Investigation on effects of operating conditions in combined activation of char to develop the pore structure

In this study, activation of pistachio shell char was investigated by chemical, physical and combined activation experimentally using a TGA instrument and lab scale reactor. The effects of operating conditions such as activation time, temperature and impregnation ratio in the activation methods were studied via the weight loss and iodine number of the samples. The results showed that combined activation is the premium activation method. In addition, in this method. a temperature of 800 °C, a dwell time of 45 min and an impregnation ratio of 50 % are the optimum conditions which give a product with an iodine number of 2433 mg/g and a weight loss 52 %. A high iodine number of this activated carbon was developed at a moderate temperature and dwell time, and the weight loss confirms the advantages of the combined activation method. The products were characterized by SEM and FTIR analyses.     

Some aspects of quality assessment of the k0-based method of NAA

Neutron activation analysis is one of the analytical techniques often used for certification of reference materials. The k₀-based method of instrumental neutron activation analysis can also be applied in intercomparison runs in the certification process and therefore it is desirable to know its accuracy in advance. Possible systematic errors related to the application of nuclear data at given neutron flux rate parameters, that can affect the uncertainties of the results obtained by this specific method, are elucidated and error propagation factors calculated for a typical irradiation position in the TRIGA Mark II reactor of the Jozef Stefan Institute. It was found that these uncertainties are at the level of 1–2% on the average.     

Corrections for neutron activation analysis with non-1/v nuclides using reactor moderator temperature readings

Neutron activation analysis using the single comparator method or the k ₀ method may be less accurate in the cases of non-1/v nuclides if irradiations are done at varying reactor temperatures. We propose a method to correct this effect, using available reactor moderator temperature readings. It was verified by the irradiation of two non-1/v nuclides, ¹⁷⁶Lu and ¹⁵¹Eu. Irradiations were carried out in two irradiation sites at two reactor powers and at estimated neutron temperatures varying from 18 to 46 °C. In all cases the measured activities showed a variation with temperature consistent with published tables of the variation of the Westcott g-factor. The method should be accurate to 1% for most small reactors and eliminates the need to irradiate temperature monitors.     

Trace element determination in high-purity aluminum clad samples by k 0-based internal monostandard instrumental neutron activation analysis

The k₀-based internal monostandard instrumental neutron activation analysis (IM-INAA) method was applied for quantification of trace impurities in seven high purity aluminum samples used as fuel cladding in a research reactor. Samples along with BCS CRM 182 (Si–Al alloy) were irradiated in high flux reactor neutrons for 10–15 h. In situ detection efficiency, needed in concentration calculation ratio by IM-INAA, was obtained using gamma rays of activation products produced in the samples. Elemental concentration ratios obtained with respect to Fe (used as internal monostandard) were converted to absolute concentrations by determining concentration of Fe by relative method of NAA. Concentrations of ten trace elements (Sc, Cr, Co, Zn, Ga, La, Ce, Sm, W and Hf) including major element Fe were determined in this work. The method used is non-destructive in nature and does not need multielement standards. Results of IM-INAA were compared with those obtained by relative method of INAA and inductively coupled plasma atomic emission spectrometry (ICP-AES). Details of methodologies and results obtained by all methods are discussed and compared in the paper.     

Determination of concentrations of U and Th in their mixed oxides by INAA methods

Uranium and thorium mixed oxides are being prepared using natural U and Th for studies on fuels for Advanced Heavy Water Reactors, wherein composition of U and Th is specific and requires strict control in terms their contents and homogeneity. Chemical quality control necessitates accurate and precise compositional characterization of the fuel material by a suitable analytical method. Among various analytical methods for U and Th, instrumental neutron activation analysis (INAA) is one of the best methods for their simultaneous determination without chemical dissolution and separation. INAA methods using reactor neutrons namely thermal NAA and epithermal NAA were standardized for the determination of U and Th in their mixed oxides. Standards, synthetic samples and U–Th mixed oxide samples, prepared in cellulose matrix, were irradiated at pneumatic carrier facility of Dhruva reactor as well as at self serve facility of CIRUS reactor under cadmium cover (0.5 mm). Radioactive assay was carried out using a 40% relative efficiency HPGe detector. Both activation and daughter products of ²³⁸U (²³⁹U and ²³⁹Np) and ²³²Th (²³³Th and ²³³Pa) were used for their concentration determination. The method was validated by analyzing synthetic samples of 6–48%U–Th mixed oxides. The standardized method was used for the concentration determination of U and Th in 4–30%U–Th mixed oxide samples. Results of U and Th concentrations including associated uncertainties obtained from the INAA methods are presented in this paper.     

