Neutron activation analysis calibration

Selected ion monitoring can be used for the determination of the relative amount of each component of a mixture, introduced into the mass spectrometer by the direct inlet probe However, such a determination requires reference mixtures of known composition for calibration. In the present experiment, since the monochloro pentaziridino derivative had not yet been isolated in the pure form, it was necessary to determine its concentration, by an auxiliary method, in a sample which could then be utilized as a reference mixture for further experiments. In order to do this we titrated chlorine in the toxic sample of MYKO 63 (B) by the classical method. The results indicated that the amount of N3P3AZJCI was between 0.5-1.5 %. The large statistical error is due to the low chlorine content in the sample examined. Thus, we used the remarkable possibilities provided by neutron activation analysis when the impurity to be quantified is a chlorinated moiety. It is well-known indeed that the C1 -f 2n peak is amongst the most easily detectable by neutron... 

Cadmium in acidified aqueous solution may be analyzed at trace levels by various instrumental techniques such as flame and furnace atomic absorption, and ICP emission spectrophotometry. Cadmium in solid matrices is extracted into aqueous phase by digestion with nitric acid prior to analysis. A much lower detection level may be obtained by ICP-mass spectrometry. Other instrumental techniques to analyze this metal include neutron activation analysis and anodic stripping voltammetry. Cadmium also may be measured in aqueous matrices by colorimetry. Cadmium ions react with dithizone to form a pink-red color that can be extracted with chloroform. The absorbance of the solution is measured by a spectrophotometer and the concentration is determined from a standard calibration curve (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). The metal in the solid phase may be determined nondestructively by x-ray fluorescence or diffraction techniques. 

FT-IR has been used to determine residual catalyst support in commercial polyethylene at the level of 100 parts per million 841. The method is based on the use of the 1118 or 470 cm-1 bands to determine the quantity of silica support dispersed in the polymer. The band at 2020 cm-1 was used as an internal standard for the amount of polyethylene. Neutron activation analysis was used to calibrate the weight percent of silica present in each polymer sample. 

Silver evaporations were done in the same preparation chamber using an inhouse-constructed evaporation assembly containing a resistively heated tungsten basket. Ag coverages were controlled by a quartz crystal thickness monitor. The deposition rates were typically 0.01 to 0.1 A/s depending on the desired coverage. Coverages were subsequently calibrated by XPS analysis of the Ag 3d and polymer core level (C Is and O Is) intensities as compared to known standards, and by neutron activation analysis (111. 

Even in relatively large programs, few laboratories will justify the initial expense and calibration effort required for development of the emission spectrographic method. As reported by Scott etal. [3], sample preparation will generally not differ significantly from that required for AAS. Instrumental neutron activation analysis (INAA) is only attractive where a reactor is already available, and multielement analysis by this technique requires the use of high resolution Ge(Li) crystals and multiple irradiations for elements with differing activation product half-lives. The key elements, cadmium, nickel and lead still require analysis by AAS because of limitations of the INAA method [4]. 

Simple procedures that require only a dilution of serum or urine have been reported by Schattenkirchner and Grobenski [95], and by Ward et al. [96]. The former diluted samples of sera 1 + 4 with 0.1% Triton X 100 and urine samples 1 + 9 with 0.01 M HC1 and the latter used a 1 + 9 dilution of serum in water. In both cases calibration was by standard additions to compensate for the considerable matrix interferences. Ward et al. [96] demonstrated an excellent correlation (r = 0.98) between neutron activation analysis (NAA) and ETA—AAS analysis of the total plasma Au and albumin bound Au, which contains up to 90% of the total. There was however, a bias towards higher values (10%) by NAA. This difference did not appear to be pre-atomisation losses during ETA—AAS, the recoveries of added Au ranged from 90—105%, nor over-correction by continuum source background corrector. 

The metal coverage was monitored by Auger spectroscopy (AES) and with a quartz crystal oscillator. These data were calibrated by neutron activation analysis to ensure proper determination of the amount of material deposited. The change in frequency of the quartz oscillator was proportional to the film thickness. 

Lithium metabolism and transport cannot be studied directly, because the lack of useful radioisotopes has limited the metabolic information available. Lithium has five isotopes, three of which have extremely short half lives (0.8,0.2, 10 s). Lithium occurs naturally as a mixture of the two stable isotopes Li (95.58%) and Li (7.42%), which may be determined using Atomic Absorption Spectroscopy, Nuclear Magnetic Resonance Spectroscopy, or Neutron Activation analysis. Under normal circumstances it is impossible to identify isotopes by using AAS, because the spectral resolution of the spectrometer is inadequate. We have previously reported the use of ISAAS in the determination of lithium pharmacokinetics. Briefly, the shift in the spectrum from Li to Li is 0.015 nm which is identical to the separation of the two lines of the spectrum. Thus, the spectrum of natural lithium is a triplet. By measuring the light absorbed from hollow cathode lamps of each lithium isotope, a series of calibration curves is constructed, and the proportion of each isotope in the sample is determined by solution of the appropriate exponential equation. By using a dual-channel atomic absorption spectrometer, the two isotopes may be determined simultaneously. - ... 

Neutron activation analysis. (See Chap. 30 in Vol. 3.) Samples are activated inside the reactor. Characteristic radiations given off after (or during) activation are measured. From these measurements one can deduce the elements that are present in the samples and calculate their respective quantities. This analysis is very selective and in many cases shows an extreme sensitivity. Frequently it does not require a chemical sample preparation, thus excluding errors introduced by such procedures. Therefore, neutron activation is frequently used to calibrate or validate other analytical procedures and to detect small traces of elements of specific interest. 

A comparative study of the thorium and uranium content in soil samples by gamma spectrometry and neutron activation analysis (NAA) showed a good correlation between the two methods (Anilkumar et al. 2012). The soil samples were dried, powdered, and packed in 250 mL plastic containers, counted for 50,000 with a p-type coaxial HPGe detector that was calibrated. Based on the assumption that was in equilibrium with its daughters, the intensity of the gamma lines at 352 and 609 keV from Pb and respectively, were used to assay the uranium in the... 

In particular, the neutron activation analyst, to whom efficiency curves may be an irrelevance, is not weU served by most spectrum analysis packages. As far as activation analysis is concerned, there is much evidence to show that absolute analysis, calculating concentrations from first principles, is much less accurate than comparative analysis. Apart from aU of the problems which derive from having to use efficiency calibration curves, there are specific problems associated with defining and measuring neutron fluxes and cross-sections which make absolute analysis not worthwhile, in my opinion (although there are those who have devoted a considerable amount of effort into developing absolute neutron activation analysis procedures who would dispute that). For that reason, almost every activation analysis involves irradiation of samples and standards. A direct comparison between them is the simplest solution. 

Neutron activation analysis. Polymer powder is irradiated with neutrons. Silicon is activated by the reaction Si(N,p) Al. The concentration of silicon is measured by counting the 1.78 MeV gamma - ray emission from the decay of A1. A silicon standard is used for calibration. 

Examples of using reference samples for calibration can be found in several chapters of the uses Methods for Geochemical Analysis (Baedecker 1987). Solid reference sample powders are used in cahbrating the dc arc emission, energy-dispersive X-ray and instrumental neutron activation analyses described, while acid-dissolved rock reference samples are used for IGP emission analyses and fused reference samples are used for wavelength-dispersive X-ray analyses. 

Methods of Abundance Measurement. Mass spectrometry (Table 2) is the common form of analysis for lead isotope abundances. Samples suitable for mass spectrometer calibration are in Table 3. Neutron activation ( ° Pb/ ° Pb) and alpha particle activation ( ° Pb/ Pb and ° Pb/ ° Pb) show promise of getting some data on materials having very low lead contents. 

The classical calibration of NAA methods involves comparison of sample activities with those of co-irradiated standards of the same element. Especially at multi-element analysis, the need for a large number of standards has limited the sample throughput capacity. To circumvent this, alternative calibration techniques have been elaborated. The single comparator method makes multi-element determinations possible, by use of a single element standard (neutron flux monitor). The mass of the analyte is calculated by use of an experimentally determined element-specific factor (k-value), valid for the analytical equipment in question (Girardi et al., 1965 Linekin, 1973 Simonits et al., 1975). Later, a more generalized standardization method, based on accurately determined constants for the active compound nuclei (ko-factors), and applicable to various analytical equipments, has been proposed (Moens et al., 1984 De Code et al., 1987). 

Determination of uranium in soil samples can be carried out by nondestructive analysis (NDA) methods that do not require separation of uranium (needed for alpha spectrometry or TIMS) or even digestion of the soil for analysis by ICPMS, ICPAES, or some other spectroscopic methods. These NDA methods can be divided into passive techniques that utilize the natural radioactive mission (gamma and x-ray) of the uranium and progeny radionuclides or active methods where neutrons or electromagnetic radiation are used to excite the uranium and the resultant emissions (gamma, x-rays, or neutrons) are monitored. In many cases, sample preparation is simpler for these nondestructive methods but the requiranent of a neutron source (from a nuclear reactor in many cases) or a radioactive source (x-ray or gamma) and relatively complex calibration and data interpretation procedures make the use of these techniques competitive only in some applications. In addition, the detection limits are usually inferior to the mass spectrometric techniques and the isotopic composition is not readily obtainable. 

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