Principle of the hottest dispersion X-ray fluoresc

Principle of dispersive X-ray fluorescence spectrometer

when energy is often faulty: when high-energy X-rays with a quantity higher than the binding energy of electrons in the inner layer of the atom collide with the atom after the sample is broken, an inner electron is expelled and a hole appears, so that the whole atomic system is in an unstable excited state. The lifetime of the excited atom is about (10) -12- (10) -14s, and then spontaneously transitions from the state of high energy to the state of low energy This process is called galloping process The relaxation process can be either nonradiative or radiative When the electrons in the outer layer transition to the hole, the released energy is immediately absorbed inside the atom and drives out another secondary photoelectron in the outer layer. The type IV sample is used to determine the Poisson's ratio of the above two kinds of FRP. This is called Auger effect, also known as secondary photoelectric effect or non radiation effect. The driven secondary photoelectron is called Auger electron

its energy is characteristic and independent of the energy of incident radiation When the energy released by the outer electrons jumping into the inner hole is not absorbed in the atom, but emitted in the form of radiation, X-ray fluorescence is generated, and its energy is equal to the energy difference between the two energy levels Therefore, the energy or wavelength of X-ray fluorescence is characteristic and has a one-to-one correspondence with elements After the k-layer electrons are expelled, their holes can be filled by any electron in the outer layer, which can produce a series of spectral lines, called k-family spectral lines: the X-ray from the L-layer to the k-layer radiation is called k-ray, and the X-ray from the m-layer to the k-layer radiation is called k-ray

similarly, the expulsion of L-layer electrons can produce L-Series radiation If the incident X-ray excites the k-layer electrons of an element into photo electrons, then the L-layer electrons transition to the k-layer. At this time, the energy E is released, and e=ek-el. This energy is released in the form of X-rays, which is k-rays. It can also produce k-rays, L-Series rays, etc Seley found that the wavelength of fluorescent X-rays is related to the atomic

ordinal number Z of elements, and its mathematical relationship is as follows: =k (Z-S) -2, which is Mosley's law, where K and s are constants. Therefore, as long as the wavelength of fluorescent X-rays is measured, the species of elements can be known, which is the basis of qualitative analysis of fluorescent X-rays In addition, there is a certain relationship between the intensity of fluorescent X-ray and the content of corresponding elements. Therefore, quantitative analysis of elements can be carried out

x-ray generation

X-ray tube is used to apply high voltage to accelerate electrons to collide with metal anode (cathode) to produce X-rays In terms of design, there are two kinds of X-ray tubes: side window type and end window type, both of which are designed to irradiate X-rays evenly on the surface of samples

beryllium foil is generally used for X-ray windows Cathode (also known as target material) is mostly tungsten (W), rhodium (RH), molybdenum (MO), chromium (CR7). Pay attention to the movement of the machine, handle it with care, and pay attention to packaging and shock resistance during transportation.) And other materials The use of these targets is based on the analysis of different elements and the use of different materials In principle, it is analyzed that the material of the target element is different from that of the target material

how to use fluorescent X-ray for quantitative analysis

in the sample containing a certain element 1, irradiation of X-ray once will produce fluorescent X-ray of element 1, but the intensity of fluorescent X-ray at this time will change with the content of element a in the sample If the content of element 1 is high, the intensity of fluorescent X-rays will become stronger Note this. If the fluorescence X-ray intensity of the sample with known concentration is known in advance, the content of element a in the sample can be calculated

there are three methods for quantitative analysis by fluorescent X-ray One is the method of making measuring lines (empirical coefficient method) This method is to determine several actual samples with known concentration, and the operation process depends entirely on the operator's operation level. If you want to determine the relationship between the fluorescent X-ray intensity and concentration of elements, determine unknown samples based on the results, and obtain fluorescent X-rays, so as to obtain the concentration value

another method is the basic parameter method of theoretical calculus (FP method) On the premise of fully understanding the composition of the sample and the types of elements, this method uses the theoretical value of the calculated fluorescence X-ray intensity to infer that the composition of the fluorescence X-ray intensity of each element of the unknown sample is consistent

nbs-gsc method is also called theoretical alpha coefficient method Based on the basic principle of fluorescence X-ray excitation, it theoretically uses basic physical parameters to calculate the primary and secondary characteristic X-ray fluorescence intensity of each element in the sample Based on this, Lachance comprehensive correction coefficients are calculated, and then these theoretical coefficients are used to correct the absorption enhancement effect between elements It is different from the empirical coefficient method. These correction coefficients are obtained from theory rather than experience Therefore, it does not need so many standard samples, as long as a few standard samples to calibrate the instrument factor