At the beginning of the 20th century, with the discovery of natural radioactivity, we began to explore the use of natural radionuclides in analytical chemistry to simplify operations and improve the sensitivity of analysis. 1912 G. Huvish They first used radioactive lead (210Pb) as an indicator to determine the solubility of lead chromate. In 1925, R. Ellenburger used radioactive lead (212Pb) as an indicator to analyze natural lead by precipitation method. In 1932, Hervey et al Granite Before analyzing the sample, add radioactive lead with known specific activity to the sample solution isotope The results of lead analysis by dilution method are satisfactory. All these are radioactive indicators analytical chemistry The application in provides conditions. Subsequently, it is also widely used in extraction, precipitation, adsorption, titration, evaporation and other analytical operations. 1934 F. Jorio Curie and 1. Jorio Curie When artificial radioactivity was discovered, E. Fermi and others proposed that almost all elements can induce radioactivity under the action of thermal neutrons. In 1936, Hervey and H. Levy successfully analyzed impurities such as dysprosium in yttrium oxide and europium in gadolinium oxide by (n, γ) nuclear reaction for the first time, opening up a new field of activation analysis. Then, in 1938 G. T. Sieberg For the first time, et al. conducted charged particle activation analysis. With the establishment of reactors and various accelerators, the continuous improvement of multi-channel spectrometers and the popularization and application of microprocessors, activation analysis has been developed by leaps and bounds. Since the 1950s, microanalysis techniques (i.e Nuclear analysis technology ）。 Some of them study the microstructure of matter through the interaction between positrons and matter positron annihilation Technology, nuclear recoil free gamma ray resonance absorption -- Mossbauer effect -- application, as well as ion beam backscattering analysis, nuclear reaction analysis, channel effect application and particle excited X-ray fluorescence analysis developed in the 1970s. Radioanalytical chemistry has been paid attention to and developed rapidly due to its advantages of high sensitivity, small sampling volume and non destruction of samples. Methods commonly used in radioanalytical chemistry can be divided into two categories: ① methods using radioisotopes as indicators, such as radioanalytical method, radiochemical analysis, isotope dilution method, etc.; ② Methods such as activation analysis, particle excited X-ray fluorescence analysis, Mossbauer spectrum Nuclear magnetic resonance spectrum , positron annihilation and synchrotron radiation Etc. Using radionuclides Radiolabeled compound An analytical method used as an indicator to determine the content of non radioactive samples to be measured by measuring their radioactivity. Radioanalysis used in volumetric analysis is called Radioactive titration 。 It is a technology to determine the amount of radioactive substances contained in the sample by measuring radioactivity after separating and purifying the sample with appropriate methods. For example, the potassium content is determined by measuring the radioactivity of natural radionuclide potassium 40 (half life is 1.28 × 109 years, and the abundance is 0.111%). Isotope dilution method is used to mix the radioactive isotope or labeled compound with known specific activity and the same as the substance to be measured with the sample evenly, separate and purify part of it, and measure its specific activity. Calculate the content of the substance to be measured according to the change of specific activity before and after mixing, that is, isotope dilution multiple. (See Isotope dilution method 、 Sub stoichiometric analysis ） After the stable nuclides in the sample to be tested are converted into radionuclides by nuclear reaction Nuclear reaction cross section , particle Fluence rate , ray energy, half-life and radioactivity to determine the content of the substance to be measured. Can be divided into neutron activation analysis 、 Charged particle activation analysis And photon activation analysis. As a highly sensitive nuclear analysis technology, activation analysis is widely used in the analysis of biological samples and trace materials in high-purity materials, as well as in environmental science, archaeology, forensic science and other fields. The analytical sensitivity is 10-8~10-11g. Excited X-ray fluorescence analysis When α, β, γ or X rays act on the sample, due to coulomb scattering, orbital electrons absorb part of its kinetic energy, making the atom in an excited state. When the excited state returns to the ground state, the characteristic X-ray is emitted, and the type and content of elements are analyzed according to the energy and intensity of the characteristic X-ray. Its sensitivity is very high and it is widely used. (See X-ray fluorescence spectrometry ） µ sub X-ray fluorescence analysis
When a negatively chargedµ When a particle (µ -) is injected into the sample to be measured, it is trapped by the Coulomb gravity of the atomic nucleus to formµ Sub atoms also release a series of characteristic X-ray, namelyµ- X-ray, from which the chemical composition and state of the sample can be analyzed. (See µ Sub X-ray analysis ）
Mossbauer resonance spectrum
Namely, nuclear gamma ray resonance spectrum without recoil. Because of its high resolution, it can also measure the small changes in the state of extranuclear electrons, so it can obtain information about extranuclear electrons such as chemical shifts, intramolecular binding states, and intermolecular interactions. It has been used in the analysis of physical and chemical states of iron, tin, europium, thulium, tantalum, etc. (See Mossbauer spectroscopy ） Positron annihilation method
A positron is the antiparticle of an electron. This method uses positron annihilation lifetime to study the microstructure of materials, such as metal defects and phase transitions of various materials, as well as free electrons and solvated electrons in solutions.
Nuclear magnetic resonance method
The molecular structure of samples, especially the molecular structure of organic compounds, is determined by the NMR spectral characteristics such as chemical migration, coupling constant, multiplicity, width and intensity of absorption peak and temperature effect.
Compared with general analytical chemistry, radioanalytical chemistry has the following characteristics: based on the measurement of radioactivity or characteristic radiation, the analytical sensitivity is high (generally up to 1ppm), the accuracy is high, the analysis speed is fast, the method is simple and reliable, the sampling volume is small, and sometimes the sample structure can not be damaged.
Each analysis method has its own characteristics and the most suitable analysis range. Isotope dilution method should have known specific activity Radioactive standard , sub stoichiometric method does not need this; Neutron activation analysis is generally suitable for the analysis of medium and heavy elements and some light elements, and can analyze thick samples; Charged particle activation analysis and backscattering analysis are mainly used for surface analysis. Charged particle activation analysis is particularly suitable for light element analysis, while backscattering analysis is sensitive to medium and heavy elements. X-ray fluorescence analysis has good resolution and detection sensitivity. Generally, appropriate analysis methods are selected according to sample conditions and analysis requirements. No analytical method is comprehensive and appropriate, and sometimes it is necessary to select a combination of several methods to obtain satisfactory results. 
