Performance of NAA Methods in an International Interlaboratory Reference Material Characterization Campaign

An extensive database of analytical results from a recent biological matrix Reference Material Characterization Campaign permitted an intercomparison of the performances of various methods among each other and with "true" best estimate concentration values established for these materials. Six different variants of neutron activation analysis (NAA) methods were employed including: instrumental neutron activation analysis, instrumental neutron activation analysis with acid digestion, neutron activation analysis with radiochemical separation, neutron capture prompt gamma activation analysis, epithermal instrumental neutron activation analysis, and neutron activation analysis with preconcentration. The precision and accuracy performance of NAA-based analytical methods are compared with three other major techniques, atomic absorption spectrometry (AAS), atomic emission spectrometry (AES) and mass spectrometry (MS) for 28 elements in 10 natural matrix materials.     

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.     

Fast neutron activation analysis of rare-earth elements in monazite from Korea

The relative ans single comparator methods have been applied to determine 7 rare-earth elements and U, Th in Korean Monazites by 14.5 MeV neutron activation analysis. The (n, 2n) nuclear reactions are used for all elements except La, for which (n, p) reaction is used. Al is used as a flux monitor for the relative method and as a singlle comparator for the single comparator method. The analytical results obtained by the two methods agree well within 3% deviation except for Sm and Gd. These results are also compared with the result obtained by a single comparator method using reactor neutron.     

Neutron activation analysis of the rare earth elements in rocks from the earth's upper mantle and deep crust

Three techniques for analyzing rare earth elements (REE) in geological materials are described, i.e. instrumental neutron activation analysis (INAA), neutron activation analysis with pre-irradiation chemical REE separation (PCS-NAA) and radiochemical neutron activation analysis (RNAA). The knowledge of REE concentrations in eclogites, peridotites and minerals from the earth's lower crust and upper mantle is very useful in constraining their petrogenetic history.     

Optimization of parameters of a system for continuous activation analysis of liquids

Mathematical considerations on the optimization of the flow and mechanical parameters of a system for continuous analysis of liquids are presented. The system in question contains a pump, an activation vessel placed in the vicinity of a neutron generator target, a pipeline and a vessel for the measurement of the induced activity. The following parameters of the system were taken into consideration: volumes of the activation and measurement vessels, position of the activation vessel with respect to the neutron generator target, shape of the activation vessel, and flow rate of the pumped fluid. The system is adapted for continuous and interrupted mode of operation of the neutron generator. The results of the theoretical considerations were verified in practice with the use of the above system and the reaction¹⁶O (n, p)¹⁶N. The agreement of theory and experiment was proved.     

Advances in 14 MeV neutron activation analysis by means of a new intense neutron source

A new intense 14 MeV neutron generator with cylindrical acceleration structure has been put in operation at the GKSS Research Center Geesthacht. The sealed neutron tube is combined with a fast pneumatic rabbit system with particular capabilities for neutron activation analysis involving shortlived reaction products. The sample transfer time is less than 140 ms. The maximum neutron flux available for activation is 5.2·10¹⁰ n/cm²s. Theoretical sensitivity predictions made in a previous study have been verified for some important trace elements. As a first application, samples of freeze-dried suspended matter and fishes of the Elbe river were analyzed.     

Photon activation analysis of coins and objects of art

Photon activation analysis is a suitable method for nondestructive analysis of Au, Ag and Cu because of the following advantages: the nuclear parameters (cross-sections, threshold energies) for the (γ, n)-reactions of the three elements as well as the attenuation coefficients of the activating bremsstrahlung and the emitted gamma radiation are quite similar. The severe self-shielding effects of thermal neutron activation analysis do not exist and these effects can be ignored or easily and accurately accounted for.     

Rapid multielement neutron activation analysis with a slowpoke reactor

The SLOWPOKE nuclear reactor meets many modern elemental analysis requirements; rapid multielement analysis of most types of samples is possible. The variable neutron flux (maximum 10¹² n cm^-2 s^-1) is stable, homogeneous and reproducible from day to day over a period of months. Sensitivities for 78 elements analyzed by neutron activation, with short irradiation and counting periods, have been determined; the conditions allow rapid multielement analysis with short sample turn-round time. Examples of the application of the technique to complex practical samples are given.     

Design and evaluation of a TNA explosive-detection system to screen carry-on luggage

Thermal neutron analysis (TNA) technology has been used for the non-destructive detection of explosives. The system uses a relatively weak ²⁵²Cf neutron source (1.03·10⁷ n/s) and two 3"×3" NaI(Tl) detectors. The presence of explosives is confirmed via detection of the 10.83 MeV prompt gamma-ray associated with nitrogen decay. The MCNP4A code was used to simulate the neutron and gamma transport through the system. The thermal neutron flux in the activation position was measured using gold and indium foils. The measured thermal neutron flux was lower, by not more than 9.5%, than that of simulation. In this report the results of the preliminary tests on the system are described.     

A new approach to single-comparator instrumental neutron activation analysis

A new parametric approach to single-comparator instrumental neutron activation analysis (INAA) at the University of Missouri Research Reactor (MURR) was investigated. A detailed MCNP steady-state model of the MURR core was developed using the latest neutron data libraries to compute the continuous-energy neutron flux distribution. Intrinsic reaction rates were predicted by coupling the computed local flux distribution to the isotopic (n, γ) excitation functions for a range of elements present in standard reference materials (SRM). Using the predicted (n, γ) reaction-rates, the concentrations for the various elements were determined. The method worked well for all nuclides tested, including those with cross sections that are not proportional to 1/v such as Lu and Eu with agreements for most elements within 5% of the reference value.     

Forty-five years of neutron activation analysis in Slovenia: achievements towards improved quality of measurements results

Main achievements towards improved quality of measurements results obtained by neutron activation analysis (NAA) at the TRIGA Mark II reactor of the Jožef Stefan Institute during its 45 years of continuous operation are reviewed from a historical perspective; emphasis is on the features specific for NAA. The development of radiochemical neutron activation analysis for characterising reference materials is described in detail in the first part. Several approaches specific for the method such as the determination of long-lived radionuclides, the simultaneous determination of several elements using double irradiation and the internal standard method are presented in more detail. Several interesting approaches such as combination with liquid scintillation counting detection and combination with radiometric measurements are outlined. Then, the development of instrumental neutron activation analysis, specifically the k ₀-NAA based method is discussed. The contribution towards methodological development of uncertainty assessment is outlined, and the importance of the nuclide-specific and neutron fluence-specific approach is emphasised. Throughout the paper, the importance of neutron activation analysis and contributions of measurements results obtained by this method to characterising (candidate) reference materials is shown.     

Destructive and nondestructive analysis of some elements in tissue and environmental samples by thermal neutron activation analysis technique

A rapid and selective method has been developed and applied for determining elements present in tissue and environmental samples by both destructive and nondestructive activation analysis. Nondestructive activation analysis involves the irradiation of the sample and standard of the elements such as Mn, Na, and K with thermal neutrons from²⁵²Cf neutron source followed by radioassay of the (n,r) products on a HPGe detector coupled to a PC-based MCA. Elements are determined by irradiating the samples in the thermal neutron flux of the CIRUS reactor and radiochemically separating the isotopes of interest using substoichiometric extraction and precipitation technique. The statistical evaluation of the method with respect to accuracy and precision of the method and its sensitivity are discussed.     

