摘要:

We demonstrate that the classical dynamics of a collision between a spherical nucleus and a deformed one at energies near the Coulomb barrier can display chaotic behavior, provided the deformed nucleus is not too heavy. The chaotic scattering is produced by sets of trajectories which are trapped in the potential pocket for a time longer than the one characteristic of a simple spherical symmetric potential scattering. At a semiclassical level this chaotic behavior justifies the presence of Ericson’s fluctuations observed in reactions like28Si+24Mg, while the presence of islands of regular motion embedded in the chaotic region could be the crucial point to explain the nature of the observed isolated resonances. Preliminary results of a full quantal calculation for the same system are also presented.

ISSN:0094-243X    

DOI:10.1063/1.42035

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Experimental evidences for an impact parameter dependence of preequilibrium processes in100Mo+100Mo at 18.67 MeV/u, 23.75 MeV/u and in120Sn+120Sn at 18.34 MeV/u are presented. An incomplete deep inelastic mechanism is proposed. Such a process explains the deviations observed at these incident energies in &sgr;z2−TKEL/1g(for two body) and P3/(P2+P3)−TKEL (for three body) systematics. Model predictions for the preequilibrium emitted nucleons and the corresponding excitation energy per nucleon which remains in the dinuclear system are compared with the experimental data.

ISSN:0094-243X    

DOI:10.1063/1.42011

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The emission of intermediate‐mass fragments (IMFs) from highly excited nuclei is examined as a function of projectile energy. Near threshold the principal IMF sources are (1) the statistical decay of equilibrated composite systems formed in central collisions and (2) peripheral processes which form projectile‐like ejectiles. In the vicinity of the Fermi energy, nonequilibrium IMF emission, presumably from intermediate impact‐parameter collisions, becomes a third important mechanism. At total bombarding energies in excess of 1 GeV, multifragment emission is also observed. In this report we investigate the evolution of these mechanisms as a function of beam energy in both inclusive and exclusive studies of14N‐induced reactions below E/A=100 MeV and3He‐induced reactions up to E/A=1.2 GeV.

ISSN:0094-243X    

DOI:10.1063/1.42012

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The bidimensional Langevin for the symmetric fission of213At were solved without approximations using computer generated stochastic forces. Two dissipation mechanisms have been studied: a typical weak one (hydrodynamical viscosity) and a typical strong one (energy transferred to nucleonic motions from their changing self consistent potential). Calculated transient times (2.10−20sec or less) are comparable with those extracted from measurements of prescission neutron multiplicity. The kinetic energy distribution of the fission fragments was calculated for nuclear temperaturesT=1,2 and 3 MeV. A good agreement between theory and experiment was found for the variation withTof both its mean value and its variance. The calculated absolute values are however slightly lower than the empirical ones. At the same time it was also possible to test the validity of a deterministic (Lagrange) approach to the mean value of the prescission kinetic energy. The error involved was found to decrease with increasingTand to be less than 10%.

ISSN:0094-243X    

DOI:10.1063/1.42013

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In this talk a review on our recent work on fission theory from point of view of diffusion process is presented. The transient phenomena of fission rate are revealed and studied carefully. By comparison of the fission rate calculated both at the saddle and seission points, the latter is emphasized for actual calculation. Our investigation related to the enhancement of the neutron emission prior to fission induced by heavy ion reactions is reported. The quantum aspect of the diffusion model is studied, which is very important for low energy fission. Finally, the extension of one dimensional diffusion model to multi‐dimensional cases is also discussed.

ISSN:0094-243X    

DOI:10.1063/1.42014

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The properties of the GDR in hot nuclei were investigated by measuring high energy &ggr;‐rays in heavy ion fusion reactions. It has been confirmed that the width of the GDR increases rapidly for Ex≥100 MeV and our previously introduced &Ggr;(Ex) can explain the data well for 80≤Ex120 MeV. The limiting temperature of the nucleus for existing of the GDR has been deduced for A∼70, 105 and 130, and it is concluded that the GDR disappears above the temperature of about a quarter of the resonance energy.

ISSN:0094-243X    

DOI:10.1063/1.42015

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The recently discovered phenomenon of DD fusion induced by cluster ion impact on deuterated surfaces is reviewed, along with experimental investigations designed to prove that the phenomenon is not caused by artifacts. Particular emphasis is given to time‐of‐flight experiments which unambiguously establish that the observed fusion events are caused by the slow‐moving cluster ions rather than by faster small‐ion impurities.

ISSN:0094-243X    

DOI:10.1063/1.42017

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

According to the results of the Brookhaven group, d,d fusion can be achieved in deuterated targets when using water clusters, deuterated or not, for energies per unit mass even much below 1 keV. We have investigated the extreme situation of pure deuterium cluster bombardment, choosing a similar range of energy per deuteron in order to make a significant comparison. With such projectiles, magnetically mass selected after acceleration, no fusion event has been detected and our experimental upper limit for the fusion rate was more than two orders of magnitude below the typical values reported with deuterated water clusters. This result supports the picture reported in most of the theoretical models that any favorable energy transfer to the deuterons requires the presence of a heavier collision partner in the projectile. In the course of these experiments, the only possibility for assessing the effect was to use nitrogen instead of deuterium. Unfortunately, only the deflection of the low mass projectiles off the target direction was experimentally feasible. Since fusion was observed both with the pulsed cluster beam and with the continuous leak beam of atomic and molecular species, a contamination by residual deuterons is most likely responsible for the effect.

ISSN:0094-243X    

DOI:10.1063/1.42018

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In order to investigate the role of heavy nuclei in the heavy water cluster impact d+d fusion, we have undertaken a series of d+d fusion experiments using atomic and molecular heavy ions (C, O, Ne, Ar, Kr, and Xe) on the deuterated solid targets in the energy range of 0.4–4 MeV. The observed excitation functions of 3 MeV proton yields are well accounted for in terms of the two step knock‐on cascade model. No distinct differences were observed in d+d fusion rate even when the number of atoms in the oxygen molecule (O+, O2+and O3+) were changed. Extending the calculation of the excitation function of the atomic oxygen impact fusion rate up to the extremely low incident energies (∼keV), it has been found that the estimated proton yields are much smaller than the heavy water cluster impact fusion by 10 orders of magnitude. This indicates that the recent observation of strong enhancement of cluster impact d+d fusion from Brookhaven cannot be explained by the sum of usual elementary processes but must be due to some kind of non‐linear effect.

ISSN:0094-243X    

DOI:10.1063/1.42019

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have investigated deuteron‐deuteron fusion induced by impact of (D2O)n+and (H2O)n+clusters with n=1–150 on deuterated polyethylene targets at energies of 135–225 keV. Both the energy dependence and magnitude of the fusion yield measured with (D2O)115+clusters confirm the results of Beuhler et al. The size dependence of the (D2O)n+fusion yields measured at the impact energy of 225 keV for small (n<10) clusters follow the ‘‘thermonuclear’’ model proposed by Carraro et al. However, for n≳10 the size dependence rapidly deviates to higher yields from the model as n increases. For H2O and (H2O)2+at 225 keV, the yields roughly agree with the ‘‘knock‐on’’ model by Carraro et al. No fusion event was observed for (H2O)n+clusters with n=4–50, however, n=115 clusters produced an observable fusion rate. The ratio between fusion rates of (H2O)115+and (D2O)115+is 5±2%, in close agreement with the result, ∼5%, measured by Beuhler et al. at 300 keV.

ISSN:0094-243X    

DOI:10.1063/1.42020

出版商:AIP    

年代:1992

数据来源: AIP