather than equivalent velocity. Detailed comparisons of the production cross sections for near target residues with abrasion-ablation model calculations show these products to have an excitation energy of ～75 MeV.     

Residual nuclei after antiproton annihilation in Mo and Ho

The distributions of residual nuclei after annihilation of stopped antiprotons in⁹²Mo,⁹⁵Mo,⁹⁸Mo and¹⁶⁵Ho targets have been measured by means of the induced radioactivity. In the case of the¹⁶⁵Ho target the residual nucleus¹¹⁶Te was observed thus indicating that about 50 nucleons may be emitted after annihilation. The distributions have also been calculated with two versions of an intranuclear cascade model. The agreement between theory and experiment is satisfactory. The effects of heavy mesons in the annihilation process, of local reduction of the nuclear density during the intranuclear cascade and of multifragmentation are discussed.     

Nuclear reactions of medium and heavy target nuclei with high-energy projectiles

Nuclear reactions induced by 3·65 A GeV¹²C-ions and 3·65 GeV protons on target elements⁵⁵Mn,⁵⁹Co,^nat Ni and^natCu were investigated by using the foil stack activation technique and Ge(Li) gamma-ray spectroscopy. Charge dispersions and mass-yield distributions of radioactive residues were obtained from the parametrization of measured spallation cross sections. Discussion of results from this and other radiochemical reactions of high-energy protons and¹²C-ions with complex nuclei is presented in terms of the concepts of limiting fragmentation and factorization.     

Angular distribution measurement for ~(12)C fragmentation via ~(12)C + ~(12)C scattering at 100 MeV/u

The angular distributions and energy spectra of~(11)B,~(10)B,and~9Be fragments of~(12)C in the angular range from 1.0°~to 7.5°~at 100 Me V/u were obtained via~(12)C+~(12)C scattering.Detailed comparisons are presented between the experimental data and the modified antisymmetrized molecular dynamics(AMD-FM),binary intranuclear cascade model(BIC)and Liege intranuclear cascade model(INCL++).The experimental angular distributions and energy spectra are well reproduced by the AMD-FM calculations but fail to be reproduced by the physical models installed in the Geant4 program,including the BIC and INCL++models.     

Study of fast target protons in high energy hadron-nucleus collisions

Intranuclear cascade model calculations are carried out on the recent measurements (WA80 Collaborations) for the multiplicity, energy and angular distributions of singly charged target fragments of energy in the range 30 E < 400=" mev=" (the=" so-called=" grey=" particles)=" produced=" in=" proton-nucleus=" interactions=" at=" 200=" gev/c.=" it=" is=" shown=" that=" these=" distributions=" are=" reasonably=" well=" understood=" in=" terms=" of=" the=" intranuclear=" cascade=" model=" which=" considers=" that=" grey=" particles=" are=" only=" produced=" in=" the=" first=" two=" generations=" of=" the=" cascade.=" the=" obtained=" distributions,=" mean=" values=" and=" target=" mass=" dependence=" are=" more=" consistent=" with=" the=" experimental=" data=" than=" other=" models=" using=" monte=" carlo=">     

Isospin dependence of the isotopic distributions from 36Ar and 40Ar fragmentation at about 60 MeV/nucleon

Fragments produced in the reactions of 69 MeV/nucleon ³⁶Ar and 55 MeV/nucleon ⁴⁰Ar on a Be target have been measured experimentally. The isotopic distributions from fragmentation reaction for both projectiles are compared with modified statistical abrasion-ablation model calculations. A strong isospin effect exhibits in the fragment distributions produced in ³⁶Ar and ⁴⁰Ar fragmentation. Experimental evidence for the disappearance of the isospin effect in the isotopic distributions produced by projectile fragmentation is observed with the increase of the violence of nuclear reaction. Received: 15 November 2000 / Accepted: 11 April 2001     

Isotopic distributions of fragments in intermediate energy heavy ion reactions

We use measured isotopic yields of fragments produced in the reaction ⁴⁰Ar on ⁶⁸Zn at 27.6 MeV/nucleon in order to see whether these quantities may constitute a test which allows to gain some insight into the projectile fragmentation process. We compare the experimental distributions to those obtained with the multisequential decay model which we developed previously, the projectile break-up model proposed by Friedman and abrasion-ablation model calculations.     

Target mass dependence and intranuclear cascade in high energy nucleus-nucleus collisions

Intranuclear cascade, one of the most important non-linear effects in high energy nucleus-nucleus collisions, is investigated, its influence on the target mass dependence of the distributions of final state particles is discussed. Using hydrodynamical model to treat non-linear effects, the main features of the rapidity distributions and their dependence on the target mass are naturally explained. The results of numerical calculation for¹⁶O-A central collisions at 60 and 200A GeV agree with the existing data.     

Multifragmentation in the intranuclear cascade — percolation approach

Results of intranuclear cascade calculations followed by a percolation procedure lead to an encouraging comparison with the experimental mass distributions observed in proton and heavy ion induced reactions in the intermediate energy domain. The predictive power of the model as well as its implications and limitations are examined.     

Comparison of α-particle and3He multiplicities from proton and π− induced reactions

Multiplicity distributions of α-particles and³He's emitted in π^? absorption and 62 MeV proton induced reactions are compared in shape and absolute value. The conclusion is reached that both primary nucleons from π^? absorption are active in initiating an intranuclear cascade, in a single absorption event, which may lead to emission of fast helions.     

Nuclear reactions of medium and heavy target nuclei with high-energy projectiles III. Emission of24Na and28Mg fragments

The emission of²⁴Na and²⁸Mg fragments in the reaction induced by 3·65 A GeV¹²C-ions and 3·65 GeV protons on Mn, Co, Cu, Ag, Au, and Pb targets has been studied. The experimental ratios of forward-to-backward emission and the mean ranges of these fragments were used to obtain the corresponding kinematic parameters. The results are analyzed by means of the two-step vector velocity model.     

Fragmentation of stable and neutron-rich 12-16C into boron fragments at approximately 240 MeV/nucleon

The elemental fragmentation cross sections of boron fragments produced by stable and neutron-rich^12-16C beams with a carbon target were systematically measured at an incident beam energy of approximately 240 MeV/nucleon.The measured cross sections were found to increase as the projectile mass number increases.The observed feature is explained qualitatively based on the abrasion-ablation two-stage reaction model and is compared quantitatively with predictions from various reaction models,including empirical and statistical models.All models agree with the measured cross sections within a factor of 2.     

Thermal multifragmentation of hot nuclei and liquid-fog phase transition

Multiple emission of intermediate-mass fragments (IMF) in the collisions of protons (up to 8.1 GeV), ⁴He (4 and 14.6 GeV), and ¹²C (22.4 GeV) on Au has been studied with the 4π setup FASA. In all the cases, thermal multifragmentation of the hot and diluted target spectator takes place. The fragment multiplicity and charge distributions are well described by the combined model including the modified intranuclear cascade followed by the statistical multibody decay of the hot system. IMF-IMF-correlation study supports this picture, giving a very short time scale of the process (≤70 fm/c). This decay process can be interpreted as the first-order nuclear “liquid-fog” phase transition inside the spinodal region. The evolution of the mechanism of thermal multifragmentation with increasing projectile mass was investigated. The onset of the radial collective flow was observed for heavier projectiles. The analysis reveals information on the fragment space distribution inside the breakup volume: heavier IMFs are formed predominantly in the interior of the fragmenting nucleus possibly due to the density gradient.     

Solution of the reduced occupation-number equation for a fermion system

Using the thin target — thin catchers techniques, masses, mean recoil energies and angular distributions of target residues have been measured for 86 MeV/nucleon¹²C induced reactions. Several different nuclear reaction processes, from peripheral to central collisions have been observed. Experimental results are partly reproduced by intranuclear cascade+evaporation calculations. Up to now, the production of the lightest masses (44<A<71) recoiling with high kinetic energies is not correctly understood by theoretical models. More exclusive experiments are needful to check if the formation of a highly excited quasi-compound nucleus could be a possible explanation of the phenomena.     

Emission time of the intermediate mass fragments in collisions of relativistic deuterons with the gold target

The relative velocity correlation function of pairs of intermediate mass fragments has been studied for d + Au collisions at 4.4 GeV. Experimental correlation functions are compared to that obtained by multi-body Coulomb trajectory calculations under the assumption of various decay times of the fragmenting system. The combined approach with the empirically modified intranuclear cascade code followed by the statistical multifragmentation model was used to generate the starting conditions for these calculations. The fragment emission time is found to be less than 40 fm c ⁻¹.     

Low-energy antiproton annihilation in nuclei

The annihilation of 100 MeV antiprotons in atomic nuclei is studied in the frame of an intranuclear cascade model. It is found that the antiproton is annihilated about 1 fm inside the nucleus on the average. The energy released by the annihilation is carried by an average of 5 pions, which cascade throughout the nucleus. About 5% (10%) of the primordial pions are absorbed by the ⁴⁰Ca (¹⁰⁸Ag) target. The pions transfer around 5&#x0303;50 MeV (7&#x0303;00 MeV) to the nucleons and eject about one-fifth of the nucleons. The pion and proton cross sections are calculated. In particular, the relative transparency of the nucleus to high-energy pions (and not to pions in the Δ-resonance region) gives rise to a peculiar pion emission pattern. The time evolution of the baryon density and of the spectrum of the participant nucleons is investigated. It turns out that the cascade does not generate high energy density.     

140A MeV~(40,48)Ca和~(58,64)Ni炮弹碎裂反应产物的统计擦碎模型计算

用统计擦碎模型计算了140AMeV40,48Ca+9Be和58,64Ni+9Be弹核碎裂反应产物的截面.通过对碎片截面计算结果和实验测量结果的比较发现,采用自由空间的核子-核子反应截面计算时,对非中心反应产物的截面拟合很好,而对中心反应产物的截面有较大高估,而采用饱和密度相关的核子-核子反应截面计算时,对非周边反应产物的截面拟合较好,而对周边反应产物的截面有一定程度的低估.在统计擦碎模型中,对核子-核子反应截面进行细致的介质密度关联,可能会改进计算值与实验值的符合程度.     

Angular and energy distributions of grey particles in high-energy hadron-nucleus collisions

The angular and energy distributions of grey particles (mostly protons in the energy range 30–400 MeV) emitted in the interactions of high energy hadrons with nuclei are investigated here. Grey particles “g particles” are assumed to result from the intranuclear cascade initiated by the passage of the incident hadron through the target nucleus. Using the pretested hypothesis that these particles arise only from the first two generations of the cascade, we calculate their angular and energy distributions. Various experimental data are successfully described both in shape and absolute magnitude.     

Cascade particles,nuclear evaporation,and residual nuclei in high energy hadron-nucleus interactions

Based on a Monte Carlo realization of the Dual Parton Model we study the production of target associated particles and of nuclear fragments in high energy hadronnucleus interactions. A formation zone intranuclear cascade of low energy secondaries inside the target nucleus is discussed. We calculate excitation energies of residual nuclei left after the intranuclear cascade process and treat their fürther disintegration by introducing models for the evaporation of protons, neutrons, and light fragments, high energy fission, and by applying a Fermi Break-up model to light nuclear fragments. The results are compared to data on target associated particle production. We fürthermore calculate cross sections for the production of nuclear fragments.