Investigation of groundwater flow with the aid of indium—EDTA-complex using neutron activation for the determination of the tracer

Indium-EDTA-tracer detected in water samples by neutron activation analysis was used in a multitracer karst experiment carried out in the catchment area of Ljubljanica springs (Yugoslavia) in 1975. For this purpose it was tried, to develop the detection procedure in such a manner, that the samples could be processed with reduced labour demand and reduced interferences by water ingredients. This was attained by liberating the indium from the EDTA-complex and subsequent coprecipitation on bismuth-hydroxide which yields no interfering γ-emitters under irradiation with reactor neutrons. Flow parameters in the Ljubljanica karst system were measured and are presented.     

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.     

Neutron energy spectrum determination and flux measurement using MAXED, GRAVEL, and MCNP for RACE experiments

Stainless steel flux wires were used to determine the neutron energy spectra and total flux during the Reactor Accelerator Coupling Experiments (RACE) at The University of Texas at Austin. A LINAC electron accelerator produced 20 MeV electrons at a power of 1.6 kW, which struck a tungsten-copper target to produce bremsstrahlung radiation and photoneutrons. The neutrons produced in the target were multiplied by the subcritical core of a Triga reactor. The purpose of the RACE experiments is to develop a sub-critical accelerator driven system that would be capable of transmuting actinides from spent fuel. Flux measurements were made with 1.58 mm diameter stainless steel wires placed throughout the core between the fuel rods and cadmium covered and uncovered gold and indium foils above the target. The MAXED and GRAVEL computer codes were used to perform the spectrum unfolding. The composition of the stainless steel wires was determined using neutron activation analysis with comparators prior to the flux measurement. The reactions measured in the stainless steel to determine the flux were ⁵⁰Cr(n,γ)⁵¹Cr, ⁵⁸Ni(n,p)⁵⁸Co, ⁵⁴Fe(n,p)⁵⁴Mn, and ⁵⁸Fe(n,γ)⁵⁹Fe. Flux measurements agreed well with an MCNP simulation of the experiment.     

Contribution a l'etude du dosage par radioactivation du sourfre et du phosphore en tres faibles concentrations dans les metaux de tres haute purete (Aluminium,magnesium, cuivre,fer, nickel)

The chemical separation of sulphur and phosphorus from pure iron and nickel, is described. Sulphur has been determined first by irradiation in fast neutrons, then by irradiation in mixed fast and thermal neutrons. The two methods gave two different results; so, we were led to point out the same phenomenon asJ. Le Hericy had already pointed out for the determination of sulphur in copper. We found that the abnormal amounts of sulphur came from external contamination with chlorine since sulphur is then produced by the³⁵Cl(n, p)³⁵S reaction. The diffusion of³⁵S atoms (produced on the edge of the samples) explains that the concentration of sulphur decreases from the edge to the middle of the sample. We prepared samples of iron and nickel, artificially covered with ammonium chloride, and we studied the apparent concentration of sulphur as a function of the depth in these samples. Our experiences pointed out that the contamination in sulphur yielded by the (n, p) reaction, reaches very quickly the middle of the samples. This phenomenon limits the determination of sulphur by the³⁴S(n, γ)³⁵S reaction, in nickel and iron.      

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%.     

Non-destructive determination of uranium and thorium in geological materials by resonance-neutron activation analysis

A simple method is described for the determination of uranium and thorium in gological materials. The samples are irradiated in a reactor with resonance and fast neutrons behind a cadmium filter. Compared with an irradiation with the whole reactor neutron spectrum, the matrix activities are reduced to about 1%, those of uranium (²³⁹Np) and thorium (²³³Pa) to about only 50 and 25%, respectively. This relative diminution of matrix activities allows the γ-measurement of²³⁹Np and²³³Pa as early as after two days' cooling time; in samples with high uranium contents the determination of²³³Pa requires one month's cooling time. This non-destructive procedure yields a detection limit of 0.1 ppm for uranium and thorium in samples of 200 mg, with an error of ±5%. Dedicated to ProfessorW. Borchert on the occasion of his 60th birthday.     

Determination of lithium and its isotopic composition by activation analysis and measurement of8Li and17N

The non-destructive determination of lithium was performed by using a Cerenkov counter for the detection of the 13 MeV (max) β-particles from the 0.84 sec⁸Li produced by the reaction⁷Li(n,γ)⁸Li. Under optimal conditions for a favorable signal-to-noise ratio, a count rate of about 35 cps/μg lithium at the beginning of the measurement was obtained, with a background of 4.5 cps and a working range of 3–400 μg lithium. The interference of other elements was studied. Several lithium-containing minerals and a sample of Dead Sea water were analyzed. The isotopic composition of lithium in aqueous solutions was determined by the simultaneous measurement of the neutrons produced by the reactions⁶Li(n,α)t and¹⁸O(t,α)¹⁷N, and the β-particles emitted by⁸Li.     

