[en] The πK scattering lengths are obtained from a dispersion relation analysis of recent phenomenological πK phase-shifts, and the results are compared with the predictions of current algebra. (author)

[en] A position-sensitive γ-camera is being currently designed at IASA. This camera will be used experimentally (development mode) in order to obtain an integrated knowledge of its function and perhaps to improve its performance in parallel with an existing one, which has shown a very good performance in phantom, small animal, SPECT technique and is currently being tested for clinical applications. The new system is a combination of a PSPMT (Hamamatsu, R2486-05) and a PMT for simultaneous or independent acquisition of energy and position information, respectively. The resistive chain technique resulting in two signals at each (X,Y) direction will perform the readout of the PSPMT's anode signals; the system is based on PCI electronics. Status of the system's development and the ongoing progress is presented

[en] A new image reconstruction technique based on the usage of an Artificial Neural Network (ANN) is presented. The most crucial factor in designing such a reconstruction system is the network architecture and the number of the input projections needed to reconstruct the image. Although the training phase requires a large amount of input samples and a considerable CPU time, the trained network is characterized by simplicity and quick response. The performance of this ANN is tested using several image patterns. It is intended to be used together with a phantom rotating table and the γ-camera of IASA for SPECT image reconstruction

[en] A study of energy spectra (Smith-Purcell power, energy peaks, and shape of the spectra) is performed using a Monte Carlo simulation method. This was done in order to examine the dependence from the experimental parameters. The setup for an experiment looking for Smith-Purcell radiation in the IR and FIR region is also presented. Experiment is taking place at the beginning of year 2000 in Bucharest (Romania) at the National Institute for Laser, Plasma and Radiation Physics, at the betatron facilities of the Electron Accelerator Laboratory with an electron beam up to 30 MeV. This experiment will be continued later on in Athens (Greece), at the Institute of Accelerating Systems and Applications (IASA) with a linac delivering up to 10 MeV CW electron beam

[en] In this paper, we present the 'point matching method' (PMM) adapted for the calculation of Smith-Purcell (SP) radiation parameters in H-polarization, generated by relativistic electron beams (REB) passing close to a triangular metal grating. A truncated expression H^d_y,n(N;β,ω) was used in order to find the coefficients H^d_y,n(β,ω) in the infinite Rayleigh expansion of the diffracted field of a moving electron. A linear system of 2N+1 equations was solved, increasing the number N of harmonics until convergence solutions were achieved. When N→∞ then lim_N→∞H^d_y,n(N;β,ω)=H^d_y,n(β,ω) and the diffracted field can be calculated. SP radiation factors were calculated using the modified PMM for electron energies in 1-30 MeV domain and metal gratings with period length in 1-10 mm range

[en] A phenomenological method is proposed to select possible Quark matter forming events in ultra-relativistic nucleus-nucleus interactions. We compare the released photonic and hadronic energies from a Quark matter forming event and from a normal Hadronic event and derive a relation, which may be used in an event-by-event analysis to differentiate the two phases. We determine thus two regions of QCD deconfinement. We also discuss the hadronic, photonic energy and multiplicity contents and the < P_T> of several exotic cosmic ray events at ultra high energies. On the basis of the phenomenological model, we suggest that the 'Centauro' type are Quark matter events near the projectile fragmentation region with very large baryochemical potential, μ_b. The 'Anti-Centauro' type events are created by vacuum excitation in the central region with near zero μ_b. (orig.)

[en] Studies have been performed in order to optimize the collimator and the crystal of a γ-camera based on a position sensitive photomultiplier with respect its efficiency, its spatial resolution and its cost. Several parallel hole collimators of different thicknesses have been tested and compared to each other. The homogeneous crystals' performance has also been compared to that of a pixelized CsI(Tl) crystal. It is shown that though the spatial resolution of the homogeneous crystals is not as good as that of the pixelized one it is still reasonable and it could probably be improved by the choice of a better position reconstruction algorithm

No abstract available

[en] Direct photon and neutral-pion production have been measured in pp collisions at the CERN ISR for 30 < √s < 63 GeV and transverse momenta up to 12 GeV/c. The direct photon signal relative to neutral-pion production increases with psub(T) and shows little √s-dependence. Results are reported from a variety of running conditions, and details are given on the method of analysis and on the evaluation of systematic errors for the inclusive cross-section of single-photon and neutral-pion production. (orig.)

[en] Inclusive π⁰ production has been measured at the CERN Intersecting Storage Rings in αα and αp collisions near 90⁰, for psub(T) between 2 and 5 GeV/c. The differential cross sections show a slower exponential fall-off with psub(T) than has been observed in pp collisions at the corresponding nucleon-nucleon centre-of-mass energies at large psub(T). The ratio of the π⁰ production cross sections for αα collisions to those for pp collisions is observed to be larger than 16. (orig.)