Neutron spectrum parameters in irradiation channels of the Nigeria Research Reactor-1 (NIRR-1) for the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA standardization

Summary The first nuclear research reactor in Nigeria has been commissioned for neutron activation analysis and limited radioisotope production. In order to extend its utilization to include the k₀-standardization method, the following neutron spectrum parameters in inner and outer irradiation channels were determined by the “Cd-ratio for multi-monitor method”: the thermal-to-epithermal flux ratio, f, and the epithermal flux shape factor, α. Neutron spectrum parameters determined in the inner irradiation channel B2, are: α = -0.052±0.002 and f = 19.2±0.5. For the outer irradiation channel B4, the neutron spectrum parameters were found to be α = +0.029±0.003 and f = 48.3±3.3. The results are compared with the neutron spectrum parameters of other reactor facilities with similar core configuration such as the Slowpoke and Miniature Neutron Source Reactor facilities available in the literature.     

Determination of impurities in zircaloy clad by means of neutron activation analysis

A method is described for determining impurities in Zr-2 and Zr-4 clads by means of instrumental neutron activation analysis followed by high resolution gamma-ray spectrometry. The samples were irradiated in IRT-5000 using vertical channels and a pneumatic system with neutron fluxes of about 3·10¹³ and 4.8·10¹¹ n·cm^–2·s^–1, respectively, and counted using Ge(Li) detectors coupled to an on-line computer. The following impurties have been determined Al, Cr, Mn, Fe, Co, Ni, As, Sn, Sb, Hf and W.     

Experimental and MCNP calculations of neutron flux parameters in irradiation channel at Es-Salam reactor

The Algerian research reactor (Es-Salam) is a 15 MW heavy water reactor type, operating since 1992. It became essential to characterize the neutron field in the most useful irradiation positions, in order to guarantee the accuracy in the application of k ₀-neutron activation analysis (k ₀-NAA). Experimental value of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from 1/E shape (α) were determined using different methods. This work focuses the verification of Monte Carlo neutron flux calculation in typical irradiation channel. Comparison of the results for parameter f obtained experimentally and by Monte Carlo simulations shows good agreement in the irradiation channel studied. The difference between both results is about 2.08%.     

Instrumental neutron activation analysis of Moroccan geological samples using the k0-standardization method

Instrumental neutron activation analysis (INAA) for traces and major elements of several geological samples from “Zgounder” region in Morocco was performed utilizing the k ₀-standardization method. Sample irradiation has been done by the 250 kW Triga Mark II reactor at Jozef Stefan Institute in Slovenia. Due to its accuracy, sensitivity and specificity, the k ₀-standardization method is the most suitable method for non-destructive multielement analysis mainly for trace elements in rocks. It requires an accurate knowledge of the parameters of the irradiation facilities and other instrumentation parameters. It is an absolute standardization method, where the absolute nuclear data are replaced by a nuclear constant, the k ₀-factor, determined experimentally with high accuracy. More than 40 elements were determined using about 30-second short and about 7-hour long irradiations. Gamma-rays emitted from the irradiated samples have been determined by a high purity germanium detector. Accuracy was assessed using the standard reference material AGV-1. This was less than 1% for major elements and about 5% for traces. This revised version was published online in July 2006 with corrections to the Cover Date.     

Activation Constants for Slowpoke and MNS Reactors Calculated from the Neutron Spectrum and k0 and Q0 Values

The relative thermal, epithermal and fast neutron fluxes were measured in the inner and outer irradiation sites of three Slowpoke reactors and one Miniature Neutron Source (MNS) reactor by the bare triple monitor method. Using the measured neutron spectrum parameters and a compilation of published k ₀ and Q ₀ values, activation constants were calculated for the most intense gamma-rays of all nuclides commonly used in NAA. The resulting table of constants can be used to standardize NAA measurements for all elements when combined with relative efficiency measurements and the measurement of the thermal neutron flux with one standard. The observed constancy of the neutron spectra suggests that these activation constants are valid for all 14 Slowpoke and MNS reactors.     

Implementation of <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-standardization method of the INAA at ETRR-2 research reactor

The k ₀-method of INAA standardization has been implemented using the irradiation facilities of the fast pneumatic rabbit and some selected manually loaded irradiation positions, which designated for short and long irradiation, respectively, at Egypt second research reactor. The neutron flux parameters (f and α) in each site have been determined using Zr–Au sets as neutron flux monitors. The reference materials coal NIST 1632c and IAEA-Soil 7 were analyzed for data validation and good agreement between the experimental values and the certified values was obtained.     

Neutron flux and associated k0 parameters in the RPI after the last configuration change

The Portuguese Research Reactor (RPI) is a 1 MW swimming pool type reactor, operating since the early 1960s. The fuel is MTR type, with flat plates of U-Al alloy enriched to 93% in ²³⁵U. As the core configuration changed in April 2000, it became essential to characterise the neutron field in the most useful irradiation positions of RPI, in order to guarantee the accuracy in the application of k ₀-neutron activation analysis (k ₀-NAA). Experimental values of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from the 1/E shape (a) were determined using the Cd-ratio for multi-monitor method. The neutron temperature (T _n) was obtained from co-irradiation of Lu with 1/v monitors. The results for several irradiation positions are presented and discussed in this work. Some element concentrations are determined based on the parameters obtained in this work, and compared with the certified reference material concentrations.     