Determinations of silicon and phosphorus in rice planted in a district of high incidence of amyotrophic lateral sclerosis by neutron activation and X-ray fluorescence analyses

Silicon and phosphorus contents in polished and unpolished rice planted in a district of high incidence of amyotrophic lateral sclerosis (ALS) have been determined by neutron activation and X-ray fluorescence methods, and compared with those from control areas. In the neutron activation analysis, beta-ray spectra of 32P produced by the 31P(n, gamma)32P reaction on polished and unpolished rice were measured with a low background beta-ray spectrometer. In the X-ray fluorescence analysis, characteristic X-rays were analyzed with a wavelength dispersive X-ray fluorescence spectrometer. Silicon contents in polished and unpolished rice from the ALS area are 42 micrograms.g-1 and 370 micrograms.g-1, respectively, and the corresponding phosphorus contents are 1,210 micrograms.g-1, and 3,370 micrograms.g-1, respectively. The data for ALS area are equal to those for the control area within standard deviation.     

Effets de surface dans le dosage par activation neutronique du soufre

Surface effects in the determination of sulfur by neutron activation analysis Thermal neutron activation analysis leads to overestimated sulfur contents in some metals. This phenomenon was studied for samples of iron. It is attributed to ineffective chemical etching arising from dissolution of the metal through a surface layer which retains impurities, especially sulfur-35. Significant amounts of this isotope are produced at the surface through the ³⁵Cl(n, γ)³⁵S reaction. Experimental modifications which lead to the correct sulfur concentration are proposed.     

Determination of vanadium in high grade carbons by radioanalytical methods

The present work deals with the determination of vanadium in high grade carbons by three radioanalytical methods, viz. thermal neutron activation analysis with an accelerator, thermal neutron activation analysis with a reactor and proton induced X-ray emission analysis with an accelerator. It is cleared from this study that thermal neutron activation with an accelerator is more convenient for the rapid and non-destructive analysis of ppm-level vanadium in bulk carbons than thermal neutron activation analysis with a reactor. Proton induced X-ray emission is less useful for the analysis of bulk samples.     

Utilizing Distinct Neutron Spectra and a System of Equations to Differentiate Competing Reactions in Activation Analysis

In activation analysis, the continuous neutron spectrum produced in a nuclear reactor can be both beneficial and detrimental. A continuous spectrum allows for activation of particular elements by using any number of neutron energies. However, upper threshold energies exist for most elements where reactions other than an (n, ) absorption will occur. In this situation, two different parent nuclides can be activated to the same product, which creates a problem in performing a quantitative analysis of one or the other nuclide. A methodology is presented where a system of equations is used to solve for the quantities of both nuclides by using different irradiation ports, and using specific neutron filters to "customize" the neutron flux.     

Determination of cadmium in environmental materials by fast neutron activation analysis

Cadmium is determined by activation analysis with fast neutrons, obtained by irradiation of a thick beryllium target with 14.5-MeV deutrons. Cadmium-111m, formed via the ¹¹²Cd(n, 2n)^111mCd and ¹¹¹Cd(n, n′)^111mCd reactions, is separated by liquid—liquid extraction with zinc dithyldithiocarbamate in chloroform and measured with a Ge(Li) γ-spectrometer. For low concentrations, cadmium is precipitated as cadmium ammonium phosphate after the extraction. NBS and BCR reference materials were analyzed: for concentrations between 3 and 500 μg g^?1, the relative standard deviation ranges from 5 to 3% The results obtained for sewage sludge are compared with those obtained by reactor neutron activation analysis.     

Neutron activation analysis of iodine-129 and iodine-127 in environmental samples

The possibilities of reactor induced (n, p) reactions as a tool for neutron activation analysis of titanium in geological samples are discussed. The interference of calcium and scandium is experimentally evaluated. Results for Ti, Ca and Sc in GSP-1 and PCC-1 standard rocks are presented. On the basis of the experimental values, it is concluded that the⁴⁷Ti(n, p)⁴⁷Sc reaction is the most favourable for titanium determination.     

Use of D–T-produced fast neutrons for in vivo body composition analysis: a reference method for nutritional assessment in the elderly

Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the ³¹P(n,)²⁸Al reaction, and nitrogen for protein via the ¹⁴N(n,2n)¹³N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D–T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the quality of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment.