Estimation of the possibilities of a neutron generator-based source of thermalized neutrons for activation analysis

Characteristics of a source of thermal neutrons based on an evacuated NG-400 neutron generator with the maximum flux (Φ_f) 2 × 10¹¹ neutron/s for 14 MeV neutrons and 2 × 10⁹ neutrons/s for 3 meV neutrons have been investigated. The possibilities of its application for neutron activation analysis have been estimated. The distribution, composition, and density (φ_T) values of the thermal neutron flux have been measured in the inner cavity of the moderator using activation detectors. φ_T was 2 × 10⁸ and 2 × 10⁶ neutrons/cm² s for thermalized neutrons with energies of 14 and 3 MeV, respectively. The possibilities of the apparatus have been estimated theoretically and experimentally for the cases of thermalized neutrons of 14 MeV and 3 MeV.     

Rare-earth elemental analysis of banded iron-formations by instrumental neutron activation analysis

Representative banded iron-formations (BIFs) from various locations of the eastern Indian geological belt were investigated by instrumental neutron activation analysis (INAA). After pre-concentration, irradiation was carried out using a neutron flux of 5.1·10¹⁶ m⁻²·s⁻¹, 1.0·10¹⁵ m⁻²·s⁻¹ and 3.7·10¹⁵ m⁻²s⁻¹, with thermal, epi-thermal and fast neutrons, respectively. The activities in these samples were measured by a HPGe detector. Ten rare-earth elements, such as La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu, have been qualitatively identified and quantitatively estimated in these samples. The present investigation is an example of employing a pre-concentration method for high iron-containing ores prior to neutron activation analysis.     

Measurement of neutron flux and albedo of water for thermal neutrons with foils of indium in a subcritical nuclear reactor

A subcritical nuclear reactor, Model 9000, Nuclear Chicago, is installed and operating at the Aristotle University of Thessaloniki, in the Atomic and Nuclear Physics Laboratory, at Thessaloniki, Northern Greece. The fuel is about 5500 lbs (2495 kgs) natural uranium metal (U₃U₈), the moderator about 3600 lbs (1633 kgs) light water, H₂O and the reflector is also light, water, H₂O. The lattice core is hexagonal, 42 inches (1.07 m) high and of 35 inches (88.90 cm) maximum diameter. The neutron source at the core is Am-Be 5 curies (185 GBq), 1.1·10⁷n·s⁻¹. The reactor is used for the activation of various materials by neutrons such as indium, the determination of the thermal neutrons flux, the horizontal and the vertical distribution of the neutron flux, material buckling, B, and geometric buckling, B, the parameters of the reactor, and the albedo of water for thermal neutrons with foils of indium. This revised version was published online in July 2006 with corrections to the Cover Date.     

Test-fitting on adsorption isotherms of organic pollutants from waste waters on activated carbon

An alternative method of approach has been developed for the measurement of thermal neutron flux. The method depends only on the activity of the bare foil if the cadmium ratio at the irradiation position is known. The method has been tested on the GHARR-1 facility at the Ghana Atomic Energy Commission using gold and indium foils for the measurement of the thermal neutron flux in the flux range of 10¹⁰–10¹² n·cm⁻²·s⁻¹ and the results compare very well with those obtained using the conventional method (cadmium separation method).     

The determination of fluorine in bones by non-destructive neutron activation analysis using 11.2 sec20F

A fast non-destructive determination of fluorine in bone samples by thermal neutron activation analysis using¹⁹F(n, γ)²⁰F reaction was developed. About 0.1–1 g samples is irradiated for 15 sec in TRIGA MARK II reactor at a thermal neutron flux of 5·10¹¹ n·cm⁻²·sec⁻¹. After 15–25 sec cooling, the 1633 KeV²⁰F activity (T=11.2 sec) is counted for 15 sec with a Ge(Li) spectrometer. A standard sample is prepared by mixing CaF₂ and CaCO₃ powders. The interference from²³Na(n, α)²⁰F is corrected by employing²⁴Na 2754 KeV double escape peak activities in samples and the²⁰F/²⁴Na peak area ratio observed previously for pure Na₂CO₃ powder. The precision is 7% for a bone sample containing 1020 ppm F and the sensitivity is about 10 ppm F.     

A low cost neutron capture prompt gamma-ray analysis facility at a research reactor

A low cost neutron capture prompt gamma activation analysis facility has been constructed at The University of Michigan's Pheonix Memorial Laboratory. Although the neutron beam used has a fairly large epithermal component (Cd ratio 7.1), background levels are low enough to result in satisfactory measurement of over 16 different elements. For the elements of greatest sensitivity (samarium, boron, gadolinium, and cadmium) minimum detectable levels of 3.6·10⁻⁵ to 1.4·10⁻⁵ gram for a one hour measurement are possible. The fast neutrons incident to the detector were found to be minimal. Estimates of up to 3 years of continuous operation before measurable damage is expected.     

