Neutron activation analysis with radiochemical separation

Trace Elements in Coal by Neutron Activation Analysis with Radiochemical Separations... 

Procedures for the determination of 11 elements in coal—Sb, As, Br, Cd, Cs, Ga, Hg, Rb, Se, U, and Zn—by neutron activation analysis with radiochemical separation are summarized. Separation techniques include direct combustion, distillation, precipitation, ion exchange, and solvent extraction. The evaluation of the radiochemical neutron activation analysis for the determination of mercury in coal used by the Bureau of Mines in its mercury round-robin program is discussed. Neutron activation analysis has played an important role in recent programs to evaluate and test analysis methods and to develop standards for trace elements in coal carried out by the National Bureau of Standards and the Environmental Protection Agency. 

As mentioned before, two interlaboratory studies were organised prior to certification, involving ca. 15 laboratories using techniques such as cold vapour atomic absorption spectrometry, direct current plasma atomic emission spectrometry (DCP-AES), differential pulse anodic stripping voltammetry (DPASV), microwave plasma atomic emission spectrometry (MIP-AES), electrothermal atomic absorption spectrometry (ETAAS) and neutron activation analysis with radiochemical separation (RNAA). 

RNAA Neutron activation analysis with radiochemical separation... 

Nuclear Methods - Neutron Activation Analysis with Radiochemical Separation (RNAA)... 

Some relevant terms for activation analysis are activation analysis, neutron activation analysis (NAA), instrumental neutron activation analysis (INAA), neutron activation analysis with radiochemical separation (RNAA), photon activation, neutron capture prompt gamma activation analysis (PGAA), charged particle activation, autoradiography, liquid scintillation counting, nuclear microprobe analysis, radiocarbon (and other element) dating, radioimmunoassay, nuclear track technique, other nuclear and radiochemical methods. Briefly, the salient features of some of the more popular techniques are as follows ... 

Gallium may be estimated in low-temperature coal ash by neutron activation analysis, with radiochemical separation. Amounts in the range 1—10 p.p.m. were determined. 

Dyhczynski, R.S. 50 years of adventures with neutron activation analysis with the special emphasis on radiochemical separations. J. Radioanal. Nucl. Chem. 303, 1067-1090 (2015). doi 10.1007/sl0967-014-3822-6... 

The availability of high flux thermal neutron irradiation facilities and high resolution intrinsic Ge and lithium drifted germanium (Ge(Li)) or silicon (Si(Li)) detectors has made neutron activation a very attractive tool for determining trace elemental composition of petroleum and petroleum products. This analytical technique is generally referred to as instrumental neutron activation analysis (INAA) to distinguish it from neutron activation followed by radiochemical separations. INAA can be used as a multi-elemental method with high sensitivity for many trace elements (Table 3.IV), and it has been applied to various petroleum materials in recent years (45-55). In some instances as many as 30 trace elements have been identified and measured in crude oils by this technique (56, 57). 

The fundamental principle behind analysis by activation analysis is activation or excitation of an atomic nucleus by exposure to radiation such as neutrons, protons or high-energy photons with subsequent measurement of emitted sub-atomic particles or radiation. The most common aspect of the technique involves activation with neutrons in a nuclear reactor and measurement of delayed emitted gamma rays, denoted neutron activation analysis, either instrumental neutron activation analysis (INAA) or neutron activation followed by radiochemical separation (RNAA) in which the element of interest is chemically separated from the matrix after irradiation to provide for better, unimpeded counting. 

Neutron activation analysis (NAA) with a rapid radiochemical separation has been the method generally used in recent years, but requires substantial investment, has high operating cost and limited availability. Modem flameless atomic absorption (AAS) instruments provide sensitivity approaching that of NAA and offer a viable alternative for the detection of firearms discharge residue. 

It is generally agreed that neutron activation analysis has shown great sensitivity for many elements. Absolute sensitivities of detection depend on the atomic weight of the element, the fractional abundance of the target nuclide, and its cross section for thermal neutrons (which are fixed values) as well as on the available neutron flux, the irradiation time, the decay period, and the counting efficiency of the detector (which are variable parameters). The formulae described under Fundamentals (vide supra) will make it clear that, unless conditions are exactly specified, published values cannot easily be compared especially as the definitions for sensitivity chosen by the investigators may be different. Experimental sensitivities may be idealized because of matrix problems, difficulties in radiochemical separations, and other analytical problems associated with the analysis of complex, real samples. 

After the cooling period, the sample is either counted directly or some chemical manipulation is performed before counting. The first procedure is known as instrumental neutron activation analysis (INAA), whereas the latter is referred to as radiochemical neutron activation analysis (RNAA). In RNAA a stable carrier for the element to be determined may be added to the sample after irradiation. The carrier is equilibrated with the element in the sample (often by fusing it with Na202, or treating it with strong acid). Then the element of interest is separated along with the carrier. The chemical yield of the separation is determined from the amount of carrier recovered, and this correction is applied to the measured activity. 

In radiochemical activation analysis (RAA), the various techniques of activation analysis (AA), i.e., neutron activation analysis (NAA), photon activation analysis (PAA), and charged particle activation analysis (CPAA) are combined with radiochemical separation procedures with the intention of extending the capabilities offered by the purely instrumental methods. 

The second step in neutron activation analysis is the measurement of the induced radioactivity. A number of different techniques have evolved over the years to keep pace with changes in technology. The techniques can be divided into two groups radiochemical neutron activation analysis (RNAA), a destructive technique in which various elements are separated after the irradiation, and instrumental neutron activation analysis (INAA), a non-destructive technique in which the activity in the sample is measured directly, relying on differences in y-ray energy and half-life to discriminate the various nuclides. 

Trace gold determination by on-line preconcentration with flow injection atomic absorption spectrometry, by use of di(methylheptyl)methyl phosphonate (DMHMP) as the immobilized phase loaded onto a macroporous resin Radiochemical separation and determination of gold complex matrices employing substoichiometric thermal neutron activation analysis... 

Geochemists were some of the first researchers to realize the enormous benefits of ICP-MS for the determination of trace elements in digested rock samples. Until then, they had been using a number of different techniques, including neutron activation analysis (NAA), thermal ionization mass spectrometry (TIMS), ICP-OES, x-ray techniques, and GFAA. Unfortunately, they all had certain limitations, which meant that no one technique was suitable for all types of geochemical samples. For example, NAA was very sensitive, but when combined with radiochemical separation techniques for the determination of rare earth elements, it was extranely slow and expensive to run. TIMS was the technique of choice for carrying out isotope ratio studies because it offered excellent precision, but unfortunately was painfully slow. Plasma... 

A special place is reserved for methods of activation analysis, involving slow and fast neutrons, charged particles, or photon.s, applied either directly or in combination with some type of radiochemical separation (Section 1.6.13). These methods quickly became almost indispen.sable, especially in extreme trace analysis of the ele-... 

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