The structure of events triggered by direct photons in π− p, π+ p andpp collisions at 280 GeV/c

The structure of events associated with the production of direct photons in π^? p, π⁺ p andpp reactions of 280 GeV/c has been studied using data from the WA 70 experiment at the CERN SPS. Results are presented on the distributions of the fractional momenta of the colliding partons and on the fragmentation of the recoil jet and a comparison is made with predictions using the structure functions of Duke and Owens in the Lund Monte Carlo with string fragmentation.     

Influence of salt and rinsing protocol on the structure of PAH/PSS polyelectrolyte multilayers

A quartz crystal microbalance (QCM) and dual polarization interferometry (DPI) have been utilized to study how the structure of poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) multilayers is affected by the rinsing method (i.e., the termination of polyelectrolyte adsorption). The effect of the type of counterions used in the deposition solution was also investigated, and the polyelectrolyte multilayers were formed in a 0.5 M electrolyte solution (NaCl and KBr). From the measurements, it was observed that thicker layers were obtained when using KBr in the deposition solution than when using NaCl. Three different rinsing protocols have been studied: (i) the same electrolyte solution as used during multilayer formation, (ii) pure water, and (iii) first a salt solution (0.5 M) and then pure water. When the multilayer with PAH as the outermost layer was exposed to pure water, an interesting phenomenon was discovered: a large change in the energy dissipation was measured with the QCM. This could be attributed to the swelling of the layer, and from both QCM and DPI it is obvious that only the outermost PAH layer swells (to a thickness of 25-30 nm) because of a decrease in ionic strength and hence an increase in intra- and interchain repulsion, whereas the underlying layers retain a very rigid and compact structure with a low water content. Interestingly, the outermost PAH layer seems to obtain very similar thicknesses in water independent of the electrolyte used for the multilayer buildup. Another interesting aspect was that the measured thickness with the DPI evaluated by a single-layer model did not correlate with the estimated thickness from the model calculations performed on the QCM-D data. Thus, we applied a two-layer model to evaluate the DPI data and the results were in excellent agreement with the QCM-D results. To our knowledge, this evaluation of DPI data has not been done previously.     

Micromegas prototypes with thermo-bond film separators

In this paper we report the results of Micromegas prototypes constructed by attaching micromesh to an anode using thermo-bond films. The excellent metal attaching ability and good dielectical property of this kind of film make it a promising material to be used as avalanche gap spacers. Several prototypes are successfully made. The electron transmission properties are first studied and then the gas gain is measured in argon-isobutane mixtures. The maximum gain of more than 10⁴ is easily obtained. The energy resolutions for ⁵⁵Fe 5.9 keV K_α ray can be better than 20% over one magnitude in gain for different operational gas mixtures and the best energy resolution of 13.7% (FWHM) can be achieved with the gas mixture of 94% argon concentration. The preliminary test results of the prototypes with sensitive area of 45 mm×45 mm without internal support show good uniformity across the sensitive area.     

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.     

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.     

Studies of weak interaction effects by laser spectroscopy of short-lived atoms

Laser-induced nuclear orientation has been used to make sub-Doppler-resolution measurements of a nuclear isomer^85mRb that has a lifetime of only a microsecond. The technique succeeds because the sampled atoms remove themselves before equilibrating. This paper describes two cases in which pre-equilibrium removal of atoms can prevent thermal equilibrium from obscuring information about the weak interaction that is present in the velocity profile of atoms as they recoil following beta decay. It should be possible to measure electron-antineutrino angular correlations in the beta decay of⁸⁵Kr, and to look for beta decay of tritium into an atomic bound state of³He-a fundamental effect predicted by weak interaction theory but never observed.     

An optoelectronic recirculating sorter based on CMOS/vertical cavity surface emitting laser smart pixel arrays; architecture and system demonstration

The architecture of an optoelectronic recirculating sorter based on the hybrid integration of CMOS logic circuitry, silicon detector/receivers and vertical cavity surface emitting lasers is presented along with the demonstration of the system.