A brief introduction to NAA facilities of China Advance Research Reactor at CIAE

China Advance Research Reactor (CARR) at China Institute of Atomic Energy (CIAE), with a non-perturbed maximum thermal neutron flux of 1 × 10¹⁵ cm⁻² s⁻¹ at the center of active area, is one of the most powerful research reactors in the world. Three neutron channels have been allocated for conventional neutron activation analysis (NAA), thermal neutron prompt gamma activation analysis (PGAA) and cold neutron PGAA, respectively. Two irradiation tube systems are installed in the conventional NAA channel. One of them is for short irradiation with the rabbit size of diameter (Φ)19 × 40 mm, the other one is for long irradiation with the rabbit size of Φ39 × 70 mm. The medium temperature is about 45 °C and the thermal neutron flux is about 3 × 10¹⁴ cm⁻² s⁻¹ at sample positions. The flux gradient is expected to be very small according to the designed neutron flux distribution. Pneumatic systems are used for samples transfer. The speed of rabbits is designed to be about 20 m/s, and it takes 3 s to travel from irradiation position to detector. Three sets of gamma counting systems and one delayed neutron counting system are being equipped for routine analysis. They are designed for running continuously and automatically. And all the functions can be operated at laboratory or office through remote controlled computer. Software has been made domestically for spectrum peak search, concentration calculation with relative method and k₀ method with interference corrections and some other functions for the convenience of users.     

Determination of chromium in blood by neutron activation analysis

A procedure for the determination of chromium in blood has been developed with a sensitivity of 5×10⁻³ μg Cr. Dried blood was irradiated with a neutron flux of 10¹² n·cm⁻²·sec⁻¹ in the VVRS reactor for 4 weeks, then the sample was mineralized and the chromium isolated by extraction as perchromic acid. The determination of the chromium content was accomplished by measuring the 0.32 MeV gamma energy of⁵¹Cr. In order to make correction for the interfering reaction⁵⁴Fe(n,α)⁵¹Cr, the formation of chromium from high-purity iron was investigated. The chromium content of the blood samples was between 1.03×10⁻² and 5.2×10⁻² ppm Cr.     

Gamma-ray spectra and sensitivities for 2.8 MeV neutron activation analysis

The use of 2.8 MeV neutrons produced by the D(d, n)³He reaction should be taken into consideration in some applications of radioactivation analysis. The low number of elements activable by these neutrons makes possible to minimize the matrix interference and the background below the characteristic photopeaks. The very low dead-time of the spectrometric measurements permits the use of the maximum neutron flux available now and in the future. The purpose of this paper is to define experimentally the sensitivity of determination for the 16 main elements activable with a 400 keV Van de Graaff accelerator at a 2.8 MeV neutron flux of 2·10⁶ n·cm⁻²·sec⁻¹ on the sample.     

Zirconium as a multi-isotopic flux ratio monitor and a single comparator in reactor-neutron activation analysis

Different methods for the determination of thermal-to-epithermal neutron flux ratio are reviewed and nuclear data for commonly used monitor materials and for Zr isotopes are tabulated. It is shown that the use of the⁹⁴Zr−⁹⁶Zr isotope pair gives significant improvement in precision while measuring Φ_th/Φ_e ratios in the 20<Φ_th/Φ_e<200 range. When the single comparator method is applied, the use of the⁹⁴Zr isotope is suggested as a comparator with the⁹⁴Zr−⁹⁶Zr isotope pair for simultaneous flux ratio determination. Theoretical calculations show that the Zr comparator-flux ratio monitor gives better precision and accuracy than does Ru for two-thirds of the isotopes used for analysis in well thermalized (Φ_th/Φ_e>100) channels. The I_o/σ_th-values for the mentioned Zr isotopes have been experimentally determined and compared with previously published data. Research associate of NFWO.     

Determination of trace impurities in tin by neutron activation analysis

Two methods are described to determine indium and managenese in high-purity tin. In the first method indium and manganese are separated from the tin and antimony matrix activities on Dowex 1X8 anion exchanger. Tin and antimony are adsorbed in 10M HF while indium and manganese are eluted. In the second method the incident γ-ray intensity due to the tin matrix is reduced by placing a lead absorber between the sample and the detector. The reproducibility and the sensitivity of both methods are of the order of 10 ppb for manganese and of 1 ppb for indium for 1 g samples and a neutron flux of 10¹¹ n·cm⁻²·sec⁻¹. Aspirant of the N. F. W. O.     

Design and construction of a facility for neutron activation analysis using the 14 MeV neutron generator at HMS Sultan

The potential for using a small, sealed tube, DT neutron generator for neutron activation analysis has been well documented but not well demonstrated, except for 14 MeV activation analysis. This paper describes the design, construction and characterization of a neutron irradiation facility incorporating a small sealed tube DT neutron generator producing 14 MeV neutrons with fluence rates of 2·10⁸ s⁻¹ in 4π (steady state) and 10¹¹ s⁻¹ in 4π (pulsed). Monte Carlo modeling using MCNP4c and McBend9 has been used to optimize the design of this facility, including the location of a thermal irradiation facility for conventional neutron activation analysis. A significant factor in designing the facility has been the requirement to conform with Ionising Radiation Regulations and the design has been optimized to keep potential radiation doses to less that 1 μSv/h at the external walls of the facility. Activation of gold foils has been used for flux characterization and the experimental results agree well with the modeling.     

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.     

Determination of isotopic composition of lithium by neutron activation analysis; comparison with mass spectrometry

An activation analysis method is described for routine determination of⁶Li-abundances in various lithium compounds on the basis of the reaction sequence⁶Li(n,α)T and¹⁶O(t, n)¹⁸F and the measurement of¹⁸F. Irradiations of diluted equeous solutions of samples containing CrO₃ as internal flux monitor were carried out at a thermal neutron flux density of ϕ≤10¹¹ n·cm⁻²·sec⁻¹. Interferences from variations in neutron self-shielding oxygen concentration and triton range do not exceed 0.5% when using the dilution technique. The results for⁶Li abundances from 3.52 to 7.60% with standard deviations of 1 to 2.5% were confirmed by mass spectrometric measurements.     

Determination of metals in alloys by neutron capture gamma-ray spectrometry

A collimated neutron beam capable of providing a thermal neutron flux of 4.75·10⁷ n·cm⁻²·sec⁻¹ has been used to analyze alloy samples of 1–5 g during relatively short irradiation times of 30 min by the use of neutron capture gamma-ray spectrometry. The analyses were performed by using a mathematical treatment that relates the count ratio of every constituent present in the matrix with the concentration and thus it requires no standards. The technique was applied to the analysis of steel and gold alloy samples. Errors ranged from 0.8%–10%.     

Reagent-loaded and unloaded polyurethane foam as preconcentration matrix in neutron activation analysis

Loaded and unloaded polyurethane foams were examined as a preconcentration matrix in combination with neutron activation analysis. The structure of the foamed polymer is not damaged by short irradiation periods. However the foam skeleton degraded after irradiations for one hour or longer in a neutron flux of 3·10¹³ n ·cm⁻²·s⁻¹. The presence of tin as a major impurity in the polyether-type foam has been detected. This may affect the sensitivity of determination of the relatively short lived isotopes of the elements collected on the foam. On the other hand the polyester-type foam was found to contain only very low amounts of tin. Antimony, indium, gold and mercury collected on the foams were determined with reasonable accuracy.     

In vivo neutron activation analysis of rats

A method of estimating total body calcium and sodium in rats by in vivo neutron activation analysis is described. The subjects were exposed to an integrated flux of about 1.6·10¹¹ thermal neutrons and activity was determined by counting with a 3″×3″ NaI(Tl) detector. The growth of the subjects was followed for about 75 days. The values of total body concentrations obtained are 0.83–0.90% for Ca and 0.128% for Na. Consideration is given to the accuracy attainable and to the effects on the blood and the hematopoietic tissues of the radiation doses imparted.     

Determination of noble metals by resonance neutron activation technique

Rhodium, palladium, platinum and iridium have been determined in silver matrix by nondestructive activation analysis upon activation with cadmium- and silver-filtered resonance neutrons. Experiments with different types of filter combinations are reported. The sensitivity of the method is 5·10⁻³% for rhodium, 5·10⁻³% for palladium, 3·10⁻²% for platinum and 5·10⁻³% for iridium.     

Alternative chromatographic processes for no-carrier added 177Lu radioisotope separation Part I. Multi-column chromatographic process for clinically applicable

The conventional multi-column solid phase extraction (SPE) chromatography technique using di-(2-ethylhexyl)orthophosphoric acid (HDEHP) impregnated OASIS-HLB sorbent based SPE resins (OASIS-HDEHP) was developed for the separation of no-carrier added (n.c.a) ¹⁷⁷Lu from the bulk quantity of ytterbium target. This technique exploited the large variation of lutetium metal ion distribution coefficients in the varying acidity of the HCl solution-OASIS-HDEHP resin systems for the consecutive loading-eluting cycles performed on different columns. The production batches of several hundred mCi n.c.a ¹⁷⁷Lu radioisotope separated from 50 mg Yb target activated in a nuclear reactor of medium neutron flux (Φ = 5·10¹³ n·cm⁻²·s⁻¹) were successfully performed using the above mentioned separation technique. With the target irradiation in a reactor of thermal neutron flux Φ = 2·10¹⁴ n·cm⁻²·s⁻¹ or the parallel run of several separation units, many Ci-s of n.c.a ¹⁷⁷Lu can be profitably produced. The OASIS-HDEHP resin based multi-column SPE chromatography technique makes the separation process simple and economic and offers an automation capability for operation in highly radioactive hazardous environments.     

Thermal neutron activation analysis of hafnium in zircaloy with a Van de Graaff accelerator

Thermal neutron activation analysis of hafnium in zircaloy was investigated with a Van de Graaff accelerator. Thermal neutrons were obtained by moderating Be−D fast neutrons with paraffin blocks.^179mHf isotope with a half-life of 18.6 s, produced by¹⁷⁸Hf(n, γ)^179mHf reaction, was utilized in the present analysis. This method made it possible to analyze hafnium rapidly and non-destructively by using scandium as an internal standard material. Several tens to hundreds of ppm of hafnium in zircaloy samples were determined within 2 minutes with a precision of about ±1%.