Study of a fast collective mode in deep inelastic reactions: Quantal fluctuations

We have measured for the 430 MeV⁸⁶Kr+^92.98Mo systems the triple differential cross sectiond ³ σ/dEdAdZ (E=kinetic energy,A=mass andZ=atomic number) of the reaction products in the angular range (θ=25, 45°). We focussed attention on a fast collective mode in deep inelastic reactions: the neutron excess or charge equilibration. This mode is shown to relax very quickly to equilibrium within a time scale of the order of 10^?22s. It is shown that this collective degree of freedom exhibit a quantal behavior which can be seen in the observation of quantal fluctuations. The experimental results are discussed in terms of a simple equilibrium model. The giant dipole resonance of the composite system could be closely connected to this neutron excess mode.     

Neutron multiplicities in inelastic collisions of132Xe with197Au

Neutrons have been detected in coincidence with charged reaction products in inelastic scattering of 7.5 MeV/u¹³²Xe ions from¹⁹⁷Au. The deduced neutron multiplicities associated with the heavy and light fragment, respectively, are roughly proportional to the total kinetic energy loss, and their ratios are close to the Au-Xe mass ratio for allQ-values. These results and the measured neutron energy spectra are consistent with the assumptions of thermal equilibrium between the fragments at scission, and of neutron emission from fully accelerated fragments. For deep inelastic events, the measured absolute multiplicities are smaller than expected from statistical model calculations, but an effect due to pre-equilibrium emission of particles — as suggested by an earlier analysis of the present data [1] — cannot be definitely established.     

Analysis of the sequential fission observed in collisions of100Mo +100Mo and120Sn +120Sn around 20 A·MeV

Events with 2, 3 and 4 heavy fragments (A≥20) detected in the reactions¹⁰⁰Mo +¹⁰⁰Mo at 18.7, 23.7 A·MeV and¹²⁰Sn +¹²⁰Sn at 18.4 A·MeV were analyzed by means of an improved version of the kinematic coincidence method. The phase-space distributions prove that 3- (and possibly 4-) body events predominantly originate from a two-step mechanism and are compatible with the hypothesis of a binary deep-inelastic interaction followed by the further fissionlike decay of one (or both) of the primary fragments. The characteristics of the fission step — mass asymmetry, relative velocity, in-plane and out-of-plane angles — have been reconstructed for the 3-body events and indications are found that nonequilibrium effects at the end of the deep-inelastic phase may influence the fissionlike decay.     

Nebenreaktionen bei der Umsetzung von Trimethylsilylazid mit Trimethylphosphit und Trisdimethylaminophosphin

Side Reactions upon Interaction of Trimethylsilyl Azide with Trimethylphosphite and Trisdimethylaminophosphine Trisdimethylaminophosphine reacts with trimethylsilyl azide with evolution of nitrogen and formation of N-trimethylsilyl-iminophosphoric acid hexamethyltriamide, (Me₂N)₃ · P ? N? SiMe₃. The diphosphazene (Me₂N)₃P ? N? P(NMe₂)₂ ? N? SiMe₃ is formed in a side reaction with concomitant elimination of dimethylamino trimethylsilane. The reaction of trimethylsilyl azide with trimethylphosphite affords, besides the expected N-trimethylsilyliminophosphorus trimethylester, (MeO)₃P ? N? SiMe₃, the isomeric N-trimethylsilyl-N-methyl-aminophosphoric dimethylester, (MeO₂)P(O)? N(Me)SiMe₃.     

Evidence for multiphonon giant resonances in electromagnetic fission of 238U

Differential cross sections for electromagnetic fission of 238U projectiles (500 MeV/u) in C, Sn, and Pb targets are measured and analyzed in terms of single- and multiphonon giant resonance excitations as doorway states to fission. A novel experimental method exploits the linear relationship between neutron multiplicity and the primary 238U excitation energy. Multiphonon states contribute up to 20% of the cross section; a component at high excitation energies is indicated that may arise from three-phonon dipole and two-phonon GDR x GQRiv giant resonance excitations.     

Optical levitation of absorbing particles with a nominally Gaussian laser beam

We use a Gaussian laser beam to study the levitation of absorbing Mie particles. Several metal oxide particles are stably levitated, and their movement over time is recorded. Our studies show that the position of each particle is highly dependent on the other particles' locations. The observations are explained by the phenomenon of thermal creep. The increased local pressure that is due to a temperature gradient along the particle's surface induces levitation. The particles rest close to minima in the intensity distribution near the optical axis. An experiment is suggested that can be used to locate these minima in a laser beam.