A feasibility study to measure low levels of boron in selected Canadian and Japanese foods by prompt gamma activation analysis using the JAEA JRR-3 facility

A feasibility study was carried out to evaluate the potential of the thermal neutron capture prompt-gamma activation analysis (PGAA) for the measurement of low levels of boron in selected Canadian and Japanese foods using the PGA facility at the JRR-3 reactor of the Japan Atomic Energy Agency (JAEA) in Tokai. A method was optimized for this purpose. It is rapid and can be used without any chemical separation. The precision and accuracy of the method are good. The detection limit is around 0.5 mg kg^?1.     

Determination of polychlorinated biphenyls by neutron activation and gamma ray spectrometry

A new method for the determination of polychlorinated biphenyls in transformer oils has been developed. It is based on neutron activation of chlorine in a nuclear reactor and its determination by gamma ray spectrometry. Any organic chlorides present must be purged by volatilization. The method has been tested by analyzing 38 samples of transformer oil by gas chromatography and by this technique. Each time the concentration of chlorine was higher than 38 ppm, the oil was found to be contaiminated by the PCBs. This method provides a fast and cost effective analysis of transformer oils.     

The determination of ko factors and their application to the neutron activation analysis of pure zirconium metal by the single-comparator method

The procedures followed for the determination of standardization factors and their use in the single-comparator method for multi-element reactor neutron activation analysis are described. The method is applied to the determination of Cr, Mn, Fe, Ni and Mo in pure zirconium metal. The matrix could serve as the single comparator and as a bi-isotopic thermal-to-epithermal neutron flux ratio monitor.     

Determination of vanadium in high grade carbons by radioanalytical methods

The present work deals with the determination of vanadium in high grade carbons by three radioanalytical methods, viz. thermal neutron activation analysis with an accelerator, thermal neutron activation analysis with a reactor and proton induced X-ray emission analysis with an accelerator. It is cleared from this study that thermal neutron activation with an accelerator is more convenient for the rapid and non-destructive analysis of ppm-level vanadium in bulk carbons than thermal neutron activation analysis with a reactor. Proton induced X-ray emission is less useful for the analysis of bulk samples.     

Determination of trace elements in biological materials by instrumental epithermal neutron activation analysis

The use of reactor epithermal neutrons in instrumental activation analysis is described for the determination of trace elements via long-lived isotopes. A boron carbide filter is used. Results of analyses of human erythrocytes, plasma, urine and some biological reference materials are given to demonstrate the applicability of the method to biological samples. Bromine, iron, cesium, rubidium, selenium and zinc and cobalt are determined. The method provides accuracy and reliability similar to conventional thermal neutron activation but is faster. Limits of detection attainable with the two techniques are compared.     

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.     

Cold neutron facility for prompt gamma-neutron activation analysis

The restart of the recently upgraded research reactor in Budapest is foreseen at the end of this year. A number of fast, thermal and cold neutron beams will serve for research, industrial and educational activities. One of the cold neutron guide end positions will be utilized for neutron capture prompt gamma-ray activation analysis (PGAA). Further development of the PGAA method as well as new applications in environmental research, biology and medicine are planned.     

Determination of reactor neutron spectra with multicomponent activation detectors

A procedure is described for the functional fitting of reactor neutron spectra with C/Eⁿ and fission spectra. The method is applied to multicomponent activation detector measurements in a Triga research reactor. In multicomponent detectors a mixture of several detector materials is irradiated as a single unit and measured simultaneously for all reaction products with a Ge(Li) gamma ray spectrometer.     

