共查询到20条相似文献,搜索用时 15 毫秒
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《Nuclear Physics A》1987,473(3):564-594
Single- and two-particle inclusive cross sections for light nuclei (p, d, t, 3,4He, 6–9Li, 7,8,10Be) were measured for 14N induced reactions on 197Au at E/A = 35 MeV. At forward angles, θ ≈ 20°, quasi-elastic peripheral reactions and more violent fusion-like collisions were discriminated by measuring the folding angle between two coincident fission fragments resulting from the decay of the heavy reaction residue. More pronounced correlation functions, but very similar emission temperatures are observed for fusion-like collisions as compared to peripheral collisions. 相似文献
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E. Duek L. Kowalski M. Rajagopalan John M. Alexander D. Logan M. S. Zisman Morton Kaplan 《Zeitschrift für Physik A Hadrons and Nuclei》1982,307(3):221-235
Angular and energy correlations have been measured for coincident fission-fragment pairs from the reaction of197Au with 8.6 MeV/u20Ne. These data have been analyzed to test for fission after incomplete fusion and its admixture with fission generally attributed to the relatively pure compound-nucleus mechanism. A Monte Carlo kinematic simulation program has been written to provide a basis for detailed comparisons of the experimental data to the calculations that employ various mechanistic assumptions. We conclude that incomplete fusion is indeed a prominent precursor to fission even for incident energies of less than 10 MeV/u. Similar data from earlier studies have been reanalyzed and shown to be consistent with this conclusion. 相似文献
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G.J. Wozniak G.J. Mathews R.P. Schmitt R. Regimbart H. Hübel R.M. Diamond L.G. Moretto 《Nuclear Physics A》1983,402(2):322-348
Kinetic energy spectra, charge and angular distributions have been measured for thirty elements produced in the reactions of 401 and 460 MeV 56Fe + 197Au and in the reaction of 470 MeV 56Fe + 107, 109Ag. In addition, γ-ray multiplicities were measured at the 470 MeV bombarding energy for both targets at a limited number of angles. The charge distributions for the deep-inelastic component of these systems increase monotonically with atomic number in the measured angular range, whereas, those for the quasielastic component are skewed toward Z-values below the projectile. The angular distributions for the Fe-induced reactions show a smooth evolution from a side-peaked to forward-peaked distributions with increasing mass transfer. This side peak is more intense and more persistent for mass transfers from the projectile to the target. In the quasielastic region the γ-ray multiplicity is observed to increase almost linearly with decreasing Q-value whereas for large negative β-values it is essentially constant and independent of the exit channel mass asymmetry. Finally, angular distributions, angle-integrated charge distributions and γ-ray multiplicities have been compared with a diffusion model in which the dynamics of shape evolution, N/Z equilibration, angular momentum and energy exchange occur via one-body forces. 相似文献
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M. F. Rivet B. Gatty H. Guillemot B. Borderie R. Bimbot I. Forest J. Galin D. Gardes D. Guerreau M. Lefort X. Tarrago B. Tamain L. Novicki 《Zeitschrift für Physik A Hadrons and Nuclei》1982,307(4):365-373
rgy of light charged-particles has been measured in coincidence with one or two fission fragments in the reaction20Ne+197Au at a bombarding energy of 13 MeV/u. The fission cross section was found equal to 1,340±260 mb. Assuming that it represents the totality of the fusion cross section, the critical valuel c is deduced equal to 93±9?, higher thanl Bf=0=74 in the rotating liquid drop model. The main emission source for protons and alpha particles seems to be a thermally equilibrated composite system. The competition between fission and charged particle emission is unexpected in the frame of the statistical treatment. A high energy component is observed in the forward direction. These results correspond to the first step of a study programme on the evolution of nucleus-nucleus collisions between 10 and 100 MeV per nucleon. 相似文献
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Morton Kaplan David J. Moses Dag Ø. Eriksen Mehmet Kildir Douglas R. G. Logan Michael S. Zisman Richard J. McDonald 《Zeitschrift für Physik A Hadrons and Nuclei》1983,313(1-2):31-37
Inclusive4He and4H energy spectra and heavy fragment coincidence correlations have been measured for reactions of 7.31 MeV/u238U with238U and?197Au targets. The H/He production cross sections are in the range 15–26 mb, and their emission spectra are very similar for the two systems. The observed strong kinematic shifts with angle are reproduced in shape and magnitude by Monte Carlo simulations of particle evaporation from projectile-like and target-like fragments, indicating competition between charged particle emission and sequential fission. No evidence is found for high energy charged particle emission associated with ultra-highZ composite systems. Heavy fragment measurements indicate an abundance of quasielastic and deeply inelastic reaction fragments, as well as sequential fission of target and projectile nuclei. For238U nuclei, the fission occurs predominantly in an asymmetric mode, reminiscent of fission at low excitation energy. For238+238U reactions in the vicinity of the grazing angle, the frequency of single sequential fission (with survival of the partner fragment) is twice as large as double sequential fission in which both the target and projectile undergo fission. In238U+197Au reactions, the survival probability of the heavy fragments is even greater. The surprisingly high survival probabilities of high-Z fragments imply a preponderance of very soft collisions in these very-heavy-ion reactions, at least at energies not very far over the Coulomb barrier. 相似文献
