The internal standard method coupled with the standard addition method has been applied to the analysis of environmental materials, such as urban particulate matter, vehicle exhaust particulates and coal fly ash by photon activation. High-resolution gamma-ray spectrometry makes possible to use multi-internal standard gamma-rays, in order to crosscheck the analytical results obtained from each internal standard. It was ascertained that this method can provide not only accurate analytical results but also the information of homogeneity of samples, correlation of elements in the sample, loss or contamination in the preparation process.
A method has been developed where the element to be determined in the sample consists of at least two stable isotopes, which are easily converted to radionuclides through particular nuclear reactions. The sample is previously processed by adding a known quantity of an enriched isotope of the element, while the comparative reference is prepared by taking an arbitrary amount of the natural element under investigation. The usefulness of the method was verified by photon activation analysis of strontium in standard reference materials of tomato and citrus leaves, using isotopically enriched86Sr as a spike, and the accurary and precision of the method were proved to be valid.
In order to apply the stable-isotope dilution method to charged-particle activation analysis, determination of strontium in biological materials has been studied by proton activation using isotopically enriched86Sr as a spike. To avoid thermal decomposition of biological materials due to the low penetrating power of proton beam, and to eliminate interfering nuclear reactions due to the matrix elements, strontium in the sample and/or isotopic mixture as a comparator was separated chemically together with most of calcium before bombardment, and the fraction isolated was converted to a silica-gel pellet as a most suitable physical and chemical form for bombardment. By processing as above, it was demonstrated that the strontium contents in the biological materials can be determined accurately, precisely and easily. Through a series of experiments, the method was also proved to be applicable for charged-particle activation analysis.
In order to study the application of the new developed internal standard method to charged-particle activation analysis, simultaneous determination of Ti, Cr, Fe, Cu, Ga and Zr in several commercial aluminium alloys has been tried using the respective proton-induced reactions. As a result, it could be proved that the best precision and accuracy are also obtained in these determinations.
A new internal standard method for activation analysis has been developed. This method is characterized by that a suitable element present originally in the sample is used as an internal standard and the comparative standard is prepared by applying the standard addition method to the duplicated sample. When a sample under examination contains Wag of trace element A to be determined together with a known amount of element B which is usable as an internal standard, and when the comparative standard is prepared by adding W
g of accurately known small amount of the element A to the duplicated sample, even if the sample and comparative standard are irradiated separately by particles with different fluxes, Wa can be determined, easily by using the following equation: Wa=W
/AR)-1] Where AR and A
are counting ratios of gamma-rays emitted by two radioactive nuclides produced from the element A and B in the sample and comparative standard, respectively. Neither correction of the inhomogeneities of flux between the sample and comparative standard, nor that of, the self-shielding effects are necessary for the present method. The usefulness of the method was examined through the determination of Co, Ni, Rb and Sr in pepperbush by means of photon activation, and the precision and accuracy of the method were proved to be valid.
A new internal reference method for activation analysis has been developed. The method can be used effectively for special samples in which suitable elements as internal standards are absent and the self-shielding effect can be neglected. In this method, Wb g of element B as an internal reference is added to the sample which contains Wa g of element A to be determined, whereas the comparative standard is prepared by mixing only the element A and B in a known concentration ratio of W
/Wb. When the sample and comparative standard are irradiated by particles with the same energy distribution, even though both are irradiated separately by particles with different flux, Wa can be determined easily by the following equation.
where Ag and AR are count ratios between gamma-rays emitted by two radioactive nuclides produced from elements A and B in the sample and comparative standard, respectively. The usefulness of the present method was examined through the determination of Ti, Cr, Ni and Zr in several commercial aluminium alloys by means of photon activation, and the accuracy and precision of the method were verified.
The combined use of photon activation and γ-γ coincidence spectrometry is described for the useful and selective nondestructive
determination of nickel in geological materials. This method is characterized by the utilization of the nuclide emitting β+ particles in its decay and γ-γ coincidence counting with two gates: one for the annihilation photopeak region and the other
for the higher Compton plateau region. The practical detection limits by this method for nickel, arsenic, rubidium, sodium
and scandium in silicate matrices could be set at 2.0, 1.2, 9.0, 110 and 1.4 μg, respectively.
Charged particle activation analysis of phosphorus in biological materials using the31P (α,n)34mCl reaction has been studied. Since34mCl is also produced by the32S (α,pn) and the35Cl (α, α′ n) reactions, the thick-target yield curves on phosphorus, sulfur and chlorine were determined in order to choose
the optimum irradiation conditions. As a result, it was found that the activation analysis for phosphorus without interferences
from surfur and chlorine is possible by bombarding with less than 17 MeV alphas. The applicability of this method to biological
samples was then examined by irradiating several standard reference materals. It was confirmed that phosphorus can readily
be determined at the detection limit of 1 μg free from interferences due to the matrix elements.
As a new method, stable-isotope dilution activation analysis has been developed. When an element consists of at least two
stable isotopes which are converted easily to the radioactive nuclides through nuclear reactions, the total amount of the
element (xg) can be determined by irradiating simultaneously the duplicated sample containing small amounts of either enriched
isotope (y g), and by using the following equation.
Where M and M* are atomic weights of the element to be determined and the enriched isotope used as a spike,θ1 andθ2 are natural abundances of two stable isotopes in the element,θ1*
are isotopic compositions of the above isotopes in the enriched isotope, and R and R* are counting ratios of gamma-rays emitted by two radionuclides produced in the sample and the isotopic mixture. Neither calibration
standard nor correction of irradiation conditions are necessary for this method. Usefulness of the present method was verified
by photon activations of Ca, Zn and Ce using isotopically enriched48ca,68Zn and142Ce.
In order to study further the applicability of the newly developed stable isotope dilution method, simultaneous determination of Ca, Rb, Sr and Ce in three kinds of environmental materials has been tried by means of photon activation using isotopically enriched48Ca,87Rb,86Sr and142Ce as spikes. All determinations were demonstrated to be sensitive, highly specific and reasonably accurate.