共查询到20条相似文献,搜索用时 11 毫秒
1.
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
2.
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
3.
The mass number distributions of three fragments from the ternary fission of the system 197Au+197Au are reproduced rather well by using the improved quantum molecular dynamics (ImQMD) model without any adjusting parameter. It is found that the probability of ternary fission evidently depends on the incident energy and the impact parameter, and the two-body dissipation is the main mechanism responsible for the formation of the third fragment with comparable mass. 相似文献
4.
Calculations are presented of the elastic scattering and fusion cross sections for the astrophysically interesting reactions 12C+12C, 12C+16O and 16O+16O. The calculations are performed using the incoming wave boundary condition (IWB) and a real ion-ion interaction potential. The results are compared with the available experimental data for the energy region near and below the Coulomb barrier. With values of two adjustable potential parameters (the radial position of the l = 0 barrier and the diffuseness) determined by fitting elastic scattering data, good agreement is obtained for the average energy dependence of the 12C+12C and 12C+16O fusion cross sections. In the case of 16O+16O, both the calculated absolute magnitude and the energy dependence of the fusion cross section are inconsistent with the data and this discrepancy is discussed. 相似文献
5.
G. Hulke C. Rolfs H. P. Trautvetter 《Zeitschrift für Physik A Hadrons and Nuclei》1980,297(2):161-183
The partial cross sections of heavy residual nuclei produced in the heavy ion fusion of12C+20Ne have been measured atE c.m.=6–15 MeV viaγ-ray spectroscopy with a Ge(Li) detector. Windowless and recirculating gas target systems have been used. The dominant residual nuclei are24Mg,27Al,28Si,30Si,30P and31P, which arise from two- and three-body breakups in the exit channels. The observed excitation functions are smooth in their energy dependence and give no indications for the existence of pronounced resonance structures, in contrast to theoretical predictions. The Coulomb excitation of20Ne served as an intrinsic calibration standard in the determination of absolute partial and total fusion cross sections. The same experimental set-up was also used in the reaction studies of16O+16O atE c.m.=7–14 MeV, going through the same compound nucleus32S at similar excitation energies. The observed energy dependence in the excitation functions is in good agreement with previous work. The total fusion cross section agrees fairly well with two sets of values reported previously, but deviates significantly from other reported absolute cross section values. The relative evaporation distributions of the residual nuclei are similar for both heavy ion reactions. However, the ratio of their total fusion cross sections deviates from model predictions and suggests that compound nucleus formation does depend on the microscopic structure of the colliding nuclei in the entrance channel. From the observed energy dependence of the above ratio, particularly at subcoulomb energies, geometrical effects in the entrance channel (due to deformed and spherical nuclei) appear to be weak. The astrophysical aspects of the data in the context of late stellar nucleosynthesis are discussed. 相似文献
6.
H. G. Bohlen E. Stiliaris B. Gebauer W. von Oertzen M. Wilpert Th. Wilpert A. Ostrowski Dao T. Khoa A. S. Demyanova A. A. Ogloblin 《Zeitschrift für Physik A Hadrons and Nuclei》1993,346(3):189-200
Elastic, inelastic scattering as well as one-neutron transfer channels have been measured over a wide angular range for systems16O+16O at the incident energy of 350 MeV and20Ne+12C at 390 MeV, respectively, using the Q3D magnetic spectrometer. In both cases differential cross sections have been measured down to about 50 nb/sr (or d/d
R10–4) at large angles. For the16O+16O system refractive contributions are found at the level of these cross sections, whereas in the20Ne+12C case a steeper decrease of the differential cross section with the angle is observed and the refractive contribution can not be determined. The elastic scattering data have been analyzed using standard Woods-Saxon potentials and potentials calculated in different versions of the double-folding model. Some properties of these potentials are tested in the calculations for inelastic scattering and one-neutron transfer within the DWBA. With the refractive pattern observed for the16O+16O system, the scattering and transfer data are found to be sensitive to the interaction potential at small internuclear distances down to about 2.5 fm.It should be acknowledged that part of the folding analysis reported here was done while one of the authors (D.T.K.) was staying at the Institute for Theoretical Physics, University of Tübingen. We also thank Prof. H. Clement and H. Abele for numerous discussions and contributions and Prof. G.R. Satchler for helpful comments on the use of the DWBA code PTOLEMY. 相似文献
7.
