Inteferences in neutron and photon activation analysis

The effect of following interferences was quantitatively assessed in terms of interference factor by irradiating samples together with highly pure reagents at two reactor sites of diferent neutron spectra and fluxes for neutron activation analysis (NAA) and an electron LINAC for photon activation analysis (PAA). The interfering reactions studied are 91) fast neutron-induced reactions, (2) uranium fission (3) (n,γ) reactions of other target elements in NAA, and (4) reactions induced by secondary neutrons in PAA. Corrections for these interferences were successfully applied to the activation analysis of some geological reference rock samples and biological samples.     

Comparison of the role of photon and neutron activation analyses for elemental characterization of geological,biological and environmental materials

The potential of photon activation analysis (PAA) for multielement trace analysis can hardly compare with that of neutron activation analysis (NAA). However, PAA appears superior over NAA for the determination of a number of elements, namely C, N, O, F, Mg, Si, Ca, Ti, Ni, Sr, Y, Zr, Nb, Sn, Tl and Pb in geological, environmental and biological materials. Most of these and other elements can be determined using nondestructive, instrumental PAA (IPAA), especially in geological materials. The possibilities of IPAA for multielement analysis using photoexitation and other photonuclear reactions are reviewed and compared with those of instrumental NAA (INAA), namely for geological materials. The need for and usefulness of radiochemical PAA (RPAA) procedures are also discussed.     

Tables of nuclear constants for gamma activation analysis

Tables of nuclear data were compiled for the purpose of routine gamma (photon) activation analysis. The tables are arranged in two parts. The first one lists the readionuclides in order of their atomic number. In the second one, the emitted gamma-ray photons are tabulated in order of increasing energy. Tables contain the gamma emitters produced by the following photonuclear reactions: (γ, γ), (γ, n), (γ, p), (γ, p+n), (γ, 2n), (γ, 3n), (γ, 4n), (γ, 2p), (γ, α), (γ, α+n), (γ, α+p). This set corresponds to the maximum energy of the bremsstrahlung of roughly 45 MeV. The program for output of the tabulated data is made such that it is possible to reduce the data as required for specific irradiation and measuring conditions (reaction thresholds, energy and intensity of gamma-rays, half-lives and target elements).     

A compilation of photonuclear reaction products and associated gamma-energies

High-energy bremsstrahlung from high-intensity electron linacs can produce activation through a variety of photonuclear reactions. A great range of activities by half-lives can be used. Some discrimination between target elements can be obtained through the choice of bremsstrahlung end-point energy. The high resolution of Ge(Li) gamma-ray spectrometers permits much of the analysis to be accomplished without chemical separation of resulting nuclei; hence, non-destructive analysis can be applied to many materials. To facilitate the use of such analysis, a compilation of photonuclear reactions with their resulting gamma-rays has been prepared.     

Neutron activation analysis by combined capture and decay gamma-spectrum method

The usual method of the neutron activation analysis is performed by the measurement of the characteristic nuclear radiations of the produced radioactive isotope by neutron irradiation. An advance in this field has recently been proposed in which the prompt capture γ-rays are observed in addition to the nuclear radiation of the produced nucleus. The characteristic energy spectra of these two kinds of γ-radiations are the main basis for the combined activation analysis method. The experimental setup consists of a γ-radiation pulse height energy spectrum system which is synchronized with a pulsing neutron generator of ‘D—T’ or ‘D—D’ reaction. The present results indicate that a qualitative and semi-quantitative determination of a number of elements is feasible, with an overall error of 10–15%.     

Non-destructive multi-element photon activation analysis of river sediments

A large number of toxic elements, including Th and U, in Scheldt and NBS river sediments, have been determined non-destructively by high energy photon activation. The length of irradiation varies between 1.5 hours for short lived-nuclides and 7–18 hours for long lived-nuclides. The induced activities are measured using a single open-ended coaxial Ge(Li) detector and the photopeak integrations are calculated using the total peak area method and the Cutipie computer program after substraction of the intrinsic background of the detector from each spectrum (Angela program). The photonuclear reactions and the best detection limits for 36 elements are indicated.     

Yields of photonuclear reactions for photon-activation analysis with high-energy bremsstrahlung

Experimental reaction yields have been determined for various types of photonuclear reactions, induced in 52 elements by means of Bremsstrahlung irradiation with maximum energies ranging from 30 to 72 MeV, and of detection of the resultant activities with a lithium-drifted germanium detector. From the results obtained, sensitivities in photon-activation analysis were evaluated and the reactivity of high-energy photons with nuclei in a wide range of atomic number is discussed. Some nuclear considerations in photon-activation analysis, involving the relative probability of forming each product as a result of the (gamma,xnyp) reactions are also given.     