Serum aluminum determination by instrumental neutron activation analysis in long-term haemodialysis patients

Serum aluminum levels were determined by instrumental neutron activation analysis in 31 patients undergoing long-term haemodialysis. Aluminum-28 1.778 MeV (T _1/2=2.24 min) γ-rays produced by the thermal neutron reaction²⁷Al(n,γ)²⁸Al were detected. Successive irradiation of the samples at epithermal neutron fluence was performed to correct for the interference from the fast neutron reaction³¹P(n,α)²⁸Al. Serum aluminum level in this group of subjects was adequately represented by a lognormal distribution with a mean and variance of 16.5 μg/l and 16.8 μg/l, respectively. The results obtained were found to be in agreement with serum aluminum determination performed by electrothermal atomic absorption spectrophotometry (r ²=0.97). Instrumental neutron activation can provide a rapid technique to routinely monitor long-term haemodialysis patients in order to identify individuals at greater risk to develop aluminum toxicity.     

Determination of mass fractions of 12 elements in more common apple varieties in Iran by instrumental neutron activation analysis

In this study, the amount of 12 elements in five widespread varieties of apples (Malus pumila) used in the Arak markets in Iran (Uromieh golden apple—Maragheh golden apple—Semirom golden apple, Semirom green apple, Semirom red apple) were determined using the instrumental neutron activation analysis method. In this work, the Tehran research reactor was used as a source of thermal neutron flux. The highest concentrations of Cl, K, Mg, Na and Zn were detected in Maragheh golden apple which indicates that from the point of view of nutrition, the best cultivar of studied apples is Maragheh golden apple.

     

The Simultaneous Determination of Ruthenium and Osmium by A Radiochemical Method

Abstract

A simple radiometric procedure is proposed for the determination of raicrogram amounts of ruthenium and osmium by the use of neutron activation. Alter irradiation, the tetroxides of both metals were collectively distilled and then determined directly by measuring the photopeak areas of osmium-191 and ruthenium-103 at 45 and 498 Kev respectively. The effect of Compton continua was negligible.     

Automatic NAA: Saturation activities

A system for Automatic NAA is based on a list of specific saturation activities determined for one irradiation position at a given neutron flux and a single detector geometry. Originally compiled from measurements of standard reference materials, the list may be extended also by the calculation of saturation activities from k ₀ and Q ₀ factors, and f and a values of the irradiation position. A systematic improvement of the SRM approach is currently being performed by pseudo-cyclic activation analysis, to reduce counting errors. From these measurements, the list of saturation activities is recalculated in an automatic procedure.     

Using synthetic multi-element standards (SMELS) for calibration and quality control of the irradiation facilities in the BR1 reactor

The thermal to epithermal neutron flux ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape (α) are essential parameters for the correct application of k ₀-standardized neutron activation analysis. Several methods are applied for the determination of f and α. They are based on Cd-covered multi-monitor or on bare-irradiations methods. The recently developed and characterized synthetic multi-element standards (SMELS) were designed as a validation tool for the proper implementation of the k ₀-NAA method in a laboratory. In particular, SMELS Type III contains Au and Zr, thus allowing the direct determination of f and α. It could, therefore, replace the traditional flux monitors. Furthermore, it could be used as a quality control material to monitor the stability of the irradiation facility and the detector. This paper presents the accuracy of the f and α determination and the feasibility of quality control using SMELS for irradiation channel Y4 of the BR1 reactor.     

The determination of sulphur and phosphorus in steel by neutron activation analysis

Sulphur and phosphorus in steel were determined by neutron activation analysis, being counted as ³⁵S and ³²P respectively. For steels with sulphur to phosphorus ratios larger than 10, it seems possible to determine both elements by counting ³²P, making use of a double irradiation technique at different fast to slow neutron fluxes.     

Calibration of the irradiation channel DBVK at BER-II reactor and feasibility of applying the k0-method at this device

This work is about k ₀-INAA using unstable neutron flux for sample irradiation. Due to slow transport, each irradiation in the channel DBVK consists of three phases: stable irradiation at the final position, and two additional irradiations during travelling by exposure to an increasing neutron flux in the delivery course and to a decreasing neutron flux in the fetch course. In this work, the neutron flux distribution along this channel was calibrated and the neutron flux variation with irradiation time was calculated, making it possible to evaluate activity growth during a complete irradiation period. The feasibility of the k ₀-method was checked by analyses of four SRM-materials and three multi-element standards at three DBVK-positions. An accuracy of better than ±10% was found for nearly all determined elements in each determination.     

