Transverse momentum distributions of neutral pions from central and peripheral16O+Au collisions at 200A·GeV

The production of neutral pions by the interaction of 200A·GeV p and¹⁶O projectiles with a Au target has been studied in the pseudorapidity range 1.5≦η≦2.1. Transverse momentum spectra have been measured between 0.4 GeV/c and 3.6 GeV/c and their dependence on the centrality of the collision has been investigated. The peripheral-collision spectra display a marked change of slope with a hard component starting at about 1.8 GeV/c, in contrast to central-collision data. The data are discussed in comparison to p+p and α+α data from the ISR.     

Charge and mass distribution of products from the nuclear interaction between copper and 1 GeV 12C

The nuclear interaction between natural copper and 1 GeV ¹²C has been investigated with radiochemical methods. Charge and mass distributions have been derived. The form of the mass yield curve is determined by the total kinetic energy in the system.     

Electrochemical behaviour of graphite cathodes in the presence of tetraalkylammonium cations

A graphite cathode in N,N-dimethylformamide with tetraalkylammonium salts as supporting electrolyte was found to be able to accept reversibly a rather large charge in a way somewhat akin to the formation of anion radicals and ion pairs of polycondensed aromatic hydrocarbons. The charged graphite has certain similarities with an amalgam, it can thus be used as an insoluble chemical reducing agent. The charging of the graphite depends on the size of the cation, in the presence of very large cations the cathode disintegrates. The nature of the charge is discussed on the basis of i-E curves and coulometric results.     

Frequency-dependent damping in structural vibration analysis by use of complex series expansion of transfer functions and numerical Fourier transformation

The response of damped linear finite systems (discrete and continuous) to harmonic, stationary random, and transient excitations is studied. The assumed damping may be light or heavy, viscous and/or hysteretic (the latter being frequency-independent or frequency-dependent), and proportionally or non-proportionally distributed over the structure. Closed-form analytic transfer functions are derived for beam systems. In order to rationalize subsequent numerical calculations, the transfer functions are approximated by using truncated series. Complex eigenfrequencies of the structure and complex residues of the actual transfer function are used. Special interest is paid to the mathematical modelling of experimentally measured damping. Causality requirements are considered. Numerical examples are given. An efficient method (by which aliasing is eliminated) for numerical Fourier transformation has been developed and applied.     

3.508 μ-HeXe-laser line absorption by CH3COOCH3, CH3, and NO2 and infrared emission at 6.89 μ by CH3COOCH3 and CH3 at elevated temperatures

Shock-tube HeXe-laser absorption data at ω_L=2850.633 cm^-1 for CH₃COOCH₃ at 757≤T, °K≤1344, NO₂at 412≤T, °K≤1859, andCH₃at 1283≤T, °K≤1562 are presented. Approximate models are used for the effective spectral absorption coefficient of vibration-rotation lines for analytical representations of the results around atmospheric pressures. For CH₃COOCH₃, an equivalent Voigt-profile for an isolated line was adopted in order to account for a dependence on total pressure of the laser absorption coefficient. Shock-tube emission data at λ=6.890 μ(Δλ=0.197μ) forCH₃COOCH₃at 814≤T, °K≤1651 and for CH₃at 1377≤T, °K≤1562 in the v₄-fundamental of the H-bond bending mode of the CH₃-group are well described at atmospheric pressures by approximations of just-overlapping-line models for polyatomic molecules. The adopted models are useful for concentration-time history measurements of methyl acetate, nitrogen dioxide, and methyl radicals behind shock waves.     

Delayed neutron emission probabilities of gallium,bromine, rubidium,indium, antimony,iodine, and cesium precursors

The delayed neutron emission probability(P _n) has been measured for^79-83Ga,^87-89Br,^92-96Rb^127-132In^134,135Sb^137-139I and^{141 -145}Cs, by means of sources produced at the OSIRIS isotope separator at Studsvik. The half-life determinations of^{127, 129, 132}In have been improved.     

Target fragmentation in proton-nucleus and16O-nucleus reactions at 60 and 200 GeV/nucleon

Target remnants withZ<3 from proton-nucleus and¹⁶O-nucleus reactions at 60 and 200 GeV/nucleon were measured in the angular range from 30° to 160° (?1.7<η<1.3) employing the Plastic Ball detector. The excitation energy of the target spectator matter in central oxygen-induced collisions is found to be high enough to allow for complete disintegration of the target nucleus into fragments withZ<3. The average longitudinal momentum transfer per proton to the target in central collisions is considerably higher in the case of¹⁶O-induced reactions (≈300 MeV/c) than in proton-induced reactions (≈130 MeV/c). The baryon rapidity distributions are roughly in agreement with one-fluid hydrodynamical calculations at 60 GeV/nucleon¹⁶O+Au but are in disagreement at 200 GeV/nucleon, indicating the higher degree of transparency at the higher bombarding energy. Both, the transverse momenta of target spectators and the entropy produced in the target fragmentation region are compared to those attained in head-on collisions of two heavy nuclei at Bevalac energies. They are found to be comparable or do even exceed the values for the participant matter at beam energies of about 1–2 GeV/nucleon.     

Enhancement of positronium formation in some nonpolar liquids caused by scavenging of the highly mobile positive holes

Positronium yields as a function of pyridine concentration were studied in nine nonpolar solvents. Strong enhancements in the Ps yields on addition of low concentrations (< 0.3 M) of the positive hole scavenger pyridine were found in those liquids where the hole moves rapidly (i.e. partly delocalized), but not in those where the hole moves slowly. Pyridine acts also as a very weak Ps inhibitor in all systems investigated if its concentration exceeds a certain limit (≈ 0.3 M). The results can be well interpreted within the framework of the spur reaction model of Ps formation.     

ESR single-crystal study of radical and radical-pair formation in some γ-irradiated vinyl monomers

Single crystals of methyl methacrylate (MMA), methyl acrylate (MA), and acrolein (A) have been prepared by a low-temperature technique. After irradiation with γ-rays at 77°K the paramagnetic species were identified by ESR spectroscopy. MMA gave a seven-line single spectrum from radicals formed by hydrogen addition. The hyperfine coupling constants are slightly anisotropic with a mean value of 22 G. Radical pairs were observed as ΔM_s = 1 and ΔM_s = 2 transitions; the hyperfine coupling was 11 G. From the strongly anisotropic dipolar interaction, upper limits for the distances between the pair components were calculated to be 5.45 Å and 6.3 Å. MA gave a five-line main spectrum with the same hyperfine coupling values and two radical pairs, one with a distance 5.9 Å between the components. In a there was also a strongly anisotropic interaction. The hyperfine coupling of the ΔM_s = 2 transition was 9.8 G. The number of radical pairs compared to the total number of radicals increases only slightly with the radiation dose. This makes it likely that pair formation occurs in the spurs and blobs formed by the γ-radiation. At an increased temperature the radical pairs disappeared; the spectrum of MMA changed to that characteristic of propagating polymer radicals.