Epithermal neutron activation analysis using the monostandard method

A method is described for epithermal neutron activation analysis of 17 elements in granite rock samples using a single standard. Gold has been used as a single comparator due to its relatively high resonance integral value (I₀=400 barn). In addition, it is preferable to Co in order to obtain a large epithermal activation in a short irradiation. The method of calculation is simple and rapid and can be done using a small calculator. Epithermal activation is able to overcome the difficulty arising from changing irradiation position as well as increasing the number of determinable elements by eliminating the interference from undesired isotopes which have relatively high thermal cross section values (₀), when reactor neutron flux is used. The coupling of epithermal activation with the monostandard method has the advantage of using a small Cd-cover which overcomes most of the difficulties arising in the relative method with large volume cadmium filters.     

Instrumental neutron activation analysis of silicon wafers using the silicon matrix as the comparator

For the instrumental neutron activation analysis of trace impurities in high purity silicon wafer, a modified single comparator method has been applied. The energy distribution of the neutrons at the irradiation position was measured using the two flux monitors, Au and Co, and elemental contents were calculated using the silicon matrix in the wafer as a comparator. This has advantage of reducing the cross contamination from an external monitor during sample preparation and irradiation, the uncertainties from the non-homogeneity of the neutron flux and the error on the weight of comparators. Determination limits for 49 elements were presented under the condition of 72 hours irradiation at a neutron flux of 3.7·10¹³ n·cm^-2·s^-1 and 4000 s measurement. The analytical results obtained by this method and the conventional single comparator method were compared and were found to agree well within 5%.     

Comparison of neutron activation analysis methods

This work shows that nuclear data and neutron flux parameters can be applied to calculate directly the elemental concentrations. Techniques for extracting neutron flux parameters pertaining to the irradiation positions and nuclear data pertaining to the isotopes concerned from measured reaction rates have been previously developed. This method is compared to the comparator and relative methods of activation analysis. The principles, advantages and disadvantages of each method and sources of errors are discussed. It also briefly discusses other factors such as accuracy and precision, sensitivity, detection limits and limit of quantitative determination. The three methods are applied to the analysis of five environmental reference materials. The concentrations of more than 20 elements are determined. The results show a good agreement with the certified and/or literature values.     

Multi-elemental epithermal neutron activation analysis using an internal single comparator

Epithermal neutron activation analysis using an internal single comparator has been used for the analysis of Saudi Arabian iron ores. The concentration of thorium, barium, terbium, tantalum, cobalt, lanthanum and antimony was determined using iron in the ore as an internal comparator for all the elements. In case of antimony there was an agreement between this method and the conventional method indicating that the given method is accurate.     

k0 Standardization Approach in Neutron-Induced Prompt Gamma-Ray Analysis at JAERI

The k ₀ standardization method has been studied and applied at JAERI for the accurate determination of multielements by neutron-induced prompt gamma-ray analysis (PGA). The k ₀ factors for 26 elements using Cl as a comparator were measured by the cold and thermal neutron guided beams of JRR-3M with an uncertainty less than 3% except for a few elements. The k ₀ factors for most elements obtained with both cold and thermal neutrons agreed within 3%, and agreed also with those measured at other cold and thermal neutron guided beams within 10%, except for a few elements. Multielement determinations in reference materials were performed using the k ₀ factors obtained to evaluate the accuracy and precision of this work.     

The k0-method in cold-neutron prompt gamma-ray activation analysis

The k ₀-standardization method has been applied and evaluated at the cold-neutron prompt gamma-ray activation (PGA) facility of the Swiss spallation source SINQ (Paul Scherrer Institute). The k ₀-factors for 26 elements of interest were measured using chlorine as a comparator. The results showed good agreement with the values determined at other cold and thermal neutron guided beams, except for a few elements. Then, standard reference materials were analyzed to assess the accuracy of the method using the obtained k ₀-factors. Finally, the technique was used for multielement determination in various samples coming from nuclear waste storage, geochemistry and geology. In addition, the non-destructive nature of PGAA offered an interesting application in archeology.     

Reactor neutron activation analysis by a triple comparator method

The single comparator method has been extended to a triple comparator method, using⁶⁰Co,^114m In 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)^114m In have been determined.     

Multi-element analysis of japanese tea leaves by neutron activation analysis and the single comparator method

The reliability of the single comparator method in neutron activation analysis has been studied by comparing the calculated and experimental k values and by determining the concentration of trace elements in iron. The method has been applied to the analysis of tea leaves for thirteen elements; their concentrations varied over five orders of magnitude.     

Neutron activation method for nitrogen determination in biological specimens

For the determination of the nitrogen content in plants, 14 MeV neutron activation analysis was used based on the determination of the elemental concentration by measuring the area of the gamma-radiation of the radionuclide¹³N as a result of¹⁴N(n, 2n)¹³N reaction. Three methods were tested in order to obtain quantitative results: comparator method, method for absolute determination of the neutron flux and monitor method. Using the monitor method, results for nitrogen content in plant species were obtained-for beans 74.8% and for maize 1.8%. The precision of determination is ±10%. The possible sources of errors are analyzed. The efficiency of the Ge(Li) detector has been determined using a combined -source in the energy interval 120–1400 keV with precision of 4.5%. The sensitivity achieved was 4 mg or 47 imp/mg per min.     

Comparison of routine INAA procedures based on k0 and kZn standardizations

Performance characteristics (especially accuracy) of a routine INAA with k₀ standardization were verified and compared with those of INAA with a classical single comparator. For this purpose, samples of three certified reference materials of environmental origin (Fly Ash, Orchard Leaves and Buffalo River Sediment—all supplied by NIST) were irradiated with both kinds of comparators (Au–Zr for k₀ and Zn for classical k method) in one irradiation rabbit. Also the following steps of INAA procedure were practically the same for both standardization methods used (counting, spectral processing, etc.). The results have shown that the k₀ method gives sufficiently accurate results comparable with those of the well established and routinely used single comparator (Zn) method, provided proper neutron flux monitoring, efficiency calibration and also coincidence summing corrections are applied. This work shows that modern k₀ standardization method in INAA can be sucessfully used in routine practice and applied with an advantage in INAA laboratories subject to changes of neutron spectra or counting conditions.     

Determination of impurities in titanium and titanium oxide by radiochemical neutron activation analysis

A radiochemical neutron activation analysis has been applied to 2N–4N grade titanium metal and its oxide. Twenty two impurities were separated in a group from scandium by a radiochemical separation method using cation exchange resin with HBr and HCl. The contents of the elements were calculated by a single comparator method using two monitors. The analytical results agree well within 10% deviation with those obtained by instrumental method. Eighteen elements, Na, Fe, Co, As, Se, Sr, Mo, Sb, La, Eu, Tb, Yb, Lu, Hf, Ta, W, Th and U, are determined in titanium oxides and 17 elements, Na, Cr, Fe, Co, Se, As, Zr, Mo, Sb, Cs, Ce, Tb, Yb, Hf, Ta, W and Th, in titanium metals.     

Trace element determination in high-purity aluminum clad samples by k 0-based internal monostandard instrumental neutron activation analysis

The k₀-based internal monostandard instrumental neutron activation analysis (IM-INAA) method was applied for quantification of trace impurities in seven high purity aluminum samples used as fuel cladding in a research reactor. Samples along with BCS CRM 182 (Si–Al alloy) were irradiated in high flux reactor neutrons for 10–15 h. In situ detection efficiency, needed in concentration calculation ratio by IM-INAA, was obtained using gamma rays of activation products produced in the samples. Elemental concentration ratios obtained with respect to Fe (used as internal monostandard) were converted to absolute concentrations by determining concentration of Fe by relative method of NAA. Concentrations of ten trace elements (Sc, Cr, Co, Zn, Ga, La, Ce, Sm, W and Hf) including major element Fe were determined in this work. The method used is non-destructive in nature and does not need multielement standards. Results of IM-INAA were compared with those obtained by relative method of INAA and inductively coupled plasma atomic emission spectrometry (ICP-AES). Details of methodologies and results obtained by all methods are discussed and compared in the paper.     

