Mass and charge flow in the reaction 7.1 MeV/u197Au+63Cu

Mass-yield and angular-distribution data are presented for products from the reaction of 7.1 MeV/ ¹⁹⁷Au with⁶³Cu. With help from information derived from the latter, the former are classified into components corresponding to quasielastic transfer (580±80 mb), deep-inelastic transfer plus quasifission (1300±130 mb), fusionfission (195 mb), and sequential fission (195±45 mb). The fusion excitation function calculated with the Dynamic Capture model standard parameter set reproduces our deduced fusion-fission cross section well. Moreover, using this cross section as well as additional published data for the same reaction system, we extract ans-wave fusion-barrier shift (extra push) for this system of 35±7 MeV, which is in good agreement with the systematics derived from other fusion-barrier shifts which have been reported in the literature. Lastly, support is found for the Dissipative Diabatic Dynamics model prediction that dynamically-hindered fusion trajectories are reflected into quasielastic channels.Research supported by the Bundesministerium für Forschung und Technologie under contract number 06 MR 553     

The reaction238U +238U at 7.42MeV/u

One-particle-inclusive measurements have been performed for the charge, kinetic energy and angular distributions of reaction products from²³⁸U +²³⁸U at 1 766MeV (7.42MeV/u) incident energy. The deep inelastic products exhibit features similar to those seen in reactions induced by medium heavy nuclei: increasing particle transfer is observed with increasing energy damping, the angular distributions are peaked near the grazing angle, they broaden significantly with increasing energy loss and/or charge transfer. The dominant reaction mechanism, however, is found to be sequential fission of one or both primary reaction products. The reconstructed primaryZ- andQ-value distributions show more particle transfer at a given energy loss than in other systems, i.e. the diffusion process seems to proceed colder in this system. This is confirmed by relatively large cross sections for surviving deep inelastic reaction products belowZ=92. A direct search forα-decay or fission of superheavy nuclei being produced in a deep inelastic reaction and being implanted in a surface barrier detector resulted in an upper cross section limit of 2 ×10^?32cm².     

Hard photon production in the reaction Xe+Sn at 50 A MeV

The first results of the analysis of the TAPS experiment performed at GANIL in 1998 are presented. First, the pre-analysis of a typical TAPS experiment (data storage, energy calibration, time alignment, time monitorings and pulse-shape analysis) is described. Secondly, a preliminary inclusive hard photon spectrum of the reaction ¹²⁹Xe+¹¹²Sn at 50 A MeV is shown. The hard photon spectrum exhibits a good agreement with the systematics collected by the TAPS collaboration in the last KVI experiments.     

High-energy fragments produced in the84Kr+93Nb reaction at 34.5 MeV/u

We have studied the heavy-ion capture reaction⁹Be(¹²C,γ)²¹ Ne at E_CM=3.5–6.6 MeV and Θ = 90. High-energyγ-rav decay to the low-lying states of²¹Ne was observed, even well below the Coulomb barrier.     

Fragment correlations in the reaction 9.03 MeV/u238U+natU

Kinematically almost complete correlation studies on heavy fragments in the reaction 9.03 MeV/u²³⁸U+^natU were performed using metaphosphate-glass detectors in a 2π-geometry technique. Absolute data for the total reaction cross-section and the partial cross-sections for the three-, four-, and five-body reaction channels were measured. The tracks of correlated particles were measured and converted into masses and energies. The reaction mechanism of each individual event was studied in terms of the separation velocities of correlated fragment pairs. Sequential fission following inelastic collision is found to account for all analysed events with more than two heavy nuclei in the exit channel. The masses, scattering angles, and energies of the first reaction step were reconstructed event by event.     

Moments of charge distributions in the reaction92Mo+92Mo at 14.7 MeV/u

First and second moments of primary charge distributions were determined as a function of the total kinetic energy loss in the reaction⁹²Mo+⁹²Mo at an incident energy of 14.7 MeV/u. Up to energy losses of 200 MeV no significant drift of the first moments is observed. The second moments are in agreement with predictions of a stochastic model derived at lower bombarding energies.     

The reaction mechanism in the system132Xe+56Fe at 5.73 MeV/u: Evidence for a new type of strongly damped collisions

We present data for the¹³²Xe+⁵⁶Fe-system at 5.73 MeV/u laboratory energy. Due to inverted kinematics, where Xe is the projectile, we were able to measure energy spectra as well as angular distributions for reaction products with 20≦Z≦60 with unitZ-resolution; i.e. target- and projectile-like fragments have been investigated. The reaction shows a well focussed quasielastic component, where charge transfer from the light to the heavy collision partner dominates. This apparent tendency towards more asymmetric fragmentation is explained by a potential energy surface which favours such charge transfer in order to minimize the asymmetry energy of the liquid drop. The strongly damped component which constitutes the major part of the reaction cross section exhibits characteristics of a fusion-fission reaction with typical fission fragment kinetic energies and 1/sinΘ _c.m. angular distributions. The maximum cross section is found for the symmetric fragmentation, no clear indication is observed for a diffusion process leading to target- and projectile-like fragments. Our data are difficult to reconcile either with the standard diffusion models or with an equilibrated compound nucleus fission picture. We tentatively conclude that an essential part of the fully damped cross section originates from partial waves for which the compound nucleus has no fission barrier.     

