The determination of boron, carbon, nitrogen and oxygen in metals and semiconductors by charged particle activation analysis (CPAA) is reviewed. It is shown that CPAA is a sensitive and accurate method suitable for the analysis of reference materials.
Standardization methods in activation analysis with charged particles are studied critically. Several approximate standardization
methods that do not require knowledge of the excitation function are compared with the “numerical integration method” using
excitation function data from the literature. It is shown that these methods yield accurate results if the threshold energy
of the considered reaction is high and if sample and standard have a comparable Z value. A method that gives a rapid estimate
of the maximum possible error is also presented. It is shown that for the “numerical integration method” the accuracy of the
excitation function data has only a small influence on the overall accuracy. The influence of the accuracy of stopping power
data and of possible deviations from Bragg's rule for light element standards is also considered.
The determination of oxygen in lead by3He and4He activation analysis was studied. Both methods were applied to the same material containing 0.9 μg·g−1 of oxygen. The18F formed from oxygen was separated from matrix activities by extraction of Po with N-benzoyl-N-fenylhydroxylamine, followed
by distillation of fluorosilicic acid and precipitation of lead fluorochloride (4He activation) or by distillation followed by precipitation (3He activation). The yield of the separation, which amounted on the average to 68%, was determined via the19F(n,4He)16N reaction. The coefficients of variation were 21 and 45% for4He and3He activation analysis, respectively, thus indicating a less homogeneous distribution of the oxygen. Nuclear interferences
of sodium and fluorine were shown to be negligible.
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.
Fast neutrons are produced by irradiation of a thick beryllium target with deuterons from a cyclotron. The spatial neutron flux distribution was studied. Ge(Li) gamma-ray spectrometry was used to measure the radionuclides produced. Detection limits are tabulated along with the nuclear interferences.
Authors:G. Wauters, C. Vandecasteele and K. Strijckmans
This paper considers the variable isotopic composition of lead as a possible source of systematic errors in proton activation analysis. The importance of this source of error was evaluated for environmental and geological samples. As proton activation analysis is frequently used for the certification of lead, the error was determined for three sediment reference materials. Inductively coupled plasma-mass spectrometry was used for the determination of the isotopic composition of lead. The systematic error amounted for the sediments to approximately 1%.
Authors:K. Strijckmans, N. De Brucker and C. Vandecasteele
A method for the determination of sulphur in fly ash by instrumental proton activation analysis using the34S/p,n/34mCl reaction was developed. The 2128.5 keV and 3305.0 keV -rays of34mCl /t=32.0 min/ were measured on a Ge/Li/ -spectrometer, shielded with a lead absorber to attenuate low energy -rays. Irradiation and measuring conditions were optimized. The detection limit for instrumental analysis is 0.3 to 1 mg g–1 and the standard deviation is cca. 4% for a typical sample.
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.
Fast neutrons produced by irradiation of a thick beryllium target with 20–50 MeV deuterons are used for activation analysis.
The spatial neutron flux distribution around the target is measured. A rotating sample holder is used for the simultaneous
irradiation of samples and standards. Instrumental analysis can be applied for a number of elements. As an example, results
for calcium and strontium in some reference materials are given. The19F(n, 2n)18F reaction is used for the radiochemical determination of fluorine in rocks with a fluorine concentration ranging from 9 to