Gamma ray spectra and sensitivities for 14 MeV neutron activation analysis

The purpose of this study was to define experimentally the sensitivity of determination for 63 different elements by 14 MeV neutron activation, with a 150 kV Cockroft-Walton accelerator at a neutron flux of 2·10⁸ n·cm⁻²·sec⁻¹ on the sample. The obtained gamma ray spectra are given, and the origin of the photopeaks observed are explained. A maximum irradiation time of five minutes was used as a convenient experimental limit to obtain the maximum sensitivity, considering, however, that the tritium target life is limited, and that the time to perform an analysis has to be reasonable. The practical use of 14 MeV neutron activation analysis is demonstrated by the detection limits obtained.     

Experimental sensitivities for 3 MeV neutron activation analysis

The experimental sensitivity for 72 different elements using 3 MeV neutron activation has been investigated. Using a 200 kV Cockcroft-Walton neutron generator with a 3 MeV neutron flux of about 1.5·10⁶n·cm⁻²·sec⁻¹, γ-ray spectra of 51 elements were obtained with a sufficient number of photopeak counts for sensitivity calculations using a photopeak integration method. A useful table summarizing the sensitivity results is given. That 3 MeV neutron activation analysis is practical, is demonstrated by the experimental sensitivities obtained. Guest worker from the Institute of Nuclear Techniques, Academy of Mining and Metallurgy, Krakow, Poland, at the National Bureau of Standards, 1968–1969.     

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.     

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.     

Fast-neutron activation analysis with short-lived nuclides

At the GKSS Research Center Geesthacht, a new 14 MeV activation facility—a 5·10¹² n/s neutron generator combined with a fast rabbit system (KORONA)—is being installed. Homogeneous neutron flux at a level of 5·10¹⁰ n·cm⁻²·s⁻¹ and sample transfer times of 140 ms to a 16m distant detector station are characteristic features of the facility described in the paper. With special consideration of short-lived nuclides and including cyclic activation, the analytical prospects with the intense neutron source are discussed, and sensitivities for 78 elements are presented.     

Gallium determination in biological samples

A sensitive, simple and time-saving method has been developed for the neutron activation analysis of gallium at concentrations around 10⁻⁴ ppm in biological tissues. After a 24-hour irradiation in a thermal neutron flux of 2.8·10¹³ n·cm⁻²·s⁻¹ and a purification by ion-exchange chromatography to eliminate troublesome elements such as sodium, iron and copper, the⁷²Ga activity is measured with enough accuracy for the method to be applicable in animal physiology and clinical toxicology.     

Etude de quelques reactions nucleaires induites par les neutrons rapides de pile

Conclusion Dans une première partie, l’étude des réactions engendrées par les neutrons rapides de pile sur douze éléments a montré que certaines de celles-ci pouvaient être utilisées pour un dosage quantitatif. Dans une seconde partie, nous proposons un dosage radiochimique du silicium par la réaction²⁸Si(n, p)²⁸Al qui a, dans nos conditions de travail, sa limite de détermination à 620 μg. A titre de comparaison, signalons que cette limite se situe par irradiation avec des neutrons de 14 MeV, produits au moyen d’un accélérateur (flux de 5·10⁸ n·cm⁻²·sec⁻¹), à environ 10 μg. Le dosage non destructif du silicium dans le diméthylpolysilane est décrit.

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In the first part, the fast-neutron flux available in reactor cores was utilized to define experimentally the sensitivity for the determination of 12 different elements, based on fast-neutron nuclear reactions. The fluxes available with our AGN-201 P reactor are in the range of 10⁹–10¹⁰ n·cm⁻²·sec⁻¹ in the 1–4 MeV region. A good sensitivity was obtained for²⁷Al,⁵²Cr,⁵⁶Fe,²⁸Si,²³Na [by (n, p) reaction],²⁷Al,³¹P,⁸⁹Y [by (n, α) reaction] and¹⁹⁷Au,¹⁸³W,⁸⁹Y [by (n, n′) reaction]; the elements Cl, Ca, Pb failed to give reactions. In the second part, a non-destructive method for the determination of silicium based on the reaction²⁸Si(n, p)²⁸Al is proposed. The limit of determination is about 0.6 mg for a neutron flux of 10⁹ n·cm⁻²·sec⁻¹. As an example, Si in dimethylpolysilane was determined.

     

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.     

Fluorine analysis by activation with an isotopic fast-neutron source and counting Nitrogen-16

A rapid, nondestructive method has been developed for determination of fluorine by activation with fast neutrons from a²⁴¹Am-²⁴²Cm-Be source and counting the 6–7 MeV γ rays of the product nitrogen-16. The total neutron output of the source is 4.8·10⁹ unmoderated neutrons per second and the flux is 1.4·10⁸ fast n·cm⁻²· sec⁻¹. The γ-ray detectors consist of two opposing, matched cylindrical NaI(Tl) crystals 10 cm long and 10 cm in diameter. The sample is irradiated for 30 seconds, cooled for 4 seconds, and then counted for 30 seconds. The sensitivity is 4.8·10⁴ counts nitrogen-16 per gram fluorine, and the limit of detection is 0.4 mg fluorine in a 10-gram sample. A reproducibility of 0.24% is achieved. The relative standard deviation of the specific count rate of nitrogen-16 for 11 fluorine compounds is 1.31%.     

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.     

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.     