Resonant electron transfer andL-shell excitation at 3.6 MeV/u Smq+→Xe collisions

Resonance energies and widths of four resonances in the reaction²⁵Mg(p,γ)²⁶Al were measured with the high resolution proton beam of the new 500 kV accelerator IONAS. The previously given large width of the 389 keV resonance, Γ= 460±70 eV. (1), used in the interpretation of stellar²⁶A1 production was shown to be incorrect and probably caused by target oxidation effects and insufficient energy resolution of the beam. The new value is Γ<4 eV.     

Fission study for the system84Kr+232Th at 25, 35 and 45 MeV/u

Recoil velocities of heavy residues produced in the bombardment of⁸⁴Kr beams on a²³²Th target at energies about the Fermi velocity were determined using the method of correlations between fission fragments. The masses of both fragments were also measured. The data show events with high recoil velocity which are produced in incomplete fusion processes. Estimates of the energy transfer are given. Comparisons with incomplete fusion data obtained with other projectiles in the same incident velocity range show an increase of the energy transfer with the mass of the projectile.     

On-line γ-ray investigation of the14N+27Al reaction at 30 MeV/u

The cross-sections of target-like residues following the¹⁴N+²⁷Al reaction at 30 MeV/u have been measured from in-beam and radioactiveγ-ray spectra. The recoil velocities of some fragments have been estimated from theγ-ray Doppler broadening.     

Approaching peripheral collisions in the reaction Ar+Au at 27.2 MeV/u by the associated neutron multiplicities

A 4π detector has been used to measure the neutron multiplicity associated with peripheral heavy ion reactions induced at 27.2 MeV/u. A strong correlation is observed between the number of emerging neutrons and the mass of the projectile-like-fragment. However, the large energy dissipation which is observed is still too small to support the idea of a pure massive transfer process.     

Investigation of the Kr + Au system at 22 MeV/u

With laser-atomic-beam-spectroscopy the hyperfinestructure splitting constants A, B and the lifetimes τ of the Mn I levels 3d⁵4s4p z⁴p_3/2,5/2 were determined from the UV intercombination lines 321,7 nm and 322,5 nm. We obtained: A=?821(3)MHz, B=?40(30)MHz, τ=1120(50)nsec for the J=3/2 level and A=?607,8(1,5)MHz, B=+75(15)MHz, τ=970(50)nsec for the J=5/2 level.     

Knockout reaction induced by ~6 He at 61.2 MeV/u

A knockout reaction induced by ⁶He at 61.2 MeV/u was carried out at the HIRFL-RIBLL radioactive beam line. The α core fragments at forward angles were detected in coincidence with the recoiled protons at large angles. From this coincident measurement the valence nucleon knockout mechanism and the core knockout mechanism can be separated according to the polar angle correlation between the core fragments and the recoiled protons. It is demonstrated that, when reconstructing the resonant state of a weakly bound nucleus, the contamination resulting from the core knockout mechanism should be eliminated in order to obtain the correct structure information.     

15.14MeV/u 136Xe离子引起的单粒子效应

研究了15.14MeV/u ¹³⁶Xe离子在不同批次的32k×8bits静态存储器中所引起的单粒子效应.获得了单粒子翻转和单粒子闭锁截面与入射角度的依赖关系.将单粒子效应截面与灵敏区中沉积的能量相联系,而不是线性能量转移(LET)值.估计了灵敏体积的深度和死层的厚度.     

A Semi-exclusive study of heavy-residue production in the40Ar + Ag reaction at 35 MeV/u incident energy

Heavy residues created in the reaction Ar + Ag at 35 MeV/u have been detected at various forward angles. Their velocity spectra (quite different from the corresponding spectra measured at 27 MeV/u) show that these events result both from central and peripheral reactions and that the fusion component has dramatically decreased. Coincident light charged particles spectra have been obtained in a large solid angle forward hodoscope. The analysis of these spectra allows to differentiate peripheral and central collisions. The proton spectra are analysed in terms of emitting sources. There is no need for a participant zone in peripheral reactions. Instead protons are emitted either from the target like or from the projectile like fragments. However projectile sequential emission is not sufficient to explain all the high energy protons.     

晕核6He（25 MeV/u）在9Be上的破裂反应

25 MeV/u 6He+9Be反应的实验中利用多个探测器望远镜对反应产物进行了测量, 对实验中各个角度测量到的4He进行观察, 将其中两个有高能峰成分的探测器划分成三部分, 得到不同角度4He的单举能谱和破裂产生4He的微分截面. Different products of 6He nuclei from 9Be target has been measured with a 6He beam at energy of 25 MeV/u. The energy spectra at different angles for 4He isotope were analyzed and the experiment differential cross sections for the direct breakup reaction were obtained.     

Binary break-up of a high-velocity hot source formed in the 84Kr+93Nb reaction at 34.5 MeV/u

The fragment production in the ⁸⁴Kr+⁹³Nb reaction at 34.5 MeV/u has been investigated by coincidence measurements. The observed fragment-fragment and fragment-particle correlations can be explained by a binary break-up of a high-velocity source having about 90% of the beam velocity and formed by a deep interaction between the projectile and the target.     

Light fragments produced in40Ar+natAg reactions at 27MeV/u

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.