M. Y. H. Farag 《Acta Physica Hungarica A》1997,5(2):117-126
The statistical scission model is applied to study the mechanism of multifragmentation of heavy ions induced fission. The Carbon-Oxygen reactions sequentially producing seven alpha particles are studied. Effective variances together with cross sections for alpha particles emitted from these reactions are calculated at different incident energies ranged from 70 MeV up to 350 MeV. The obtained results are in good agreement with previous sequential emission of alpha particles fission model calculations. 相似文献
8.
J. Łukasik G. Auger M. L. Begemann-Blaich N. Bellaize R. Bittiger F. Bocage B. Borderie R. Bougault B. Bouriquet J. L. Charvet A. Chbihi R. Dayras D. Durand J. D. Frankland E. Galichet D. Gourio D. Guinet S. Hudan P. Lautesse F. Lavaud A. Le Fèvre R. Legrain O. Lopez U. Lynen W. F. J. Müller L. Nalpas H. Orth E. Plagnol E. Rosato A. Saija C. Schwarz C. Sfienti B. Tamain W. Trautmann A. Trzciński K. Turzó E. Vient M. Vigilante C. Volant B. Zwiegliński 《Acta Physica Hungarica A》2006,25(2-4):229-239
Directed and elliptic flow for the 197Au+197Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4π multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the σ NN and demonstrate the importance of angular momentum conservation in transport codes at low energies. 相似文献
9.
The 16O + 9Be reactions have been studied from Ec.m. = 2.0 MeV to 5.1 MeV, an energy near the top of the Coulomb barrier. The cross section for the neutron transfer reaction 9Be(16O,17O1 (0.87 MeV))8Be has been measured over this range by detecting the prompt 0.87 MeV γ-rays. The total fusion cross section has been determined from Ec.m. = 2.8 to 5.1 MeV by observing individual γ-ray transitions in the evaporation residues with a Ge(Li) detector, and then summing the separate yields. Direct processes are found to dominate the reaction yield below Ec.m. = 4 MeV. A comparison of the energy dependence of the fusion cross section for this reaction and the 12C + 13C reaction, which proceeds via the formation of the same compound nucleus, 25Mg, reveals differences at sub-barrier energies. Optical model and incoming-wave boundary condition calculations are presented. Data have also been obtained for the near optimum Q-value neutron-transfer reactions 9Be(12C, 13C1)8Be and 9Be(19F, 20F)8Be, and these are discussed in terms of a simple model of sub-barrier direct reactions. 相似文献
10.
A barrier-top-resonance model calculation is found adequate to describe the gross structure behavior thus far observed in inelastic scattering excitation functions. 相似文献
11.
B. S. Tomar A. Goswami A. V. R. Reddy S. K. Das P. P. Burte S. B. Manohar Satya Prakash 《Zeitschrift für Physik A Hadrons and Nuclei》1992,342(2):223-227
Excitation functions for the evaporation residues for the reactions12C+93Nb and16O+89Y in the projectile energy range of 4 to 6.5 MeV/amu have been measured using off-line gamma spectrometry. The excitation functions for neutron(xn), proton(pxn) and one alpha(xn) emission channels are practically similar for both the reactions. However the products formed by two alpha(2xn) emission show much higher cross sections in the12C+93Nb than the16O+89Y system. This has been explained in terms of the incomplete fusion process involving transfer of an alpha particle from the projectile to the target in the former case.Authors thank Shri D.C. Ephraim for making the rolled metal foils and the operation crew of PELLETRON facility for their help in carrying out the irradiations. Authors are grateful to Dr. P.R. Natarajan, Head Radiochemistry Division for his keen interest in this work. 相似文献
12.
The elastic scattering of12C+12C and16O+16O has been studied in the framework of an incoming wave boundary condition model. Different logarithmic derivatives for the incoming waves have been tested and their effects investigated with the help of Fourier analyses. It is shown that a logarithmic derivative obtained from a JWKB approximation leads to strong absorption of the low partial waves while a logarithmic derivative constant for all partial waves causes reflections. These reflections are necessary to describe the high energy elastic scattering of12C+12C. The fits thus obtained with shallow real potentials are comparable to those obtained with deep folding potentials. It is shown that not the lowest partial waves, but those within a window just below the grazing angular momentum are most important for the higher energy12C+12C angular distributions. 相似文献
13.
