Optimized automated activation analysis

A combination of special techniques has been developed for optimization of experimental conditions in order to improve the analytical capability, to facilitate automation and to broaden the applicability of instrumental neutron activation analysis. The techniques used are: (1) compensation for the rapid radioactive decay of short-lived nuclides with the increase of the counting efficiency by automatic source movement to the detector during the counting period, to minimize count rate variations and to prolong the counting period, (2) repeated cyclic and cumulative activation to improve the counting statistics, (3) instrumental correction of counting losses at high and varying count rates by a loss-free counting system and (4) differentiation of the reactor neutron spectrum to enhance the counts from the nuclides of interest by reducing matrix interferences. By optimized combination and automation of these techniques significant improvement of the capability of instrumental neutron activation analysis can be achieved.     

Development of automated analytical systems for large throughput

The need to be able to handle a large throughput of samples for neutron activation analysis has led to the development of automated counting and sample handling systems. These are coupled with available computer-assisted INAA techniques to perform a wide range of analytical services on a commercial basis. A fully automated delayed neutron counting system and a computer-controlled pneumatic transfer for INAA use are described, as is a multi-detector gamma spectroscopy system.     

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.     

Activation analysis opportunities using cold neutron beams

Guided beams of cold neutrons being installed at a number of research reactors may become increasingly available for analytical research. A guided cold beam will provide higher neutron fluence rates and lower background interferences than in present facilities. In an optimized facility, fluence rates of 10⁹ n·cm^–2·s^–1 are obtainable. Focusing a large area beam onto a small target will further increase the neutron intensity. In addition, the shift to lower neutron energy increases the effective cross sections. The absence of fast neutrons and gamma rays permits detectors to be placed near the sample without intolerable background, and thus the efficiency for counting prompt gamma rays can be much higher than in present systems. Measurements made at the hydrogen cold source of the FRJ-2 (DIDO) reactor at the KFA provide a numerical evaluation of the improvements in PGAA with respect to signal-to-background ratios of important elements and matrices.     

Methods for preparing comparative standards and field samples for neutron activation analysis of soil

One of the more difficult problems associated with comparative neutron activation analysis (CNAA) is the preparation of standards which are tailor-made to the desired irradiation and counting conditions. Frequently, there simply is not a suitable standard available commercially, or the resulting gamma spectrum is convoluted with interferences. In a recent soil analysis project, the need arose for standards which contained about 35 elements. In response, a computer spreadsheet was developed to calculate the appropriate amount of each element so that the resulting gamma spectrum is relatively free of interferences. Incorporated in the program are options for calculating all of the irradiation and counting parameters including activity produced, necessary flux/bombardment time, counting time, and appropriate source-to-detector distance. The result is multi-element standards for CNAA which have optimal concentrations. The program retains ease of use without sacrificing capability. In addition to optimized standard production, a novel soil homogenization technique was developed which is a low cost, highly efficient alternative to commercially available homogenization systems. Comparative neutron activation analysis for large scale projects has been made easier through these advancements. This paper contains details of the design and function of the NAA spreadsheet and innovative sample handling techniques.     

Nuclear analytical methods in teaching and research at the University of Illinois

An overview of the nuclear analytical methods oppurtunities at the University of Illinois at Urbana-Champaign is given. Undergraduate and graduate level teaching and research are highlighted. The TRIGA reactor and neutron activation analysis facilities are described in the context of this role within an inter-disciplinary environment.     

Updating analytical techniques for fast neutron activation analysis

Two improvements in the analytical techniques used for fast neutron activation analysis have been developed and put into routine use. The first is neutron shielding of a NaI (TL) counting system, which reduces the counting noise encountered during neutron generation. The second is a modification of batch type irradiation for long lived nuclides so they can be done simultaneously with other test.     