Determination of total mercury in environmental and biological samples using k0-INAA, RNAA and CVAAS/AFS techniques: Advantages and disadvantages

The accuracy and precision of the results obtained for total mercury in various environmental and biological samples and certified reference materials (CRMs) by various analytical methods, including k ₀-instrumental neutron activation analysis (k ₀-INAA), radiochemical neutron activation analysis (RNAA) and cold vapour atomic absorption (and atomic fluorescence) spectrometry (CVAAS/AFS) used in routine analysis in our laboratory, were investigated. Three natural matrix reference materials (RMs) from the International Atomic Energy Agency (IAEA), five CRMs from the Institute for Reference Materials and Measurements (IRMM), six CRMs from the National Institute of Standards and Technology (NIST) and one from the Jožef Stefan Institute (IJS) were analyzed. The results obtained show good agreement between certified or assigned values, and between the methods used, except for some data obtained by k ₀-INAA in biological samples. This can be explained by losses during irradiation in semi-open systems (irradiation in plastic ampoules) and/or spectral interferences. This revised version was published online in August 2006 with corrections to the Cover Date.     

Second-order interference in the neutron activation analysis of arsenic in a germanium matrix

The second-order interference ⁷⁴Ge(n, γ; β^-, n, γ)⁷⁶ As can occur in the activation analysis of arsenic in a germanium matrix, using thermal neutrons. As the literature data show poor agreement, this interference was determined experimentally. A practical formula was derived, for irradiation times longer than 2 h, which showed that the interference, expressed as an apparent arsenic concentration, is proportional to the neutron flux. Experiments were performed for irradiation times of 10, 15 and 20 h at a neutron flux of 10¹⁴ n/cm²/sec, yielding apparent arsenic concentrations in the germanium matrix of respectively 223, 408 and 597 p.p.b. From these results a value of 0.48 ±0.06 barn could be calculated for the activation cross-section of ⁷⁴Ge for neutron capture.     

Neutron activation analysis for determination of metal ions in biological fluids of patients after CoCrMo arthroplasty

Determination of metals and trace elements in patients with total knee or hip arthroplasty with CoCrMo alloy was performed. Blood, urine and cerebrospinal fluid (CSF) samples were analyzed and compared with samples from healthy people. Levels of Co, Cr as well as Na, Ca, Fe, Zn, Se, Rb, Sb and Br were determined by means of neutron activation analysis. The values of Cr and Co of the blood and urine measurements were elevated in patients with replacement, and according to the statistical analysis, significant differences of the elements Zn, Br, Co and Sb were found in the CSF (p?<?0.05).

     

Neutron flux characterization of the Moroccan Triga Mark II research reactor and validation of the k 0 standardization method of NAA using k 0-IAEA program

The aim of this work was to implement and to validate the k ₀ standardization method in neutron activation analysis (k ₀-NAA) at the Moroccan TRIGA Mark II research reactor. This technique was used in order to determine, the calibration of several HPGe detectors and calibration of neutron flux parameters in the typical irradiation channels [rotary specimen rack (RSR) and the pneumatic tube system (PTS) facilities]. Calibrations and calculations of k ₀-NAA results were carried out using the k ₀-IAEA program. The two parameters of neutron flux in the selected irradiation channels used for elemental concentration calculation, f (thermal-to-epithermal ratio) and α (deviation from the 1/E distribution), have been determined as well in the PTS as in the RSR facilities using the zirconium bare triple method. Results obtained for f and α in two irradiation channels show that f parameter determined in this way is different in the RSR and the PTS facilities. This can be explained by the fact that the RSR channel is situated in a graphite reflector and is relatively far from the reactor core, while the PTS is in the core. Five reference materials of different origin obtained from USGS (basalt BE-N, bauxite BX-N, biotite mica-Fe, granite GS-N) and IAEA (Soil-7) were used to evaluate the validity of this method in our laboratory by analyzing the elemental concentrations with respect to the certified values. In general, good agreement was obtained between results of this work and values in certificates of the individual reference materials, thus proving the accuracy of our results and successful implementation of the method for analysis of real samples.     

Forty-five years of neutron activation analysis in Slovenia: achievements towards improved quality of measurements results

Main achievements towards improved quality of measurements results obtained by neutron activation analysis (NAA) at the TRIGA Mark II reactor of the Jožef Stefan Institute during its 45 years of continuous operation are reviewed from a historical perspective; emphasis is on the features specific for NAA. The development of radiochemical neutron activation analysis for characterising reference materials is described in detail in the first part. Several approaches specific for the method such as the determination of long-lived radionuclides, the simultaneous determination of several elements using double irradiation and the internal standard method are presented in more detail. Several interesting approaches such as combination with liquid scintillation counting detection and combination with radiometric measurements are outlined. Then, the development of instrumental neutron activation analysis, specifically the k ₀-NAA based method is discussed. The contribution towards methodological development of uncertainty assessment is outlined, and the importance of the nuclide-specific and neutron fluence-specific approach is emphasised. Throughout the paper, the importance of neutron activation analysis and contributions of measurements results obtained by this method to characterising (candidate) reference materials is shown.     

Determination of characteristic neutron flux parameters of nuclear reactors for thermal neutron activation analysis

The characteristic neutron spectrum parameters for thermal neutron activation analysis have been determined for the most important irradiation positions of the reactors BR1 and BR2 at Mol (Belgium), HFR at Petten (Netherlands) and FRJ2 at Jülich (Federal Republic of Germany). The method of determination is described.