Application of k0-based internal mono standard instrumental neutron activation analysis method method for composition analysis of stainless steel clad sample

The k₀-based internal mono standard instrumental neutron activation analysis (INAA) method was used for the composition analysis of some irregular shape stainless steel (SS) samples of type SS 316M, which is used as fuel cladding in Indian fast breeder test reactor (FBTR). The method utilizes in situ relative detection efficiency using γ-rays of the activation products present in the sample for overcoming γ-ray self-attenuation. Samples were neutron activated using the thermal column as well as the core position of the reactor and the assay of radioactivity was carried out by high-resolution gamma ray spectrometry. The elements determined were Fe, Cr, Ni, Mo, Mn, Co, Cu, As and W. Since all the major elements (Fe, Cr, Ni, Mo and Mn) were amenable to NAA, the relative elemental concentrations with respect to Fe, obtained by this method, were converted to their absolute values by mass balance. The results were compared with specified compositions and found to be satisfactory. In order to validate these results obtained by the standard-less approach, sub samples of SS 316M in solution forms were analyzed by prevalent relative and k₀ methods of INAA, and results were found to be in good agreement. The accuracy of the internal mono standard INAA method has been evaluated by analyzing an alloy steel certified reference material, CRM 225/1 of British Chemical Standards (BCS).     

Activation analysis of high-purity silicon

The triple comparator method is used for the analysis of impurities of high purity silicon by neutron activation. The ratios of the specific photopeak activities of the isotopes investigated to the specific photopeak activities of the gold, indium and cobalt comparators were determined. The triple comparator method avoids some tedious problems in the multi-element activation analysis and it is very well suited for the determination of ‘non-expected’ elements. Research associate of the N. F. W. O.     

The determination of ko factors and their application to the neutron activation analysis of pure zirconium metal by the single-comparator method

The procedures followed for the determination of standardization factors and their use in the single-comparator method for multi-element reactor neutron activation analysis are described. The method is applied to the determination of Cr, Mn, Fe, Ni and Mo in pure zirconium metal. The matrix could serve as the single comparator and as a bi-isotopic thermal-to-epithermal neutron flux ratio monitor.     

The internal comparator method

An internal comparator method is proposed which offers reliable instrumental neutron activation analysis (INAA) results for samples with an irregular geometry and/or measured at the closest position to the Ge detector. Because the selected internal comparator in the sample analyzed will receive exactly the same thermal neutron flux as the other components, this method can be applied to the INAA of materials suffering from thermal neutron self-shielding. To apply the internal comparator method, the k₀-method must be installed and the analytes, including the internal comparator, should be homogeneously distributed in the test portion.     

Thermal and epithermal neutron activation analysis using the monostandard method

A new approach is presented for neutron activation analysis using the monostandard (single comparator) method. Elements to be determined are classified into two groups; those with σ_o>I_o are activated with whole neutron spectrum (without Cd-cover), using a standard of the same group (e.g. Sc), while elements with I_o>σ_o are activated with epithermal neutrons (under Cd-cover) using a standard of the same group (e.g. Au or Co). Epithermal activation increases the number of determinable elements and its coupling with the monostandard method has the advantage of using a small Cd-cover. The σ_o and I₀ values of some elements were determined to test this approach.     

Determination of trace elements in reference materials by the k(0)-standardization method (INAA)

Instrumental neutron activation analysis was applied to four reference materials: NBS 1573 (Tomato Leaves), NBS 1645 (Citrus Leaves), NBS 1645 (River Sediment), and IAEA MA-A-2 (TM) (Fish Flesh). The k(0)-standardization method was used. The results are compared with (i) reference values (mostly non-certified) and (ii) published values obtained by other methods. Good agreement is found for most of the elements. For some elements, large discrepancies are observed.     

Neutron activation analysis without multielement standards

A physical approach is described for instrumental multielement activation analysis with whole neutron spectrum (without Cd-cover) using the monostandard (single comparator) method. To test the capabiliteries of this method, 15 samples representing different Egyptian granite rocks were analyzed. As many as 21 trace elements beside Fe, K and Na were determined. Calculation of the experimental data has been done using the Gamma-Monostandard Analysis program with the Commodore Computer available at the Institute of Radiochemistry at Garching near München. The accuracy of the method for nondestructive multielement analysis agrees within 3% with the relative method using multielement standards.     

Determination of Essential Elements in Ayurvedic Medicinal Leaves by k0 Standardized Instrumental Neutron Activation Analysis

Elemental concentrations of a few medicinal leaves are determined by instrumental neutron activation analysis using the single comparator (k ₀) method. Data obtained for neem leaves, collected from two different places, have been used to see the effect of soil condition. The applicability of the method particularly for the simultaneous determination of Ca, Mg, V and Al in biological matrices has been evaluated in terms of the detection limit, precision and accuracy. The method was validated by analysing the NIST Standard Reference Material (SRM-1571) and it was found that the elemental concentrations measured in SRM-1571 are within ±10% of the reported values.