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《Nuclear Physics A》1997,620(2):214-228
Two-particle correlation functions were measured for the emission of protons, deuterons, tritons, α, and lithium fragment at small relative momenta in 40Ar-induced reactions on 197Au at 25 MeV/nucleon. Based on three-body trajectory calculations the emission time scales for the particles were extracted from p-d, d-d, t-t, and lithium-lithium correlation functions. The mean emission time was found to decrease with increasing sum of the kinetic energies of the particle in a correlated pairs, indicating the emission of more energetic particles at earlier stages of the reaction than at later stages. The time scale for the emission of lithium fragments emission suggests that sequential binary disassembly occurs in 40Ar+197Au reaction at MeV/nucleon. Mean emission temperature of 3.5−0.8+1.3 and 3.6±0.4 MeV were also extracted from the relative populations of the excited and ground states of the respective emitted nuclides 8Be and 4He. 相似文献
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E. Funke G. Wirth J. V. Kratz W. Brüchle Fan Wo K. Sümmerer 《Zeitschrift für Physik A Hadrons and Nuclei》1997,357(3):303-316
Differential cross sections as a function of cm angle were measured for 1n- and 2n-transfer reactions in 238U + 197 Au and197 Au + 197 Au collisions in the energy range from 0.881 Vc to 1.093 Vc and 0.825 Vc to 0.964 Vc, respectively. For 198Au and 199Au from the 238U + 197Au collisions, for reduced distances of closest approach d o 1.55 fm, the angular distributions at all bombarding energies are well described by the semiclassical theory. Equivalently, the transfer probabilities show the expected exponential decrease with increasing d o over many orders of magnitude. For all other transfer products from 238U + 197Au collisions, and for all transfer products from 197Au + 197Au collisions, markedly reduced cross sections relative to the semiclassical theory are observed for central collisions at all bombarding energies, even for values of d o that are well outside the region where absorption is known to set in. Only for the more peripheral collisions, one observes agreement of the angular distributions (transfer probabilities) with the semiclassical expectations. The deviations for central collisions are absent for reactions with positive Q gg values and scale roughly with increasingly negative values of Q gg, i.e. with increasing Q-value mismatch. Channel coupling is proposed as the relevant mechanism. 相似文献
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A. Fahli J. P. Coffin G. Guillaume B. Heusch F. Jundt F. Rami P. Wagner P. Fintz A. J. Cole S. Kox Y. Schutz N. Cindro 《Zeitschrift für Physik A Hadrons and Nuclei》1987,326(2):169-177
The light charged particles emitted in the40Ar+68Zn reaction performed at 14.6, 19.6 and 35 MeV/nucleon have been studied inclusively. The energy spectra have been analysed in terms of preequilibrium emission, moving source and coalescence models. A complete coherence between the present data and those obtained separately from heavy fragment studies is achieved. These data are consistent with the onset of projectile fragmentation between 20 and 35 MeV/nucleon correlated with the formation of a highly excited region of the nuclear system inducing light particle emission. The other sources of light particles can be interpreted as statistical and sequential decay of the quasi projectile. 相似文献
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E. Duek L. Kowalski M. Rajagopalan J. M. Alexander T. W. Debiak D. Logan M. Kaplan M. Zisman Y. LeBeyec 《Zeitschrift für Physik A Hadrons and Nuclei》1982,307(3):237-245
Measurements are reported for correlated energies and angles of heavy fragments from reactions of 343 MeV40Ar with197Au. The results show a continuous evolution of the mass distributions from fission-like products at angle pairs of ≈60 and 300 degrees to deeply inelastic projectile-like products at ≈45° and 300°. Certain difficulties are emphasized for the use of the “symmetric fragmentation” cross sections in the context of current theoretical models (e.g. the “extra push” theory). The fission-like reactions have been studied in some detail and the results have been compared to a Monte Carlo kinematic simulation. To account for the experimental results forward-peaked light particle emission (n, H, He) must occur in a large fraction of the fission-like reactions. 相似文献
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Light charged particles emitted in heavy-ion induced reactions, their spectra and angular distributions measured over a range
of energies, carry the signature of the underlying reaction mechanisms. Analysis of data of light charged particles, both
inclusive and exclusive measured in coincidence with gamma rays, fission products, evaporation residues have yielded interesting
results which bring out the influence of nuclear structure, nuclear mean field and dynamics on the emission of these particles. 相似文献
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B. Borderie M. F. Rivet C. Cabot D. Fabris D. Gardès H. Gauvin F. Hanappe J. Péter 《Zeitschrift für Physik A Hadrons and Nuclei》1984,318(3):315-321
Angular and energy distributions have been measured for products of 4≦Z≦12 from reaction of 1,095 MeV40Ar+natAg. In addition to sources located near the projectile and fusion system velocities, the data show the presence of a source located aroundV beam/2 which cannot be explained by any existing model. A possible interpretation is proposed. 相似文献
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L. Schad H. Ho G. -Y. Fan B. Lindl A. Pfoh R. Wolski J. P. Wurm 《Zeitschrift für Physik A Hadrons and Nuclei》1984,318(2):179-190
Energy and angular correlations between alpha particles and fission-like fragments in the reaction of35Cl+Ag at 10 MeV/n have been measured. The coincident yield is dominated by two mechanisms: sequential emission from both fragments (M α =0.137±0.014) and alpha emission from the composite system prior to scission (M α =0.124±0.012). The observation of nuclear shadowing for sequential emission from the fragments allowed us to estimate the “lifetime” of the 218 MeV excited143Gd composite system as (1–3)×10?20s. It is argued that this rather long time reflects the slow evolution in shape of the composite system and might be termed “sticking time,” since statistical-model lifetimes are typically an order of magnitude shorter. Observed also are small contributions of nonequilibrium emission in the forward direction (M α =0.005±0.001) and a component displaying the characteristics of emission from the neck (M α =0.010±0.002). 相似文献
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N. N. Ajitanand John M. Alexander H. Delagrange E. Duek D. Ø. Eriksen D. Guerreau Morton Kaplan M. Kildir L. Kowalski R. Lacey D. Logan D. J. Moses G. F. Peaslee Louis C. Vaz M. S. Zisman 《Zeitschrift für Physik A Hadrons and Nuclei》1984,316(2):169-176
Multiplicities are compared for4He evaporation in reactions of40Ar and56Fe projectiles (8.5 MeV/u) with withnatAg and238U targets. Coincidence requirements involving fusion-fission and projectile-like fragments have been used to select separate entrance-channel spin zones. Evaporation-like4He emission from the composite nuclei is shown to be large for mean spins ≦100?, and to decrease dramatically with increasing spin. Coincidence measurements between two4He particles have also been studied for40Ar+natAg. This requirement is shown to select reactions that lead to evaporation residues and therefore to a zone of relatively low spin. The shapes of the4He spectra provide an interesting probe of the mechanism and also of the thermodynamic properties of hot nuclei. 相似文献
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The characteristics of fragment emission in peripheral 197Au+197Au collisions 35 MeV/A are studied using the two clusterization approaches within framework of quantum molecular dynamics model. Our model calculations using minimum spanning tree (MST) algorithm and advanced clusterization method namely simulated annealing clusterization algorithm (SACA) showed that fragment structure can be realized at an earlier time when spectators contribute significantly toward
the fragment production even at such a low incident energy. Comparison of model predictions with experimental data reveals
that SACA method can nicely reproduce the fragment charge yields and mean charge of the heaviest fragment. This reflects suitability
of SACA method over conventional clusterization techniques to investigate spectator matter fragmentation in low energy domain. 相似文献
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《Nuclear Physics A》1987,464(1):172-188
Peripheral reactions induced on 92Mo,98Mo, natAg and 197Au targets by 22 MeV per nucleon krypton beam were studied. Fragments observed with velocities close to the beam velocity can be interpreted as coming from a quasi-fragmentation of the projectile. The isotopic distributions measured for the fragments produced with the Kr projectile reflect some influence of the composite system. Thus it seems that projectile fragmentation is not the only mechanism involved in these reactions and that the mean field interaction still plays an important role at this energy. 相似文献
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M. Sowiński M. Lewitowicz R. Kupczak A. Jankowski N. K. Skobelev S. Chojnacki 《Zeitschrift für Physik A Hadrons and Nuclei》1986,324(1):87-95
The results of coincidence measurements of4He emission with fission fragments in reactions of12C(108 MeV) ions with a197Au target and of16O(144 MeV) ions with a232Th target are presented. On the basis of a Monte Carlo kinematic simulation of nuclear reactions the experimental energy spectra and velocity distributions of alpha particles have been analyzed. A conclusion has been drawn that the main source of4 He emission is evaporation from the fissioning compound nucleus. Substantial part of alpha particles was emitted from fully accelerated fission fragments. Some of4He nuclei with an average energy of about 16 MeV (in the CM system) emitted mainly perpendicular to the fission axis were identified as being similar long-range alpha particles produced in ternary fission of heavy nuclei at a low excitation energy. The emission multiplicities of these particles are considerably higher than those observed at a low excitation energy. The experimental results are compared with the statistical model predictions. 相似文献