J.A. Liendo

Comparison between proton-induced X-ray emission (PIXE) and total reflection X-ray fluorescence (TXRF) spectrometry for the elemental analysis of human amniotic fluid

A comparison between use of proton-induced x-ray emission (PIXE) and total reflection x-ray fluorescence (TXRF) techniques in relation to the elemental analysis of amniotic fluid (AF) was carried out by measuring the concentrations of Cl, K, Ca, Fe, Cu, Zn and Br. For 10 AF samples analyzed, the agreement between PIXE and a TXRF measurements was 100% for K, 60% for Cl and Ca, 80% for Fe and 50% for Cu. For Zn, although there was only a 20% agreement, the measured concentrations ranged between 0.1 and 1 μg/ml with a TXRF standard deviation as high as 0.070 μg/ml. For Br, a factor of 1.8±0.2 was obtained between TXRF and PIXE measurements, suggesting a systematic error between experiments. This work indicates that further investigation is required to determine the experimental conditions, e.g. sample preparation and irradiation, which lead to complete agreement between TXRF and PIXE when a complicated organic sample such as amniotic fluid is analyzed. Copyright

Radon monitoring for health studies in the Caracas subway using SSNTDS

Abstract The additional dose due to environmental radioactivity in the underground transport system of Caracas was determined. Measurements employed the exposure of SSNTD (LR-115) to determine radon concentration and TLD (for gamma dose). The average radon concentration is 30 Bq/m 3 . Calculated effective dose for METRO employed personnel is 1.0 mSv/y and for a typical passenger is 10 μSv/y.

Environmental gamma and radon dosimetry in Venezuela

Abstract Environmental gamma exposure and radon concentration levels measured in Venezuelan regions are presented. A new generation image analyser was used for α particle track counting in CR-39 detectors. Mineral water wells from where water is supplied for massive consumption have an alpha activity around 0.450 Bq L −1 and few of them have concentrations above 50 Bq L −1 . Coastal potable water activity is on the average around 5.3 ± 12% Bq L −1 . Indoor radon national average is 36 ± 5% Bq m −3 ; in two of the 36 monitored sites, the measured average is above 400 ± 5% Bq m −3 . In air gamma dose values are between 100 and 144 nGy h −1 . In soil, 137 Cs concentration is around 0.5 and 10 Bq kg −1 at the depth of down to 20 cm. Building materials were included in this study. 7 Be and 137 Cs were measured in low concentration in tropical plants on Tepuy-s (sacred mountains in the Amazonas State). Geological active faults were identified by radon concentration measurements using LR-115.

Target preparation and characterization for multielemental analysis of liquid samples by use of accelerators

Abstract Elastic scattering at forward angles is tested as a useful alternative method to characterize liquid samples of scientific and/or technological interest. Solid residues of such samples deposited on light backings have been bombarded with 16 MeV 7 Li and 24 MeV 16 O beams in order to determine the experimental configuration giving the best elemental mass separation. The elastically scattered ions were detected at 16°, 20° and 28° with surface barrier detectors. The ratios between the mass separation and the line width obtained in the spectral region between carbon and oxygen varied between 2 and 13. This method is particularly useful for an accurate elemental characterization below sodium which is beyond the scope of standard techniques such as PIXE and TXRF provided the ion beam type, its kinetic energy and the target thickness are considered simultaneously.

Preliminary results on the use of Rutherford forward scattering for the elemental analysis of liquid organic samples

Abstract A new method proposed for the elemental analysis of liquid organic samples has been used in this pilot investigation to determine the concentration of several non-volatile light elements contained in human amniotic fluid (AF) from a single measurement. The technique is based on Rutherford forward scattering (RFS) at 28° of a 16 MeV 7 Li beam from vacuum dried AF samples deposited on a formvar support. The risk of contamination of the AF sample due to its manipulation is minimum since it is not required to treat the sample chemically. Statistically significant yields were obtained for beam currents of 5 nA and irradiation periods of 30 min approximately. An energy calibration with the spectrum obtained from the irradiation of an AF target was carried out to take into account any effect due to the AF organic matrix. AF spectra were quantified by a chi square fitting of Gaussian curves to element signals. According to this study, the RFS method may be considered as a potential method for light trace element analysis of non-volatile fractions where standard techniques such as PIXE/PIGE and TXRF are difficult to apply.

Cross Section Measurements for the Forward Elastic Scattering of 13 MeV 6,7 Li and 24 MeV 16 O from 9 Be, 12 C, 16 O and 28 Si

Absolute elastic cross sections have been measured at 12.45°, 16.45°, 20.45° and 28.0° for targets of 9Be, 12C, 16O, 28Si and 197Au being bombarded by beams of 13 MeV 6,7Li and 24 MeV 16O. The reliability of a method previously proposed for low mass multielemental analysis [1,2] depends to some extent on the precision and accuracy of the cross sections reported here. The 16O-beam reactions, except the 16O + 9Be reaction, are found to be consistent with the Rutherford predictions. This allows us to obtain target thickness independent cross sections with uncertainties of approximately 7% for the reactions initiated with 6,7Li beams. Most of these cross sections are found to be non-Rutherford. Comparisons made with previous investigations give strong support to the cross section values obtained in this work.

Increasing reliability in gamma and X-ray spectral data analysis: least moduli approach

Abstract A method for increasing reliability of parameter estimations for X- and gamma-ray spectral data acquired by semiconductor detectors and multichannel analyzers has been developed. We describe the advantages of using the method of least moduli over the method of least squares when analyzing peaks with high peak/background ratios. The influence of different distortion factors was explored along with the limitations on applying the new method.

APPROXIMATION OF SPECTRUM ALPHA PEAKS BY ROBUST ESTIMATION

Abstract A fitting method based on the robust approach M-Hubers estimate has been developed to analyze alpha spectra. It is shown that the approximation depends on the method of estimation for a selected model. The advantage of this technique is demonstrated by processing experimental alpha spectra using a special purpose computer program.

Investigation of lithium forward scattering for the analysis of carbon and oxygen in human amniotic fluid

Lithium forward elastic scattering is investigated as an additional method for Z<11 multielemental analysis in human amniotic fluid (AF). Concentrations of C and O are obtained from the analysis of an AF sample that is diluted with distilled water, deposited on a formvar backing and dried naturally. Solid residues of this diluted sample are bombarded with 13 MeV 6,7Li beams and the elastically scattered beam is detected at 16.45o, 20.45o and 28.0o simultaneously. The quality of elastic spectra improves with sample dilution. The content of C and O in the backing is subtracted. Carbon and oxygen concentrations of the non-diluted AF sample are determined by assuming that elemental concentration varies linearly with dilution.

Status and Perspectives of a Forward Scattering Project for the Multielemental Analysis of Liquids

A project based on low mass multielemental analysis of liquid samples by using forward elastic scattering is under progress. Elastic cross section measurements for the reactions 13 MeV 6,7Li +A and 24 MeV 16O +A, A being any nucleus lighter than Na, are necessary due to the existence of non‐elastic processes. The non‐Rutherford character of some of the reactions quoted above has been established from experiments carried out at 12.45°, 16.45°, 20.45° and 28.0° where A = Be, C, O and Si. The accuracy and precision of the measured cross sections have been tested. In the future, accurate cross section determinations will be required for lighter target elements such as B, Li and H. The dilution of a liquid sample improves the spectrum resolution. Efforts are currently concentrated on determining if the relative yields corresponding to various elements present in a given sample remain constant as dilution changes.