Analytical applications of delayed and instrumental neutron activation analysis

Delayed neutron activation analysis (DNAA) is a rapid and sensitive analytical method for the determination of fissile elements in a variety of samples. The present work describes two different analytical applications of delayed neutron activation for the analysis of biological and environmental samples, respectively. In the first application, DNAA was utilized to determine the natural uranium content in NIST standard reference materials (SRM) 1547 peach leaves and 1573a tomato leaves. Measured uranium mass fractions are comparable to the non-certified values listed on the certificates for these materials. In the second application, delayed neutron activation is coupled with instrumental neutron activation analysis (INAA) for the measurement of rare earth elements (REE) (cerium, lanthanum, neodymium, and ytterbium) in NIST SRM 2586, Trace Elements in Soil Containing Lead from Paint. DNAA was utilized to determine the uranium mass fraction in SRM 2586 for the subsequent application of a correction factor to account for cerium, lanthanum, and neodymium produced as part of the INAA irradiation. Measured and corrected mass fractions for the REEs described here are all within the uncertainty limits provided on the NIST certificate for SRM 2586. These results and the demonstrated sensitivity of the DNAA system establish and validate the use of this method for the determination of REEs and for potential nuclear forensics applications.     

Erros in instrumental neutron activation analysis

Equations are derived for the statistical and systematic error in INAA. It is possible to use them for the definition of limits of decision, detection and determination.     

Errors in instrumental neutron activation analysis

Equations are derived for the statistical and systematic error in INAA based on single photopeaks. They may serve to predict the applicability of the method or to judge data obtained under well-known conditions.     

Multielement analysis of lichen by instrumental neutron activation analysis

Lichen (species Trypethelium Eluteriae) is analysed for different elements. Nondestructive instrumental neutron activation analysis is employed for the multielemental analysis. Gamma-ray spectrometry is used for the identification and quantitative estimation of elements. Concentrations of 24 elements are reported. Gamma-ray spectrum of the lichen irradiated for 16 hours, delayed for 10 days, and counted for 10 hours on a 50 cm³ coaxial Ge(Li) detector is given.     

Elemental analysis of limestone by instrumental neutron activation analysis

Limestone samples from Assuit Governrate in Upper Egypt were subjected to elemental analysis by instrumental neutron activation analysis and X-ray fluorescence techniques. The samples were properly prepared together with their standards and simultaneously irradiated in a neutron flux of the order 7 × 1011 n/cm² s using TRIGA research reactor at Mainz. After activation the samples were subjected to γ-ray spectrometry using a high purity germanium detection system and computerized multichannel analyzer. Nineteen elements: Na, Ca, Mn, Fe, Sc, Cr, Co, Zn, Sn, La, Ce, Nd, Eu, Sm, Yb, Lu, Hf, Th and U were analyzed. X-ray fluorescence spectrometry have been also used. The presence of any elements in higher or lower levels in certain limestone samples is contingent on the occurrence of its bearing minerals, nature of parent sediments and depositional environments of these sediments. The major elements in the samples were also observed to be among the elements that had high enrichment factors in the study of suspended dust particulate within and around cement industries. This confirms cement as the major contributor to the airborne particulate matter in the environs.     

Multielemental analysis of soils by instrumental neutron activation analysis

The results of an instrumental neutron activation analysis of some elemental concentrations in different soil samples near the industrial areas at Tirupati, India, are reported. Altogether 14 elements, Sm, La, Cr, Co, Zn, Cs, Ce, Th, Rb, Na, K, Sr, Fe and Eu were determined. The samples were irradiated with neutrons at the 100 kW Triga - Mainz research reactor and the induced activities were measured by gamma-ray spectrometry using an efficiency calibrated high resolution high purity germanium (HPGe) detector in connection with a multichannel analyzer. The results are discussed.     

Determination of lithium by instrumental neutron activation analysis

The fast transfer system in the DR 2 reactor for irradiation at a thermal neutron flux density of 10¹³ n·cm⁻²·sec⁻¹ was used for the determination of lithium by the⁷Li(n, γ)⁸Li reaction. β-counting with a large perspex Cerenkov detector begun at 0.3 s after the end of irradiation, and multi-scaler data was accumulated in 300 channels at 0.1 s per channel. With a suitable choice of discrimination level only¹⁶N and background interfere, and the 0.84 s half-life of⁸Li was resolved by the method of weighted least squares. Results are presented for 36 international geochemical reference materials, and for a few biological samples, including BOWEN's kale and the NBS Standard Reference Material 1571 Orchard Leaves.     

Multielement instrumental neutron activation analysis of silver-copper coins

Neutron activation, applied to silver and copper based coinage, leads to a measure of the mean concentrations of major and 12 trace elements, even if their distribution is heterogeneous. The drawbacks of this activation method applied to such a matrix are shielding effects and high radioactivity of major elements. Both effects were avoided by accurately calculating the correction coefficients and by choosing the optimal working conditions. Analytical results obtained lead to a better knowledge of the chronology and origin of Armorican protohistorical coinage.     

Human hair instrumental neutron activation analysis and medicine

Periodically increasing and decreasing enthusiasm has accompanied the studies of medical significance of human hair elemental composition for at least two decades. In this field, nuclear analytical methods play an extremely important role, especially the instrumental neutron activation analysis (INAA). This paper tries to add some new knowledge to this problem. Two approaches are used — comparison of individual hair composition with certain diagnoses in clinic groups and comparison of population data with medical statistics. Rather large samples and multielement mathematical procedures helped reveal strong correlations valuable for diagnostic and health screening.     

Trace-element analysis of argyle diamonds using instrumental neutron activation analysis

Thirty four elements were determined by instrumental neutron activation analysis in colourless, brown, and pink diamonds, with and without inclusions. These were compared with data obtained for similar elements in the host lamproite rock. The natural radioactivity of these samples was measured by instrumental techniques, and found to be negligible.     

Multi-element analysis of soils by computerized instrumental neutron activation analysis

The applicability of instrumental neutron activation analysis (INAA) for soils is described and demonstrated and its restrictions mentioned.     

Multielement analysis of food spices by instrumental neutron activation analysis

Twenty-four elements in six food spices were estimated by non-destructive instrumental neutron activation analysis. The problems in determining Cu were discussed.     

Chemical characterization of graphite by instrumental neutron activation analysis

Nuclear and commercial grade graphite samples were analysed by instrumental neutron activation analysis (INAA) using high flux reactor neutrons. Eleven elements (Na, K, As, Sc, Fe, Cr, Co, Zn, La, Ce, and Sm) were determined in eight samples of graphite (two nuclear grade and six commercial grade) by irradiating at a neutron flux of 3?×?10¹³ cm^?2 s^?1 in CIRUS reactor and assaying the activity by high-resolution gamma ray spectrometry using 40% relative efficiency HPGe detector coupled to an MCA. Concentrations of elements were determined by relative method of INAA. Results of both types of graphites as well as detection limits achieved by INAA method are discussed in the paper.     

Determination of photopeak energy in instrumental neutron activation analysis

The precision and accuracy of the peak energy allocation in γ-ray spectrometry govern the subsequent computer processing of the data. By applying the main procedures for peak energy determination to a well-defined case, it is possible to define the minimal statistical uncertainties to be expected. The systematic bias of the energies obtained is caused mainly by changes in the total count rate. A correction can be applied based on the pulser peak. From the precision and the accuracy of the peak energy determination, the scanning width for automatic peak indexing follows.     

Overall instrumental thermal neutron activation analysis of high-purity materials

A more or less routine method for the determination of up to 55 trace elements down to the ppb range is described. To obtain this, irradiation in a high thermal neutron flux, followed by Ge(Li) γ-spectrometry with large detectors and off-line computerized evaluation of the spectra, is necessary. To cover the range of halflives of the nuclides formed, spectrum measurements are carried out about one hour, one day, one week and one month after irradiation. Only in the case of highly active and rather long-living matrices is chemical separation of the matrix from all impurities necessary. The computer program is written in ALGOL-60.     

Application of anti-Compton counting in instrumental neutron activation analysis

The inherent advantage of anti-coincidence counting of low-level radioactivity is defined in terms of changes in the limits of decision, detection and determination. It appears that the advantage factor can be expressed in the experimentally observed reductions of peak area, compton continuum and natural background. For an array equipped with a sample changer the advantage factor for interference by the compton continuum is4, while that for interference by the natural background amounts to 3. By sacrificing the sample changer and closing its gap with a Nal-plug, additional factors of 1.5 and 2 can be obtained for compton and natural background respectively.     

Multielement determination in water by instrumental neutron activation analysis

Instrumental neutron activation analysis /INAA/ technique has been applied to a water sample to determine the elemental concentrations. The sample was irradiated with a neutron flux of 1.2×10¹² n cm^–2 s^–1 for two different periods followed by counting at three different decay times, using two coaxial type high-resolution Ge/Li/ detectors. The dominant elements determined in the water sample are Ca, Cl, Na, Mg, and K present in ppm-level while Co, I, Mn, Sm, and Sb are present in smaller amounts, approximately on the average 0.01 ppm. Only traces of other elements such as the rare-earth elements, Ag, As, Ba, Cu, Cd, Fe, Sr, W, Zn, seem to be present in the water sample.     

Multielement analysis by sequential instrumental and radiochemical neutron activation

We measured 37 elements in six USGS geological camples and one NBS biological orchard leaf (OL) sample, using sequential INAA and radiochemical group separation coupled with high resolution, high efficiency Ge(Li), and a Ge(Li) with anticoincidence shields. The elemental concentrations in these samples vary over three orders of magnitude. Our results agree very well with the reported values. The rare earth values in PCC-1 are 2–4 times lower than the reported values. Precise REE patterns are defined in USGS samples, which are characteristic of the total rock types. The REE pattern in OL is identical to the mineral apatite. In addition to the possibility that OL may be contaminated by local soil, it is also possible that the uptake of REE trace elements by plants from soil is perhaps dominated by accessory mineral such as apatite, or plants take up the REE from bulk soil in a preferential manner as a smooth function of the REE ionic radii.