Activation analysis with cyclotron-produced fast neutrons. Application to instrumental multi-element analysis and to the radiochemical determination of fluorine

Fast neutrons produced by irradiation of a thick beryllium target with 20–50 MeV deuterons are used for activation analysis. The spatial neutron flux distribution around the target is measured. A rotating sample holder is used for the simultaneous irradiation of samples and standards. Instrumental analysis can be applied for a number of elements. As an example, results for calcium and strontium in some reference materials are given. The¹⁹F(n, 2n)¹⁸F reaction is used for the radiochemical determination of fluorine in rocks with a fluorine concentration ranging from 9 to 5400 μg·g⁻¹ Aspirant of the N.F.W.O.     

Analytical use of neutron-capture gamma-rays

Certain elements which are not possible to detect with conventional neutron activation analysis can be measured using thermal neutron-capture gamma-ray analysis. The use of a curved neutron guide at the High Flux Reactor, Grenoble, with a thermal neutron flux of 1.5·10¹⁰n·cm⁻²·sec⁻¹ and the advantage of a low-background counting system (Ge(Li) detector) far from the reactor core are described. Experimental detection limits of a number of elements are given for the low-energy and the high-energy regions. Some applications of the capture gamma-ray method in the whole energy range are studied and are briefly discussed.     

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.     

Evaluation of stray neutron distribution in medical cyclotron vault room by neutron activation analysis approach

Stray neutron distribution in a medical cyclotron vault room was evaluated by neutron activation analysis (NAA). Neutrons were generated in the production of radioactive nuclides, such as ¹⁸F, ¹¹C, ¹³N and ¹⁵O, for diagnostic usage. Indium foil was adopted to evaluate the stray fast and thermal neutron intensity based on ¹¹⁵In(n_f, n′)^115mIn and ¹¹⁵In(n_th, γ)^116m1In reactions, respectively. The indium foils were weighed, sealed and placed at 62 points around the 6.7×8.2 m² cyclotron room. Additionally, each indium foil was exposed for over 80 minutes during cyclotron operation and γ-peaks were analyzed using an HPGe detector to evaluate the number of stray fast (Φ _f) or thermal (Φ _th) neutrons. The minimum to maximum numbers of fast and thermal neutrons were (3.47±0.11)×10³ to (1.06±0.21)×10⁴ n·cm⁻²·s⁻¹ and 9 to 965 n·cm⁻²·s⁻¹, respectively. The minimum detectable limit for stray neutrons was included herein to demonstrate the reliability. Accordingly, 60 and two points, respectively, the confidence level associated with the reported intensities of fast and thermal neutrons reached 95%. The low qualified ratio in the evaluation of stray thermal neutrons might have been caused by either the high Compton scattering plateau or the low intensity of the gamma-ray peak in the relevant spectrum.     

The determination of carbon,nitrogen and oxygen in gases by neutron time-of-flight spectrometry

Carbon, nitrogen and oxygen were determined in gases by time-of-flight spectrometry of prompt neutrons from the respective reactions¹²C(d, n)¹³N,¹⁴N(d, n)¹⁵O and¹⁶O(d, n)¹⁷F, produced by a pulsed beam of deuterons of 2 MeV (for nitrogen) or 3 MeV. The analysis is non-destructive and requires about 15 min. per sample. The relative standard deviation for all three elements was about ±3%. Detection limits, using a total irradiation current of 20 millicoulombs, for carbon, nitrogen and oxygen, respectively, were 6·10⁻⁸ g, 2·10⁻⁷ g and 1.7·10⁻⁷ g per cm² cross-sectional area of irradiating beam.     

Neutron activation analysis of rare earth impurities in metallic uranium

A method with a sensitivity of 2·10⁻⁷ to 1·10⁻¹⁰% has been developed for determining Yb, Ho, Dy, Gd, Eu, Sm and La impurities in metallic uranium by means of neutron activation. The method is based on a preliminary chromatographic separation of the total amount of rare earth elements from uranium by passing the solution in sulphuric acid through KU-2 cation exchange resin and eluting the traces of uranium retained by the resin with a solution of ascorbic acid. The rare earth impurities are then eluted from the resin with 4–5N HCl, evaporated, and irradiated for 20 hours with a neutron flux of 1.2·10¹³ n·cm⁻²·sec⁻¹. Subsequently the traces of the rare earth elements are co-precipitated with Fe(OH)₃, dissolved in concentrated HCl and separated from the iron and other impurities by passing the solution through Dowex 1X8 anion exchange resin in the chloride form. The individual rare earth elements are then separated from each other using KU-2 cation exchange resin and a solution of ammonium α-hydroxyisobutyrate as the eluant.     

Performance comparison of 2.8 MeV and <Superscript>241</Superscript>Am-Be neutrons based moisture measurement setups

Performance of a ²⁴¹Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation. In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an ²⁴¹Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8 MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture setup.     

Radiochemical determination of chromium in biological tissues by ion-exchange

A simple ion exchange procedure has been developed for the separation of chromium from the other chemical elements in biological tissues. This procedure combined with neutron activation analysis has been applied successfully to the determination of chromium in a reference biological material. The precision was ±11%, the accuracy 3% and the sensitivity found was 10 ng with only 20 hrs irradiation at 2.8·10¹³ n·cm⁻²·sec⁻¹ flux The main steps of the procedure are: wetdigestion of the irradiated tissue, oxidation to chromium (VI), fixation onto an anion resin in sulfate form, washing of the resin with 1N H₂SO₄, collection of chromium by reductive elution for counting and finally determination of the chemical yield by reactivation.