[en] Experimental values of proton-induced L-shell x-ray production and ionization cross sections are tabulated. Data for individual L x-ray transitions and L-subshell ionization are presented separately according to incident proton energy and target atomic number in two tables. Experimental details and techniques employed by different authors are summarized as well. This work covers experimental data published in the period between 1982 and December 1992. It comprises more than 6000 newly compiled L-shell cross-section data and it is a continuation of a similar tabulation produced by Sokhi and Crumpton. 58 refs., 3 figs., 3 tabs

[en] Thirty-eight core sediment samples were recently collected from different locations of the Singapore coastal region. The aim of the project was to trace the history of marine pollution in various coastal regions and to determine the impact of industrial activities. Two nuclear analytical techniques were employed in this study: particle induced X-ray emission (PIXE), Rutherford backscattering (RBS) as well as X-ray fluorescence (XRF). Combined together these techniques provide an excellent tool to determine elemental concentrations of more than 30 elements with detection limits as low as few ppm. Our results show that elemental concentrations in most of the regions do not show a significant variation with depth. However, in regions where industrial and shipping activities are high, for example the Port of Singapore area and the northern part of Johore Straits, the concentrations of metals like Cr, Ni, Cu, Zn, Sn and Pb were found to have an obvious decreasing trend with the depth. In these cores, concentrations in the top 10-15 cm were sometimes ten times higher than the corresponding base line concentrations. Elemental depth profiles of Ni, Cu, Zn, As, Sn and Pb and their mean concentrations in various regions are reported and discussed

[en] The recent report of marketing of radioactive chrysoberyl cat's-eyes in South-East Asian markets has led us to use an indirect method to estimate the threat to health these color-enhanced gemstones may pose if worn close to skin. We determined the impurity content of several cat's-eye chrysoberyls from Indian States of Orissa and Kerala using PIXE, and calculated the radioactivity that would be generated from these impurities and the constitutional elements if a chrysoberyl was irradiated by neutrons in a nuclear reactor for color enhancement. Of all the radioactive nuclides that could be created by neutron irradiation, only four (⁴⁶Sc, ⁵¹Cr, ⁵⁴Mn and ⁵⁹Fe) would not have cooled down within a month after irradiation to the internationally accepted level of specific residual radioactivity of 2 nCi/g. The radioactivity of ⁴⁶Sc, ⁵¹Cr and ⁵⁹Fe would only fall to this safe limit after 15 months and that of ⁵⁴Mn could remain above this limit for several years

[en] Concentrations of aerosols collected in Singapore during the three months long haze period that affected the whole South-East Asian region in 1997 are reported. Aerosol samples were continuously collected by using a fine aerosol sampler (PM2.5) and occasionally with a single orifice cascade impactor (CI) sampler. Our results show that in the fine fraction (<2.5 μm) the concentrations of two well-known biomass burning products, i.e. K and S were generally increased by a factor 2-3 compared to the non-hazy periods. However, a discrepancy was noticed, at least for elements with lower atomic number (Ti and below) between the results obtained by the fine aerosol sampler and the cascade impactor. Careful analysis by means of Nuclear Microscopy, in particular by the Scanning Transmission Ion Microscopy (STIM) technique, revealed that thicknesses of the lower CI stages exceeded thick target limits for 2 MeV protons. Detailed depth profiles of all CI stages were therefore measured using the STIM technique and concentrations corrected for absorption and proton energy loss. After correcting results for the actual sample thickness, concentrations of all major elements (S, Cl, K, Ca) agreed much better with the PM2.5 results. The importance of implementing thick target corrections in analysis of CI samples, especially those collected in the urban environments, is emphasized. Broad beam PIXE analysis approach is certainly not adequate in these cases

[en] Americium-241 source was used to investigate elements whose fluorescent X-ray energies are between about 25 and 40 keV. We did not find any correlation between the amount of the elements present and the time of manufacture except for barium, which can therefore be used to detect modern reproductions. This method of detection is both quick and non-destructive. (author)