Quantitative evaluation of interference reactions in photon activation analysis

Interferences of different types (competing reactions, overlapping photons emission energies etc.) occur more frequently during activation analysis with high energy exciting radiation that in conventional thermal neutron activation. Three main types of interference in high energy photon activation analysis (PAA) have been determined quantitatively, using experimentally obtained data exclusively. Based on the results presented, it is possible in many critical cases to improve significantly the accuracy of analysis results obtained by PAA.     

Investigations on the comparator technique used in epithermal neutron activation analysis

The possible extension of the comparator technique of reactor neutron activation analysis into the field of epithermal neutron activation has been investigated. Ruthenium was used for multi-isotopic comparator. Experiments show that conversion of the so-called reference k-factors—determined by irradiation with reactor neutrons—into k_epi-factors usable at activation under cadmium filter, can be evaluated with fair accuracy. Sources and extent of errors and their contribution to the final error of analysis are discussed. Based on the paper presented at the 2nd European Conference on Analytical Chemistry, 25–30 August, 1975, Budapest, Hungary.     

Determination of trace amount of nickel in cosmic spherules by photon activation analysis

Trace amount of nickel in high-purity iron and iron oxide samples was determined by photon activation analysis (PAA) using the Electron Linear Accelerator at the Research Center for Electron Photon Science, Tohoku University. It was confirmed that about 0.015 μg of nickel in the high-purity iron oxide sample could be determined with an experimental uncertainty of 20% by PAA, that is, it was possible to determine 1% of nickel at least in a few μg of cosmic spherules. PAA was applied to the nickel-determination in cosmic spherules. Nickel in cosmic spherules was determined by PAA more accurately than by instrumental neutron activation analysis done in a reactor neutron spectrum with the fluence rate ratio of thermal neutrons to fast of 4–5 which has so far been applied to the analysis of spherule samples. Additionally, trace amount of nickel in the reference material Giant Clam JCt-1 supplied by the Geological Survey of Japan was determined by PAA with radiochemical treatment.     

Instrumental multielement activation analysis of soil samples

Soil samples from a waste water cleaning facility in Berlin, Germany, have been analyzed using several activation analysis methods. 43 elements have been determined by instrumental high energy photon activation analysis (PAA), instrumental thermal neutron activation analysis (NAA) and 14 MeV neutron activation analysis (fNAA). Conventional gamma ray spectroscopy and low energy photon spectroscopy (LEPS) have been applied for product activity measurement. It has turned out that these methods in combination offer a wide spectrum of analytical information.     

Application of bremsstrahlung activation analysis for the determination of carbon and nitrogen in sodium

Carbon and nitrogen are determined by means of the photonuclear reactions:¹²C(γ n)¹¹C and¹⁴N(γ, n)¹³N. This article presents a simultaneous chemical separation method for the isolation of¹¹C and¹³N. It is based mainly on combustion of the sample, after irradiation and etching, in a mixture of oxidising acid fused salts (B₂O₃ and Pb₃ O₄) containing a dispersing agent (NaCl and KCl) and the respective carriers. Each analysis takes about 40 min altogether. Minimum carbon and nitrogen contents of a few 10⁻² μg·g⁻¹ can be measured. The influence of the main competitive nuclear reactions on neighbouring elements, including the sodium itself, is examined.     

Calculation of primary nuclear interferences occurring in neutron activation analysis with a slowpoke reactor

The cross-sections for (n, p) and (n, α) reactions which may interfere with (n, γ) reactions used in thermal neutron activation analysis have been calculated systematically using an empirical formula in conjunction with published σ-values. The interference factors (IF) have been subsequently calculated for flux conditions that prevail in a SLOWPOKE II reactor and both cross sections and interference factors have been listed in a tabulated form. The significance and usefulness of IF's thus obtained is discussed from the standpoint of trace analysis. For a number of low-Z matrices, their magnitude is such that the measurement of certain constituents at the ppm level by instrumental analysis is rendered virtually impossible, as for the following matrix—trace element pairs=Al/Mg, Na/Al, P/Si, S/P and Cl/S. For higher Z elements, interferences can be neglected in most instances.     

Different methodologies in neutron activation to approach the full analysis of environmental and nutritional samples

Different methodologies of neutron activation analysis (NAA) are now available at the Technological and Nuclear Institute (Sacavém, Portugal), namely Compton suppression, epithermal activation, replicate and cyclic activation, and low energy photon measurement. Prompt gamma activation analysis (PGAA) will be implemented soon. Results by instrumental NAA and PGAA on environmental and nutritional samples are discussed herein, showing that PGAA — carried out at the Institute of Isotope Research (Budapest, Hungary) — brings about an effective input to assessing relevant elements. Sensitivity enhancement in NAA by Compton suppression is also illustrated. Through a judicious combination of methodologies, practically all elements of interest in pollution and nutrition terms can be determined.     

Application of neutron activation analysis to determine the contents and isotopic ratios of elements in rocks and minerals

Data on the applicability of neutron activation analysis to determine various rare and trace elements and the isotopic abundance of some of them in natural samples are discussed as relevant to the solution of various geological and geochemical problems. For the determination of minute amounts of elements from small weighed quantities of rocks and minerals a number of modifications of neutron activation analysis are used: analysis with the radiochemical separation of individual elements—RNAA (tantalum, tungsten, antimony, arsenic, molybdenum, rhenium, osmium, etc.) and analysis with semiconductor—Ge (Li)—gamma-spectrometry, which is multi-element and non-destructuve—INAA (scandium, europium, tantalum, iron caesium, rubidium, cobalt, antimony, etc.) or the combination of the latter with group radiochemical separation—IRNAA (alkaline, alkaline-earth, rare-earth elements, etc.). First steps have been made towards developing techniques for the determination of the isotopic rations of some elements by means of neutron activation method, e.g., the isotopic ratio of⁵⁸Fe/⁵⁴Fe. The accuracy of isotopic ratio determination is 1 to 3 relative per cent.     

Recoil properties of radionuclides formed in the photonuclear reactions onnatCu at intermediate energies

The recoil properties of 26 radionuclides produced in the photonuclear reactions on Cu at bremsstrahlung end-point energies (E ₀) of 250 to 1000 MeV have been investigated using the thick-target thick-catcher method. Kinematic properties of the product nuclei were calculated by the two-step vector velocity model. The calculated mean kinetic energies,T, of product nuclei increase with increase of the mass difference between products and target, reflecting the resonance natures and absorption mechanisms. TheT atE ₀≥600 MeV were well reproduced by a calculation performed by PICA code byGabriel andAlsmiller atE ₀=400 MeV, except for (γ,xn) products by giant-resonance.     

Charged particle activation analysis coupled with X-ray counting

A survey is given on the analytical use of X-ray emitting radioisotopes produced by charged particle activation. Thirty-nine proton and deuteron reactions were considered on twentysix elements (34≤Z≤82). Thick target yields and sensitivity estimates are presented. The features and limitations of this method and the scope of non-destructive and destructive determinations are discussed. The main interest of this approach is to open an avenue for trace analysis with simplified data acquisition and reduction.     

Nuclear reaction analysis of boron and oxygen in silicon

The main characteristics of analysis by the nuclear method at low energy are summarized. The experimental set-up, and especially the target chamber arrangement are shown. Nuclear analyses of boron and oxygen in a silicon substrate are presented; sensitivity, accuracy and competing reactions have been studied. The analysis of boron and oxygen is possible, although these elements give interfering reactions. Results concerning homogeneity in the sample surface (for diffused or implanted boron), a diffusion study (SiO₂−Si exchange) and profile measurements are presented.     

Synthesis and characterization of inclusion complex of the vasodilator drug minoxidil with β-cyclodextrin

The inclusion complex of β-cyclodextrin and minoxidil (2,4-diamino-6-piperidinopyrimidine 3-oxide) was synthesized using two methods—kneading and freeze-drying—and characterized by UV-Vis spectroscopy, infrared spectroscopy, powder X-ray diffractometry, differential scanning calorimetry, thermal gravimetric analysis, and nuclear magnetic resonance spectroscopy. These techniques have demonstrated the existence of inclusion compound formation between the host and guest with a molar ratio of 1:1. The studies of solubility and the data obtained by nuclear magnetic resonance spectroscopy showed a weak interaction between the guest and the cyclodextrin molecules in solution.     

Comparison of photon activation analysis with other modern analytical methods as tools for the solution of actual analytical problems

A 35 MeV linear electron accelerator is used to investigate how far photon activation analysis can be used within the broad spectrum of analytical methods applied in BAM. The irradiation facilities are described. Examples are given for the application of PAA in the analysis of oxygen in metals and compared with conventional heat extraction and other nuclear analytical methods. It is further shown that PAA is a very useful tool for the analysis of traces of noble metals in Cu compared with other methods. Finally the possibilities of PAA in the field of multielement analysis are demonstrated taking ancient roman potsherds and bronze as examples. The results are compared with those of XRF and AAS. It is concluded that PAA is a valuable tool in the analysis of light elements with at least partly unique possibilities, that it can serve as an independent method for the certification of Reference Materials in many cases and that PAA can be very useful applied for multielement analysis.