A method for the simultaneous determination of 21 elements in high purity silicon was developed by activation analysis. Extraction,
ion exchange, distillation and precipitation techniques were used combined with NaI(Tl) and Ge(Li) γ-spectrometry. Attention
was paid to the separation time, sensitivity and selectivity of the method.
32P was separated from the irradiated silicon matrix as ammonium phosphomolybdate and the activity was measured with a GM tube
or on a plastic scintillator. The second-order interference was taken into consideration.
Authors:G. Wauters, C. Vandecasteele, and J. Hoste
Lead is determined in environmental samples and in rocks using the206,207,208Pb(p,xn)206Bi reaction. Bismuth is separated by anion exchange or by extraction with antimony diethyldithiocarbamate. Sources of errors such as volatilization of the matrix due to heating during the irradiation, variations of the abundance of the lead isotopes and the standardization were studied in detail. For concentrations between 11 mg/g and 3.7 g/g the relative standard deviation ranges from 2.6 to 5.4%. The detection limit is 10 ng/g.
Different methods for the determination of thermal-to-epithermal neutron flux ratio are reviewed and nuclear data for commonly
used monitor materials and for Zr isotopes are tabulated. It is shown that the use of the94Zr−96Zr isotope pair gives significant improvement in precision while measuring Φth/Φe ratios in the 20<Φth/Φe<200 range. When the single comparator method is applied, the use of the94Zr isotope is suggested as a comparator with the94Zr−96Zr isotope pair for simultaneous flux ratio determination. Theoretical calculations show that the Zr comparator-flux ratio
monitor gives better precision and accuracy than does Ru for two-thirds of the isotopes used for analysis in well thermalized
(Φth/Φe>100) channels. The Io/σth-values for the mentioned Zr isotopes have been experimentally determined and compared with previously published data.
Two methods are described to determine indium and managenese in high-purity tin. In the first method indium and manganese
are separated from the tin and antimony matrix activities on Dowex 1X8 anion exchanger. Tin and antimony are adsorbed in 10M HF while indium and manganese are eluted. In the second method the incident γ-ray intensity due to the tin matrix is reduced
by placing a lead absorber between the sample and the detector. The reproducibility and the sensitivity of both methods are
of the order of 10 ppb for manganese and of 1 ppb for indium for 1 g samples and a neutron flux of 1011 n·cm−2·sec−1.
Authors:G. Wauters, C. Vandecasteele, and J. Hostè
The temperature in powdered rock and environmental samples irradiated with 23 MeV protons was measured. Under helium (3–9·105 Pa) the obtained temperature is considerably lower than under vacuum. Irradiation under helium at a sufficiently low beam intensity allows to avoid systematic errors that may occur in charged particle activation analysis due to volatilization of matrix components.
The accuracy of the live-time circuit of a 400-channel analyzer was studied in detail, and was found to be unsatisfactory
even for long-lived radionuclides. It was found that automatic live-time correction with the multi-channel analyzer gave rise
to increasing positive errors with increasing count rate; this overall positive error was composed of a positive error due
to the slowness of the electronic circuitry, and a smaller negative error due to the finite pulse-width. Adequate correction
could be performed by feeding the information from the dead-time output of the multi-channel analyzer to an external live-time
circuit with variable oscillator frequency and pulse-width. Four methods for dead-time correction were compared experimentally
in the case of short-lived radionuclides (T as low as 7 sec): the method of Bartošek et al., the method of Schonfeld, the
use of a sufficiently short counting time as compared to the half-life, and the live-time mode of counting without additional
correction. These four methods were applied to the determination of oxygen and silicon in rocks by 14 MeV neutron activation
analysis. Results are given for USGS standard rock G-2.
The single comparator method has been extended to a triple comparator method, using60Co,114mIn and198Au. In this technique, thek-ratios of the elements to be analyzed, now determined against the three comparators, are corrected for each new ratio of
thermal to epithermal reactor neutron flux. These flux ratios are calculated from the absolute activities of the three comparators.
The thermal neutron activation cross-section and the resonance integral for the reaction113In(n,γ)114mIn have been determined.
was experimentally determined for the reactions42Ca(n, p)42K,43Ca(n, p)43K and44Ca(n, p)44K. Calcium carbonate samples and fast neutron flux monitors were irradiated with and without cadmium shielding in the Thetis
reactor (Institute for Nuclear Sciences, Rijksuniversiteit, Gent). The potassium activities induced in the calcium carbonate
samples were separated and purified by tetraphenylborate precipitation, after which they were measured with a Ge(Li)-detector
of calibrated detection efficiency. On the basis of
A fast (10 min), non-destructive simultaneous determination of silicon and phosphorus in cast iron and steel by 14 MeV neutron
activation was developed. The 1.78 MeV28Al activity (T=2.24 min) induced by the reaction28Si(n, p)28Al is counted on a NaI(Tl) detector. Two measurements are made to correct for the 1.81 MeV56Mn activity (T=2.58 hr) from the iron matrix. However,28Al is also produced via31P(n, α)28Al. By (n, 2n) reaction, phosphorus yields also30P (T=2.6 min), the 0.511 MeV annihilation radiation of which is counted by two opposite NaI(Tl) detectors in coincidence.
Again, two successive coincidence measurements are carried out in order to take into account the53Fe activity (β+; T=8.9 min) from54Fe(n, 2n)53Fe. The28Al measurement is appropriately corrected via the computed phosphorus content. An oxygen flux monitor was used to normalize
to the same flux. Nuclear interferences have been examined. Special attention has been paid to the presence of copper. The
standard deviation for phosphorus being as high as ca. 0.09% P for a single determination, this technique can only be practical
as an independent phosphorus analysis for high phosphorus cast irons. The precision on the28Al measurement is 5% relative for 0.2% Si and 2.5% above 1% Si.