14.
T.R. Todd C.M. Clayton W.B. Telfair T.K. McCubbin J. Plíva 《Journal of Molecular Spectroscopy》1976,62(2):201-227
The combination of a new high-resolution grating spectrometer and a spontaneous emission source has made it possible to measure precisely the 1 → 0, 2 → 1, and 2 → 0 transitions of 12C16O relative to the accurately known 12C16O laser lines which have been referred to pure frequency standards by Eng et al. The 1 → 0 and 2 → 0 band centers agree to within 0.0002 cm?1 with those measured relative to wavelength standards by Fourier transform spectroscopy (FTS). From a weighted simultaneous fit to the FTS-absorption, FTS-flame, our grating-emission, and microwave results, a set of calculated line positions was obtained for the 1 → 0, 2 → 1, and 2 → 0 transitions of 12C16O. The absolute accuracy of these line positions is believed to be ±0.0005 cm?1 and we propose that the lines can be used as secondary wavenumber standards in the infrared.The spontaneous emission sequences v′ → (v′ ? 1) were measured for 12C16O up to v′ = 20, for 13C16O up to v′ = 11 (using a 13C-enriched sample), and for 12C18O up to v′ = 4 (in natural abundance). Internally consistent sets of Dunham coefficients were calculated from the best available data for the molecules of 12C16O, 13C16O, and 12C18O. 相似文献
15.
H. Ikezoe N. Shikazono Y. Tomita Y. Sugiyama K. Ideno W. Yokota Y. Nagame S. M. Lee M. Ogihara S. C. Jeong H. Fujiwara D. J. Hinde 《Zeitschrift für Physik A Hadrons and Nuclei》1988,330(3):289-293
Mass distributions of fission fragments have been measured for the reaction of19F on197Au as a function of scattering angle. The mean fragment mass is dependent on the scattering angle, the asymmetry increasing with increasing projectile energy. 相似文献
16.
Production of heavy fragments in the fission mass region in C+U, Bi, Au and Ag reactions at 26.5 GeV
Formation of heavy fragments in the fission mass region in the interaction of 26.5 GeV with U, Bi, Au and Ag is studied using a sandwich configuration of the Makrofol polycarbonate track detector. Events in which at least one heavy fragment in the fission mass region is detected are analyzed. Fragments produced in these events are identified and an event-by-event model-free analysis is performed in order to separate different production mechanisms. We have identified the events produced in fission, deep spallation and fragmentation processes. The cross sections and experimental features are determined for these reaction mechanisms, and their variations as a function of the target mass have been investigated. The results show that in the interactions of with U the dominant process is fission, while in the interactions of with lighter target nuclei the dominant processes are deep spallation and fragmentation. 相似文献
17.
18.
Absolute cross sections have been measured for the reactions 10B(16O, 6Li)20Ne and 12C(14N, 6Li)20Ne at several energies in the range Ec.m. = 7.5–16.2 MeV, and 13.8–16.6 MeV, respectively. The predictions of Hauser-Feshbach calculations show generally good agreement with the experimental data without parameter variation. The consequences of an angular momentum cutoff in the entrance channel and in the compound nucleus are discussed. 相似文献
19.
N. Ikeda F. Nakamura K. Mizuuchi T. Sugimitsu S. Teruyama T. Okamoto H. Fujita S. Morinobu 《The European Physical Journal A - Hadrons and Nuclei》2000,7(4):491-502
The 16O(13C,12C)17O reaction at 50 MeV has been investigated using the kinematical coincidence method. Polarization tensors t
20 and t
40 of 12C[2+
1] for the quantization axis taken along the direction of propagation have been measured by analyzing the energy spectrum of
12C[2+
1], modulated by the effect of γ ray emission. The deduced t
40 values significantly deviate from zero, contrary to the prediction of the distorted-wave Born approximation theory based
on one-step p shell neutron stripping without spin-dependent interactions. The phenomenological spin–orbit interaction necessary
to reproduce the magnitude of measured t
40 is found to be much larger than the folding model prediction. It is shown that the experimental polarization tensors as well
as the cross sections can be reproduced by introducing multi-step processes involving excitations in 12C and 13C without introducing spin-dependent interactions.
Received: 2 August 1999 / Revised version: 3 February 2000 相似文献