NAA for applied investigations at FLNP JINR: present and future

Experience in applying conventional and epithermal neutron activation analysis for some challenging areas of life sciences and material science is reviewed. For more than 30 years of its operation the radioanalytical complex REGATA at the IBR-2 reactor in Dubna has become a source of analytical data for the environmental studies, marine geology, biotechnology and medicine, technological process of diamond and boron nitride synthesis, archaeology, nanomaterials, etc. In spite of competing non-nuclear analytical techniques (AAS, ICP-ES, ICP-MS, etc.), the reactor neutron activation analysis (NAA) as a primary (ratio) method continues to be the most powerful multielement analytical technique providing quantification of trace elements at ultralow levels. Combined with modern statistical data treatment of large arrays of data, GIS (geographic information system) technologies, electron scanning microscopy, tomography, and others, NAA serves to obtain actual, practical results resumed in the review. The perspectives of using the upgraded reactor IBR-2M for analytical investigations are discussed.     

Determination of Zinc(II) ions with a reactor containing immobilized carboxypeptidase a in a flow system

Zinc(II) was determined in the range 2–20 × 10^?7 M through its activation of immobilized, metal-free carboxypeptidase A. The activity was assessed by injection of hippuryl-l-phenylalanine and the decomposition product was determined by high-performance liquid chromatography. Cadmium(II) and mercury(II) depressed the zinc response of the method although there was excess of metal-free enzyme in the reactor. Regeneration was made by pumping a 1,10-phenathroline solution through the reactor between successive samples.     

Analysis for trace elements with a slowpoke reactor

The SLOWPOKE reactor is very useful for neutron activation analysis and has been in operation at Dalhousie University for ten years. Improvements to the reactor are out-lined and flux evaluations after major changes are reported. Its use for the determination of trace elements in a broad variety of materials is described.     

程序升温连续流动反应器技术及其应用

在运用连续流动反应(CFR)技术(尾气技术)的基础上提出了1种可筛选催化剂并能进行非均相催化动力学研究的实验原理和方法--程序升温连续流动反应器(TPCFR)技术。在用此法筛选过的Cu-Ni催化剂上对甲醇分解反应和甲醇水蒸汽重整反应进行了系统研究,证明这种方法合理、可信。利用1条TPCFR曲线可求出各个动力学参数。     

Non-destructive analysis of phosphorus by neutron activation analysis in biochemical products

A method of neutron activation analysis is described for the quantitative determination of phosporus in nucleic acids, nucleotides and glucose-6-phosphate in amounts of 0.1 to 200 μg, without any chemical separation. This technique may be usefully applied to the measurement of the phosporus content in organic materials and biochemical preparations. The procedure involves a short neutron activation in a nuclear reactor and measurement of the Cerenkov radiation emitted by the irradiated capsule after a suitable decay period. Possible interferences due to other induced radionuclides are discussed.     

Problems in applying secondary reactions to the activation analysis of semiconductor surface layers

Investigations have been made concerning the determination of special contaminants (e.g. oxygen, boron) in the surface layers or epitaxially grown layers of semi-conductor crystals. These contaminants are insensitive to the conventional (n, γ) analysis and for their activation charged particles (e.g. t, α) from nuclear reactions induced by the capture of reactor neutrons are used. The specific particle yield from such reactions, e.g.⁶Li(n,t)α, was studied. The optimum conditions for the producing of activating layers (containing Li) and their optimum contact with the sample under investigation are discussed. Considering the so-called activation depth, a method was developed for the appropriate removal of the activated layer and the elements to be determined are subsequently separated from the semiconductor matrix by a fast chemical procedure. The combined activation cross sections measured on standard samples are given for different compositions and species of activating layers.     

热动力学方法测定端羟基聚丁二烯固化反应动力学参数

用热动力学方法对高分子固化反应动力学进行研究,在RD-Ⅰ型热导式自动量热计的基础上,设计了反应器,测定了端羟基聚丁二烯(HTPB)与甲苯二异氰酸酯(TDI)固化反应的动力学参数(表观活化能和反应速率常数),结果与文献值、粘度法和红外光谱法的结果相符。