Neutron activation analysis of semiconductor silicon

The determination of impurities in semiconductor silicon by nondestructive and destructive NAA is described. To improve the detection limit, a multiple beta—single gamma detector assembly is used. It is shown that²⁴Na is also produced from silicon by a (n, αp) reaction with reactor neutrons. The cross-section with fission neutrons is 1.8·10⁻⁹ barn.     

Mean squared slowing-down distance and age of americium-beryllium neutrons in perspex

The mean squared slowing-down distance, <r ²>, and the age to themal capture (Migration Area),M ², are direct measures of the slowing-down, and the spreading out, processes of neutrons in a medium. They also enter directly into reactor calculations. These parameters have been determined experimentally for Am-Be neutrons (mean energy 4.46 Me V), in a block of perpex, using the activities induced in thin indium foils from the¹¹⁵In(n,)¹¹⁶In reactions.     

Contribution a l’etude du dosage par radioactivation du soufre et du phosphore en tres faibles concentrations dans les metaux de tres haute purete (Aluminium,magnesium, cuivre,fer, nickel)

The analytical procedure for the determination of sulfur in copper by activation with thermal neutrons is given. The purifications necessary to obtain a radiochemically pure precipitate of baryum sulphate are described. The occurrence of some discrepant values in the determinations led to the observation, for the first time, of abnormally high contents of³⁵S^* at a relatively important depth in the samples of irradiated copper (as deep as about 300 μ). Therefore it is necessary to etch the samples to a depth of 300 μ at least on each surface, before doing the chemical separations. Owing to the great influence of the reaction³⁵Cl(n,p)³⁵S^*, the determination of sulfur by thermal neutrons is only possible at contents higher than 10⁻⁶, even if the chlorine concentration is very low (2·10⁻⁸ Cl introduces a correction in terms of sulfur of the order of 10⁻⁶). For sulfur contents lower than 10⁻⁶, the determination is made by irradiation in fast neutrons. The analytical procedure is described and the corrections in the presence of phosphorus and chlorine are discussed. At contents of the order of 10⁻⁸, the corrections are very small and the determination of some 10⁻⁷ of sulfur is easy. Finally, the determination of phosphorus in copper by activation in thermal neutrons is given. The chemical separations are the same as in the preceding case. Contents of the order of 10⁻⁸ phosphorus are determined without difficulty. The results of the determination of sulfur and phosphorus in many samples of copper are indicated: OFHC copper, High Purity copper (99.999%) and different samples of zone refined copper prepared at the Vitry’s Laboratory.      

Photoneutrons from a beryllium reflector: a potential source of problems with Zr–Au flux monitors in <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript> standardization based neutron activation analysis

The assumption that the shape of the epithermal neutron spectrum can be described, in any research reactor, by the 1/E ^1+α function is a fundamental starting point of the k ₀ standardization. This assumption may be questioned from a reactor physics viewpoint. The type of moderator, the existence of neutron reflectors, the additional production of (γ, n) neutrons and resonance capture by construction materials may be different for each reactor, with consequences for the shape of the neutron spectrum. This dependency may explain that various practitioners reported contradicting experiences with the use of Zr–Au flux monitors for the determination of the α-parameter. An objective view on the influence of the design of the reactor and irradiation facility on the shape of the neutron spectrum can be obtained by modeling. This has been applied in the Reactor Institute Delft for reactor configurations in which the irradiation facilities face the fuel elements with the presence of beryllium reflector elements. The Monte Carlo calculations indicate a distortion of the 1/E ^1+α relationship at the higher energy edge of the epithermal neutron spectrum. This distortion is attributed to the formation and thermalisation of both photoneutrons and (n, 2n) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of ⁹⁵Zr, other than represented by the 1/E ^1+α function. The obtained relationship between neutron flux and neutron energy was also used for estimating the f-value and compared with the value obtained by the Delft Cr–Mo–Au flux monitor.     

Absolute intensity of the 140.5 keV gamma-ray of99Mo

The induced activity of the⁹⁹Mo isotope is mostly determined via the 140.5 keV γ-line, which is the strongest gamma-ray of its daughter,^99mTc. Some recent literature, however, indicates a direct feeding of this energy level from the mother isotope as well. Considering the importance of this line in practice as well as the large controversy and scattering in relevant nuclear data available at present, a combined effort was made to remeasure this questionable absolute intensity. A relative method of irradiating a Mo-target with reactor neutrons and repeatedly measuring its (n,γ) induced activity relative to the 181.1 keV and 739.5 keV gamma lines of⁹⁹Mo as internal references was used. The weighted average of different runs yielded γ(⁹⁹Mo, 140.5 keV)=(5.07±0.37)%. As a consequence, when the 140.5 keV gamma line is used, the contribution from the⁹⁹Mo mother isotope should always be taken into account, e.g. in neutron cross-section measurements and neutron activation analysis.     

