Precision in 14 MeV neutron activation analysis

The errors of analysis due to the different parameters involved in 14 MeV neutron activation analysis method are studied. Formulae to calculate these erros have been developed when possible. Otherwise they have been evaluated for special experimental situations. Special cases where some parameters become critical, as far as precision is concerned, have been mentioned.     

Sulfur determination in coal by 14 MeV neutron activation analysis

A procedure involving the irradiation of coal samples with 14 MeV neutrons and subsequent gamma-ray spectrometry of the irradiated sample for the estimation of solfur in coal, has been outlined. The samples were irradiated with 14MeV neutrons from a Cockroft-Walton type generator for one minute and then subjected to gamma-ray spectrometry for another minute using an automated transfer cyclic system. Ten such cycles were repeated for accumulating events under the 2130 keV gamma ray photopeak belonging to³⁴P (T=12.4 s) produced by the³⁴S(n, p)³⁴P reaction for assessing the lower level of detection, LLD, of Sulfur. Interferences due to the presence of other elements in coal were also determined. Sulfur can be determined at LLD of 0.25% in coal provided a 5 g sample of the coal is irradiated with a neutron flux of 5·10⁹ n·cm⁻²·sec⁻¹ assayed with a gamma ray spectrometer having a large hollow core Ge(Li) detector and an anti-Compton shield.     

Geometry errors in 14 MeV neutron activation analysis

The effects of inaccurate sample sizes and sample positioning on 14 MeV neutron activation analysis results are estimated for 30, 20 and 10 mm diameter targets. It appears that axial positioning is the most critical parameter and that using a larger tritium target will yield an overall improvement of the reproducibility. Aspirant of the N.F.W.O.     

14 MeV neutron activation analysis of gold jewellery

Samples of nominal 18 carat and 21 carat gold jewelleries from the local market were non-destructively bulk analyzed using neutron activation analysis. Neutrons of 14 MeV energy were used with a fast pneumatic sample transfer system. The actual gold contents, as well as the composition of the base metals in these samples were determined. The fast neutron activation was found to be an efficient, quick and accurate method of characterizing the precious metal objects routinely in bulk, with a large sample throughput. The results demonstrate the commercial availability of the technique for non-destructive bulk analysis of precious metal objects.     

Multielement analysis of a Milanese air-dust sample by 14 MeV neutron activation

The 14 MeV neutron activation technique is illustrated for multi-element analysis of a Milanese air dust sample. The neutron generator and electronic system, the efficiency and flux calibration, the -ray background, the sample preparation and the peak analysis used are described. After careful corrections of all possible interferences and error calculations, the results of 23 elemental concentrations are compared with those of other analytical techniques in the scope of an interlaboratory test.     

Determination of potassium in beet by 14 MeV neutron activation analysis

The applicability of 14 MeV neutron activation analysis for the determination of K in beet has been investigated by measuring the 2.167 MeV gamma-line from the decay of³⁸gK produced in the³⁹K(n, 2n) reaction. Beet samples were treated in different solutions of KCl and HgCl₂ to study the diffusion of K⁺ ions into the beet cells. The contribution of the gamma-line to the measured peak area from³⁸Cl produced in the³⁷Cl(n, γ) reaction was found to be 1%. Results obtained by fast neutron activation analysis and by flame spectrometry have been compared, and good agreements were found.     

Determination of silicon in aluminium by 14 MeV neutron activation analysis

A method has been developed for determining silicon in aluminium by fast neutron activation. It is based on the separation of two gamma lines by a Ge(Li) detector: the 1.73 MeV line from the product of²⁷Al(n, α)²⁴Na and the 1.78 MeV line from the²⁸Si(n, p)²⁸Al reaction. In the case of aluminium-silicon alloys 100 μg silicon can be determined, with an error of 10% in an aluminium sample of 1 g. This work was supported in part by the International Atomic Energy Agency.     

Silicon determination in mine flue-dust by 14 MeV neutron activation analysis

The Si-contents of flue-dust and sedimented dust from Czechoslovak mines were determined by instrumental activation analysis with 14 MeV neutrons using a flux of 10⁷ cm⁻²·s⁻¹. The amounts determined range from 3 to 30 mg.     

14 MeV neutron activation analysis using short-lived products

Cyclic activation using pneumatic shuttling system and switch off and on the neutron source and detector are described in order to eliminate some uncertainties by the provision of more accurate timing, the measurement of the effective activating neutron flux and the correction for the detection system dead time.     

Calculated screening effect in 14 MeV neutron activation analysis

The screening effect produced by a sample upon a standard located behind it is calculated. Curves for the secreening effect as a function of the sample material and of the sample depth are given.     

Utilization of characteristic X-rays in 14 MeV neutron activation analysis

The possibility of the use of characteristic X-rays, emitted after IT of EC type of radioactive decay, for analytical purposes in 14 MeV neutron activation analysis was investigated. Elements from Cr to U were theoretically considered and 24 of them experimentally examined. The results showed usefulness of the technique for several elements in spite of the troublesome selfabsorption effect. It is expected that the 0.1% determination limit can be achieved for the most suitable elements.     

Optimum sample shape for 14 MeV neutron activation analysis

Based on the criteria of the maximum induced activity, the problem of the optimum sample shape was analyzed for a given volume of sample. Its shape was assumed to be cylindrical and the optimum values for the height-to-diameter ratio (presented in the included tables) were calculated under various circumstances. Coaxial and perpendicular sample—target irradiation geometries were considered.     

14 MeV neutron activation analysis applied to a non-aqueous flowing system

The feasibility and advantages of fast neutron activation analysis in a non-aqueous flowing system, using economical irradiation techniques are outlined. The application of the method to the determination in solution of elements producing isotopes with half lives in the range 588—29.4 sec, the selection of the optimum flow rate to minimise interferences for each element, and their limits of detection are also given. A method for the prediction of the optimum flow rate, on a given system, for the determination of any element producing an isotope of known half life is also given.     

14 MeV neutron activation analysis of chicken dung and dates

Simultaneous determination of N, Mg, Al, Si, P, Cl, K, Ca and Fe in chicken dung and dates was carried out using fast neutron activation analysis (FNAA) with a SAMES J25 neutron generator. The activities were measured with a 72 cm³ high purity germanium detector using the relative method. The accuracy was checked with the aid of a standard reference material of milk powder A11 supplied by the IAEA. For the nitrogen contents, the results were compared to those obtained by the classical KJELDAHL method.     

A new technique for the 14 MeV neutron activation analysis of sodium and potassium

Cerenkov radiation produced in perspex by β and γ emitters may be readily measured by counting in the tritium channel of a liquid scintillation spectrometer, a technique which has interesting applications in neutron activation analysis. Further the fact that there are often considerable variations in the β energies of different radionuclides produced by activation means that by the use of suitable absorbers the determination of isotopes in a mixture is frequently possible. Such a method has been applied in the determination of a mixture of sodium and potassium. At the same time sensitivities and detection limits of the other alkali elements have been investigated and compared with results obtained from conventional gamma spectral analysis. Using such a technique it has proved possible to effect a considerable increase in sensitivity for the determination of sodium and potassium.     

The application of cherenkov counting in 14 MeV neutron activation analysis

The conventional method of measurement in 14 MeV activation analysis is to employ gamma-ray spectrometry. The method has the advantage of good selectivity but this is at the expense of sensitivity. In order to improve sensitivity the authors have employed Cerenkov counting techniques and by the careful use of absorbers in a specially designed cell together with double decay procedures have still retained a considerable degree of selectivity. The method has been applied to neutron flux measurement and to the majority of the elements in the periodic table.     

Computer simulaion of gamma spectra in 14 MeV neutron activation analysis

The method of simulation of gamma-spectra based on the experimental library spectra of particular radioisotopes is described. The library spectra were obtained by activation of pure element sample with the use of a 14 MeV neutron generator, counting them with a NaI(T1) scintillation spectrometer and decomposing of mixed spectra to spectra of separate radioisotopes. The simulated and measured spectra of an artificial sample are compared.     

Characterization of InxGa1−xAs crystals by 14 MeV neutron activation analysis

Indium doped GaAs crystals are analyzed quantitatively for indium by non-destructive 14 MeV neutron activation analysis. Experimental conditions are optimized to provide a precision of ±5% and a practical sensitivity of 50 ppm, by weight. The accuracy of the neutron activation method is established by comparison with the results obtained by atomic absorption and Rutherford back-scattering techniques. The method has been applied for determining the homogeneity of indium distribution of wafers by sectional analysis and is demonstrated as a reference method for calibrating the low temperature photoluminescence technique.     

The determination of oxygen and silicon in diamond by 14 MeV neutron activation analysis

Techniques for the measurement of low levels of oxygen and silicon, using fast neutron activation analysis, have been developed and applied to high-quality diamonds. For oxygen, a limit of detection of approximately 5 μg has been established. Sources of error have been studied and eliminated, the ubiquitous occurrence of oxygen being the major problem. Within the accuracy of this work, the results obtained show no significant differences in the oxygen contents of diamonds of different types, or of diamonds from different sources. An oxygen content of 35±4 ppm has been established for high-quality colourless diamonds. For silicon, a limit of detection of 25 μg was established and the average silicon content of these diamonds was found to be less than 3 ppm. It is concluded that the oxygen in high-purity diamonds is present as CO₂ or H₂O and not in silicate inclusions.     

Rapid determination of molar ratios in binary systems by 14 MeV neutron activation analysis

The magnetic characteristics of barium ferrite, a compound widely used for magnetic materials, depend on the molar ratio of iron(III) oxide to barium oxide. On account of this fact, activation analysis using 14 MeV neutrons was applied for the rapid and non-destructive determination of the molar ratio of iron(III) oxide to barium oxide in barium ferrite. Iron was detected as⁵⁶Mn produced from the⁵⁶Fe(n, p)⁵⁶Mn reaction, and barium as^137mBa originating from the¹³⁸Ba(n, 2n)^137mBa reaction. A linear relation was obtained between the ratio of counts of⁵⁶Mn and^137mBa and the molar ratio of iron(III) oxide to barium oxide; the corrected gradient of the experimental calibration curve, obtained with^137mBa internal standard, agreed well with the calculated value. The molar ratios of iron(III) oxide to barium oxide obtained by activation analysis and by chemical analysis were in good agreement.