Stjepko Fazinić

IBIC investigations on CVD diamond

A 3 MeV proton microbeam has been used for the first time both to investigate the transport properties and to probe the electrical field in a CVD diamond sample of detector grade. Qualitative results concerning the spatial distribution of charge collection efficiency and, consequently, of the collection length are obtained. Collection length seems to be of the order of several tens of microns only in small regions of the same dimensions, characterized probably by a good crystalline behaviour. A strong polarization due to the creation of a local internal electric field and ascribed to the space-charge accumulated in the grain boundaries, makes the measurements very difficult and reduces the statistical validity of the data. However, imaging of physical quantities like collection length is concluded to be a viable technique and it will constitute a useful and powerful method of investigating homogeneity of nuclear detectors and of other similar devices.

The 2000 IAEA intercomparison of PIXE spectrum analysis software

Seven programs for analysis of PIXE spectra were compared using the 2000 IAEA test spectra, i.e. Geopixe, Gupix, Pixan, Pixeklm, Sapix, Winaxil and Witshex. A systematic statistical study of the analysis results was performed based on z-scores. The results indicate that most of the programs perform reasonably well with respect to peak areas. Except for a very rare exception, the statistical analysis shows that the participants generally reported smaller uncertainties than would have been expected from the reference uncertainty values. The results show that all the participants reported a number of statistically significant “false hits” and “misses” in their reports. All this indicates that programs in general still leave room for further improvements.

Data acquisition and scan control system for nuclear microprobe and other multiparameter experiments

Abstract A multipurpose data acquisition and beam control system was developed for use on a personal computer (PC) in an MS Windows graphical environment. Data acquisition is performed via a FAST MPA/PC adapter card and MPA/LBB large bus-box by a host computer. Beam and sample positioning are controlled from another computer connected to the host. Applications in the nuclear microprobe and experimental nuclear physics are presented.

Investigation on the electric field profile in CdTe by ion beam induced current

Abstract The charge collection efficiency profile along the thickness of a CdTe detector was measured for first time by using a proton microbeam and a polished cross-section of the devices. Different samples were investigated and tests were carried out along different lines from cathode to anode, with different biases and polarities, and with different shaping times. The effects of all these parameters are evident in the experimental curves. By fitting these curves, the behaviour of the drift length for electrons and holes is obtained, if a constant ratio between them is assumed. If the mobilities and trapping times are uniform, the electric field profile is obtained. The profile has a minimum at the anode and a maximum towards the cathode, at least for large bias voltage.

Trace element characterization of coal fly ash particles

Abstract XRF, PIXE, RBS and STIM were used for a study of trace element distributions in Greek lignites and their ashes. Samples of fly ash collected from electrostatic precipitators have been separated into seven fractional sizes ranging from 300 μm to less than 25 μm. Trace element concentrations show variation as function of grain size. In addition, the results of analyses of 50 individual fly ash particles are presented.

K-shell ionization of V, Cr, Mn, Fe, Co, Ni and Cu by 5-12 MeV carbon ions

Abstract The K-shell X-rays of V, Cr, Mn, Fe, Co, Ni and Cu induced by 12C ions were detected in the projectile energy range 5–12 MeV. From these measurements, experimental K-shell X-ray production cross sections; Kα, Kβ X-ray energy shifts and the K α K β intensity ratios are extracted and presented. Our results are compared with the experimental data obtained previously and with the predictions of the perturbed stationary-state approximation with energy loss, Coulomb, and relativistic corrections (ECPSSR theory). The role of electron transfer to the projectile have been discussed.

Quantitative PIXE analysis of single fly ash particles by a proton microbeam

Abstract Methods of quantitative PIXE analysis of individual particles in the diameter range between 5 and 10 μm are presented. Two different approaches to the analysis are considered. In the first case, an analysis is performed with a proton mubeam centered at the middle of the particle. In the second case, the beam is scanned over the whole particle. Absorption correction methods were developed for both cases. Advantages and drawbacks are discussed on the basis of analysis of individual fly ash particles.

THE 1997 IAEA INTERCOMPARISON OF COMMERCIALLY AVAILABLE PC-BASED SOFTWARE FOR ALPHA-PARTICLE SPECTROMETRY

Abstract Four commercially available, PC-based analysis programs for alpha-particle spectrometry were compared using the 1997 IAEA test spectra, i.e. AlphaVision 1.20 (EG&G Ortec, USA), Alps 4.21 (Westmeier GmbH, Germany), Winner Alpha 4.0f5 (Eurisys Mesures, France) and Genie-2000 (Canberra Industries Inc., USA). A systematic statistical study of the analysis results was performed based on z -scores. The results indicate that the four programs leave room for substantial improvement.

USE OF STIM IN THE PROTON MICROPROBE ANALYSIS OF SINGLE PARTICLES

Abstract Scanning proton microprobe data are usually presented as plots of elemental intensity maps. However, these maps do not present actual concentration distributions, due to variations in energy loss and X-ray absorption, caused by local changes of the sample areal density and topology. Scanning transmission ion microscopy (STIM) is the method that can provide additional information of importance for evaluation of these effects. The use of particle shape and areal density distribution, determined by STIM, in the case of single particle analysis is presented in this paper.

Quality control of PIXE and PIGE nuclear analytical techniques in geological and environmental applications

Abstract Several powder standard reference materials (SRM) used mainly in geological and environmental applications have been tested for reliability on miligram scale. Specific experimental conditions such as beam energy and diameter, as well as the matrix composition of the analysed samples, determine a lower limit on the necessary mass for which the SRM must be homogeneous. These mass limits have been determined for specific elements and are compared to the minimal mass required for analysis as specified by the certifying body. Since the accuracy of PIGE analysis is often hindered by the presence of interfering nuclear reactions, this narrows down the useful number of elements for which the SRM is certified.