[en] Ambient aerosol samples were collected near an industrial area in Singapore during the period of July 91 to January 92. The sampling site was a highway at a height of about 20 m. PIXE analysis of these samples was carried out using 1.8 MeV protons. Thirteen trace elements were observed, ranging from Si to Pb. Among these, Cl and S had the highest concentrations. The former was attributed to the sea-salt particles and the latter could be due to the presence of oil refineries in the vicinity. Pb was found to be below the detection limit of 30 ng m^-3 in most of the samples analysed. This is likely due to the fact that unleaded petrol was used by many cars in Singapore and that the sampling point was quite a distance away from the ground level. The observed variations in concentration for most of the trace elements were well-correlated with traffic intensity and meteorological conditions. Time variation patterns on weekdays and during weekends were also observed. A higher level of pollutants was detected during the period when there were prolonged forest fires in the nearby islands in Indonesia. (orig.)

[en] The relative gamma intensities of the 53 keV, 130 keV, 279 keV and 346.5 keV transitions in the decay of ¹⁹⁷Ptsup(m) are determined, by using a high-resolution HPGe system. The total-conversion coefficients of the 130 keV and 346.5 keV transitions are evaluated from the relative intensities as 29.4(50) and 7.7(4), respectively, in agreement with the theoretical values

[en] An aerosol sampling campaign was initiated more than two years ago in Singapore. The aim was to determine the average elemental concentrations in fine and coarse aerosol fractions as well as to identify major pollution sources and their impact. For that purpose, two air samplers were employed at two different sampling locations; one sampler was a fine particulate aerosol sampler (PM2.5) located at the vicinity of a major industrial area. The other was a stacked filter unit (SFU) sampler designed for collection of fine and coarse fractions (PM2.5 and PM10) and installed in the residential area. Samples were taken typically twice a week and in several occasions daily. During the period of two years more than 700 aerosol samples were collected and analyzed using PIXE and RBS techniques. All samples were analyzed for 18 elements ranging between Na, Mg, Al, etc. up to As and Pb. Large daily and seasonal variations were found for most of the elements. These variations are attributed mainly to meteorological changes, in particular changes in wind speed and direction. On several occasions, short term sampling was performed to identify fingerprints of major pollution sources such as road traffic, refineries, as well as the rain-forest fires in neighboring countries. A summary of our findings is presented and discussed

[en] A convenient way to generate mass attenuation coefficients for data analysis in the various fields of applied X-ray spectroscopy is by means of semi-empirical schemes. Unfortunately, their simplicity often results in a limited range of validity. To highlight this problem we compare the mass attentuation coefficients obtained from some popular schemes with theoretically calculated values and some accurate experimental data. We propose a new scheme which is flexible enough to fit data in a wide photon energy range from 0.1 to 1000keV. A new set of empirical parameters was obtained by fitting this scheme to recently tabulated theoretical and experimental mass attenuation coefficients for atomic numbers 1 to 40. The root mean squares of fit are generally less than 0.3% except for energies below 1 keV where they are higher due to scattered experimental data. A computer code for generating mass attenuation coefficients based on the proposed scheme has been developed. (author)

[en] Presented are new parameters for the calculation of L subshell ionization cross sections for proton impact using a semiempirical expression. A similar paper was published by our group in early 1993 but the fitting parameters were obtained by using only 2295 experimental L shell cross section data. Since then a large number of experimental data have become available and therefore a new fitting has been performed employing more than 5000 data points. All available data were fitted separately for L1, L2 and L3 subshells. For targets with low atomic numbers (14 ≤ Z ≤ 42), only coefficients for L_tot were obtained. Because of the slight Z dependence of the universal function, data were also devised into five sub-groups according to their atomic numbers and fitted separately within each group for L1, L2 and L3 subshells. To extend the energy range of validity of the new fitting function theoretical values were used in the high energy region where experimental data were lacking. Results are compared with ECPSSR predictions and discussed. (author)