Multiplier for delta-modulated signals

A new method for multiplying delta-modulated signals by a constant is suggeated. The rate multiplier is employed here for this multiplication.     

The new external ion beam analysis setup at the Demokritos Tandem accelerator and first applications in cultural heritage

At the 5.5 MV Tandem VdG accelerator of the Institute of Nuclear Physics of N.C.S.R. “Demokritos”, Athens, Greece, an external ion-beam set-up has been recently developed and installed. The aim of this development was to integrate the analytical capabilities of the PIXE, RBS and PIGE ion beam techniques in one experimental set-up, so that to attain a complete elemental and near surface structural characterization of samples in an almost non-destructive way and without any limitation concerning their size or conductive state. A careful 3D mechanical drawing optimized the set-up experimental parameters achieving probe dimensions at the millimeter range (1 mm²) and fulfilling the special requirements imposed for optimum performance of the aforementioned techniques, including the possibility to use heavier, than protons, ion beams. For the digital pulse processing of the X-ray, γ-ray and charged particle detector signals, novel hardware and software tools were developed based on a custom FPGA configuration.The first applications were focused in the quality control of materials that have been intentionally contaminated with a particular tracer-element (“tagged” materials). The tagged materials which were developed and tested are technologically authentic replicas of ancient attic ceramics with black glazed decoration. Analytical diagnostic studies were carried out for a few representative paintings of contemporary Greek painters in order to identify and document materials/pigments and techniques and eventually to prevent trade of fakes. Finally, ancient glass beads were also examined with respect to the sodium concentration and its in-depth homogeneity.     

Oxidation resistance of Y-implanted steel using accelerator based techniques

The thermal oxidation behavior in air of Y-implanted (fluence 2 × 10¹⁷ ions/cm²) and non-implanted stainless steel AISI-321 samples was investigated using the ¹⁶O(d,p)¹⁷O nuclear reaction and Rutherford backscattering spectrometry (RBS). The oxidation temperature was 650 and 900 °C and the duration of the thermal treatment 48 hours. The influence of the implantation energy (40, 55 and 80 keV) on the oxidation behavior of stainless steel was also studied. An improvement of the oxidation resistance of the Y-implanted samples with increasing implantation energy was observed. Additional secondary ion mass spectroscopy (SIMS) measurements of the samples implanted by 40 keV Y-ions also indicated a slight chromium depletion of their near-surface layers. Mechanisms attempting to explain the experimental results are proposed.     

Determination of differential cross-sections for the natK(p, p0) and 39K(p, α0) reactions in the backscattering geometry

In the present work, new, differential cross-section values are presented for the ^natK(p, p₀) reaction in the energy range E_lab = 3000–5000 keV (with an energy step of 25 keV) and for detector angles between 140° and 170° (with an angular step of 10°). A qualitative discussion of the observed cross-section variations through the influence of strong, closely spaced resonances in the p + ³⁹K system is also presented. Information has also been extracted concerning the ³⁹K(p,α₀) reaction for E_lab = 4000–5000 keV in the same angular range. As a result, more than ～500 data points will soon be available to the scientific community through IBANDL (Ion Beam Analysis Nuclear Data Library – http://www-nds.iaea.org/ibandl/) and could thus be incorporated in widely used IBA algorithms (e.g. SIMNRA, WINDF, etc.) for potassium depth profiling at relatively high proton beam energies.     

Differential cross section measurements of the S(d,p)S reaction for nuclear reaction analysis purposes

Differential cross sections of the ³²S(d,p_{0,1,2,3,4-6,7}) reactions were determined for deuteron energies E_lab = 1975-2600 keV (in steps of 25 keV) and for detector angles between 140-170° in steps of 10°. A comparison of the experimental data with the existing ones and possible applications to nuclear reaction analysis (NRA) studies are discussed.     

Differential cross sections for the B(p,αo)Be and B(p,p0)B reactions, suitable for ion beam analysis

Boron depth profiling presents strong analytical challenges for all Ion Beam Analysis (IBA) techniques. In the past, both the ¹¹B(p,α_o)⁸Be (NRA) and the ¹¹B(p,p₀)¹¹B (EBS) reactions have been proposed and they seem to be quite suitable for analytical purposes. Nonetheless, both reactions have not been adequately studied in literature (as far as data suitable for material analysis in the backscattering geometry are concerned). Moreover, the existing datasets are relatively discrepant. In an attempt to clarify the situation, both reactions were studied in the present work between 135° and 160°, in steps of 5°, for the proton beam energy range between 2.2 and 4.2 MeV, in steps of 50 keV. An attempt to explain the occurring results in the framework of the resonance mechanism is also presented, along with a comparison with previously published data.     

A new recoil distance technique using low energy coulomb excitation in inverse kinematics

We report on the first experiment combining the Recoil Distance Doppler Shift technique and multistep Coulomb excitation in inverse kinematics at beam energies of 3-10 A MeV. The setup involves a standard plunger device equipped with a degrader foil instead of the normally used stopper foil. An array of particle detectors is positioned at forward angles to detect target-like recoil nuclei which are used as a trigger to discriminate against excitations in the degrader foil. The method has been successfully applied to measure lifetimes in ¹²⁸Xe and is suited to be a useful tool for experiments with radioactive ion beams.     

Correlator based on delta-sigma modulation

The delta-sigma modulation (d.s.m.) technique has been employed for the realisation of a simple correlator which can be used for limited-bandwidth signals.