Short-time neutron activation gamma-ray spectroscopy

Short-time instrumental neutron activation analysis, with high throughput, sensitivity and accuracy without matrix interferences, can be achieved in spite of the initial high count rate from both short and long-lived nuclide activation, if the experimental conditions are optimized by the combination of techniques. Thus the initial usually high counting rate can be faced by a loss-free counting system to avoid blocking or distortion of the system. The rapid radioactive decay and the consequent low counting statistics of short lived nuclides can be compensated by source-detector distance variation during the counting period and by cyclic and cumulative activation. Matrix spectral interferences can be reduced by ion exchange before activation for selective element preseparation and by neutron spectrum optimization such as epithermal neutron activation for selective element peak enhancement.     

Short-time neutron activation gamma-ray spectroscopy

Short-time instrumental neutron activation analysis, with high throughput, sensitivity and accuracy without matrix interferences, can be achieved in spite of the initial high count rate from both short and long-lived nuclide activation, if the experimental conditions are optimized by the combination of techniques. Thus the initial usually high counting rate can be faced by a loss-free counting system to avoid blocking or distortion of the system. The rapid radioactive decay and the consequent low counting statistics of short lived nuclides can be compensated by source-detector distance variation during the counting period and by cyclic and cumulative activation. Matrix spectral interferences can be reduced by ion exchange before activation for selective element preseparation and by neutron spectrum optimization such as epithermal neutron activation for selective element peak enhancement.     

High count rate gamma spectrometry. A summary of recent experiments in high accuracy NAA applications

A source of error in the gamma-spectrometric registration of the analytical signal in neutron activation analysis is its dependency on the overall count rate. Losses in the accuracy of quantitation occur due to hardware and software. This paper presents examples for solutions to these problems and demonstrates that accurate NAA can be accomplished under high-rate counting conditions with commercially available technology.     

Coincidence counting for PGNAA applications: Is it the optimum method?

Summary One of the main advantages of γ-γ coincidence counting is the reduction of the background spectrum, pulse pile-up, and summing effects (for simple schemes). For prompt gamma-ray neutron activation analysis (PGNAA), the sources of background include the gamma-rays from the natural background, from surrounding materials, from the neutron source, and from detector neutron activation. While this counting approach effectively increases the signal-to-noise (S/N) ratio, it also decreases the signal counting rate. This adds some practical limitations to using this approach. In this work, two examples are presented for the efficient use of the coincidence counting approach.     

The use of delayed nuclear track counting for determining bismuth

The predominant use of the nuclear track technique (NTT) in analytical chemistry has been to measure the prompt charged particle emission from neutron induced reactions with stable or fissile nuclides of selected elements. This work describes the use of the NTT for determining bismuth via delayed alpha particle emission from the decay of²¹⁰P. This technique is sensitive and reliable since alpha track counting is highly efficient and can provide information, on elemental spatial distributions. Bismuth determinations in various materials by this technique appears possible to at least the 1.0 microgram per gram level.     

Investigating the antimony determination in environmental samples by NAA

In recent years, environmental concerns regarding antimony have grown considerably due to anthropogenic processes that have resulted in increasing concentration of Sb in the environment, and also because of its impacts and possible adverse effects to living organisms. Several techniques have been used, to obtain reliable results for Sb, since Sb is present at low level concentration, requiring analytical instrumentation with low detection limits. The neutron activation analysis (NAA) technique has a high metrological level for the determination of several elements in different matrices. However, Sb determination in environmental and biological samples presents some analytical difficulties due to its low concentrations and gamma ray spectrum interferences. The objective of this research was to study on Sb determination in environmental reference materials by NAA. Ten environmental reference materials were selected and analyzed using long period irradiation at IEA-R1 research nuclear reactor. The induced gamma activities of ¹²²Sb and ¹²⁴Sb were measured. Relative errors of the results demonstrated that the accuracy depends mainly on Sb radioisotope measured, the decay time for counting and the sample composition.     

U determination in environmental samples by delayed neutron activation analysis in Korea

A delayed neutron counting system has been implemented at the HANARO research reactor in 2007. Thermal neutron flux measured at the NAA #2 irradiation hole coupled to the delayed counting system, was higher than 3 × 10¹³ n cm⁻² s⁻¹. The delayed neutron counting system is composed of 18 ³He detectors which are divided into three groups with six detectors and the collected signals of each group are processed to a digital signal. The count numbers were measured with the uranium mass by using NIST SRMs under fixed analytical condition and their correlation could be determined. Finally, delayed neutron activation analysis has been carried out for the determination of uranium mass fraction in the collected environmental samples.     

Broad Scope Educational Role of a Midsize University Reactor NAA Laboratory

Broad scope educational activities at the Neutron Activation Analysis Laboratory (NAAL) associated with the 100 kW University of Florida Training Reactor (UFTR) have been implemented to serve a diverse and multidisciplinary academic clientele to meet a wide spectrum of educational needs for students at all academic levels. Educational usage of the complementary laboratory facilities is described and the importance of such academic experimental experience is emphasized for developing and maintaining a cadre of professionals in the analytical applications of nuclear energy. The synergistic operation of the NAAL and the reactor at the University of Florida to serve as a model worthy of emulation for other similar facilities is emphasized.     

A pilot study to measure levels of selected elements in Thai foods by instrumental neutron activation analysis

A pilot study was carried out to evaluate the scope of instrumental neutron activation analysis (INAA) for measuring the levels of selected elements in a few commonly consumed food items in Thailand. Several varieties of rice, beans, aquatic food items, vegetables and soybean products were bought from major distribution centers in Bangkok, Thailand. Samples were prepared according to the protocols prescribed by the nutritionist for food compositional analysis. Levels of As, Br, Ca, Cd, Cl, Cr, Cu, Fe, K, Mg, Mn, and Zn were measured by INAA using the irradiation and counting facilities available at the Thai Research Reactor with the maximum in-core thermal neutron flux of 3 × 10¹³ cm^?2 s^?1 of the Thailand Institute of Nuclear Technology in Bangkok. Selenium was determined by cyclic INAA using the Dalhousie University SLOWPOKE-2 Reactor facilities in Halifax, Canada at a thermal neutron flux of 2.5 × 10¹¹ cm^?2 s^?1. Both cooked and uncooked foods were analyzed. The elemental composition of food products was found to depend significantly on the raw material as well as the preparation technique.     

Progress in methods for the identification of explosives in Russia

The progress in analytical methods for the determination of explosive done by Russian scientists is reviewed: gas analytical; nuclear physical, including neutron activation analysis; nuclear quadruple resonance (NQR); and optical spectroscopy.     

Upgrade of the prompt gamma activation analysis and the neutron-induced prompt gamma spectroscopy facilities at the Budapest research reactor

The Budapest Research Reactor’s Prompt Gamma Activation Analysis (PGAA) and Neutron-Induced Prompt gamma Spectroscopy (NIPS) facilities were significantly upgraded during the last few years. The higher neutron flux, achieved by the partial replacement and realignment of the neutron guides, made feasible the automation and specialization of the two experimental stations. A new neutron flux monitor, computer-controlled beam shutters and a low-level counting chamber have been put into operation to assist with in-beam activation experiments. An automatic sample changer has been installed at the PGAA station, while the NIPS station was redesigned and upgraded with a Compton suppressor to use for the non-destructive analysis of bulky samples. In the near future the latter setup will be completed with a neutron tomograph and a moving table, to turn it into a Neutron Radiography/Tomography-driven PGAA equipment.     

Application of an image scanner for determination of boron in glass by a nuclear track technique

For boron concentration in the range of 010%, a 600 g²⁵²Cf neutron source was used for thermal neutron irradiation. As for the track counting technique, a visual observation method by human eye and an automatic counting method with an image scanner showed a good agreement between the determinations by both methods. The latter is useful for improving accuracy in elemental determination by using the nuclear track technique because it gives reproducible count values which are free from human error in comparison with the former.     

Methodological developments and applications of neutron activation analysis

The paper reviews the author’s experience acquired and achievements made in methodological developments of neutron activation analysis (NAA) of mostly biological materials. These involve epithermal neutron activation analysis, radiochemical neutron activation analysis using both single-and multi-element separation procedures, use of various counting modes, and the development and use of self-verification principle. The role of NAA in the detection of analytical errors is discussed and examples of applications of the procedures developed are given.