Low level Pu and Am estimation in liquid waste from nuclear reactor

Estimation of very low amount up to pico-gram of Am and Pu in the liquid waste of U–Pu fuel cycle of the irradiated U fuel from the nuclear reactor has been carried out using combined method of α- and γ-ray spectrometric techniques. ²⁴¹Am was estimated by γ-ray spectrometry from a plancheted source. In spite of the same α energy of 5.49 MeV for ²⁴¹Am and ²³⁸Pu, the amount ²³⁸Pu was estimated by α spectrometry from the same plancheted source after subtracting amount of the ²⁴¹Am obtained from γ-ray spectrometry. The amount of Am and Pu obtained by this technique is found to be superior compared to other techniques even in the presence of Th, U and fission products.     

Measurements of fast neutron capture cross sections on <Superscript>63</Superscript>Cu and <Superscript>186</Superscript>W

Neutron capture cross sections on ⁶³Cu and ¹⁸⁶W were measured by fast neutron activation method at neutron energies from 1 to 2 MeV. Monoenergetic fast neutrons were produced by ³H(p,n)³He reaction. Neutron energy spread by target thickness, which was assumed to be the main factor of neutron energy spread, was estimated to be 1.5% at neutron energy of 2.077 MeV. Neutron capture cross sections on ⁶³Cu and ¹⁸⁶W were calculated by reference comparison method on those of ¹⁹⁷Au(n,γ). Not only statistical errors of gamma-counts from samples but also systematic errors in the counting efficiency for HP Ge detector and the uncertainty of areal density of samples were considered in calculating neutron capture cross section. Estimated neutron capture cross sections on ⁶³Cu and ¹⁸⁶W were also compared with ENDF-6 data.     

Simultaneous non-destructive determination of Al,Si and K in tungsten with 14 MeV neutrons

A non-destructive simultaneous method has been developed for the rapid determination of Al, Si and K in WO₃ powders and W metal powders. The samples were activated by 14 MeV neutrons and the radioactive isotopes identified by their γ-ray spectra with a 3″×3″ NaI(Tl) detector. Quantitative analysis was carried out by measuring the full energy peak areas. The determined concentrations of Al, Si and K were above 100, 100 and 500 ppm, the sensitivities being about 20, 10 and 100 ppm, respectively.     

Application of fast solvent extraction processes to studies of exotic nuclides

The nucleus²³Na has been investigated by studying the primary γ-rays emitted from 53 keV neutron capture in it using a high resolution and high efficiency (100%) HPGe detector and NaI(T1) detector for anti-Compton. 24 primary γ-rays were placed in the²⁴Na, in which 3 primary γ-rays were new ones from a (n, γ) reaction, and reported for the first time. In order to obtain an exact energy calibration within 7 MeV,⁵⁶Fe(n,γ)⁵⁷Fe reaction was used at thermal neutron energy. Intensity calibration was obtained from the²⁷Al(p,γ)²⁸Si reaction atE _p=2046 keV. The neutron binding energy of²⁴Na was determined to be 6959.75 keV.     

Determination of fluorine in organic compounds by epithermal neutron activation analysis

Classical activation analysis of fluorine by thermal neutrons has a limited application because of frequent interference from chlorine, the short half life²⁰F (11.4 s) and too high dead time of detectors. A procedure is described for fluorine determination using¹⁹F (n,p)¹⁹O reaction. Use of a boron carbide shield has no effect on the activity of¹⁹O (boron ratio −1) but considerably reduces background and interference due to¹⁸O (n, γ)¹⁹O reaction. The technique has been successfully applied to the determination of fluorine in organic compounds even in the presence of large amounts of chlorine and oxygen.     

Simultaneous elemental determination of aluminum and silicon in soils by gamma-ray detection following inelastic neutron scattering

The detection of prompt γ-rays produced by the inelastic scattering of fast monoenergetic neutrons has been used to determine the elemental composition of soil samples. Multigram samples were bombarded with 2.5 MeV neutrons, and concentrations were measured by analyzing the spectrum of emitted γ-rays. Particular emphasis has been placed on the simultaneous determination of aluminum and silicon. Possible extensions of the method to light elements are suggested.     

Utilization of cyclotron produced fast neutrons in the activation analysis for oxygen

The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the¹⁶O(n, p)¹⁶N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons. It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen. In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about 10¹⁰ n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent.