The basic composition and structure of X-ray fluorescence spectrometer

X-ray fluorescence spectrometer is an instrument used to determine the type and content of elements in a substance. Everyone knows that a substance is composed of elements. The atomic energy level structure of each element is specific, and the characteristic X-ray energy generated during the transition is also Fixed (the energy difference between the electron shells of the two orbitals). Therefore, by measuring the energy of the characteristic X-ray, the corresponding element can be determined, and the strength of the characteristic X-ray represents the content of the element.

Based on the above principles, the core structure of the X-ray fluorescence spectrometer is an excitation source and a detector. Among them, the excitation source is a component that generates characteristic X-rays from the excitation element. The commonly used excitation source is electromagnetic radiation excitation. The detector is to convert the energy and intensity of X-ray fluorescence into a certain shape and number of electrical pulses. In essence, it is an energy → electricity sensor. Commonly used detectors have a proportional counter and flicker. Counter and semiconductor counter.

Because X-rays have a certain wavelength and a certain amount of energy, there are two basic types of X-ray fluorescence spectrometers: wavelength dispersion type and energy dispersion type. Let's take a detailed look at the structure of X-ray fluorescence spectrometer.

1. X-ray tube

X-ray fluorescence spectrometer requires X-ray tube as excitation light source. The primary X-ray produced by the X-ray tube serves as a radiation source for exciting X-ray fluorescence. Only when the wavelength of the primary X-ray is slightly shorter than the absorption limit of the excited element lmin, can the X-ray fluorescence be effectively excited.

The target of the X-ray tube and the working voltage of the tube determine the intensity of the primary X-ray that can effectively excite the excited element. As the working voltage of the tube increases, the main decision for the viscosity is the increase in the proportion of the tight short-wave X-rays at one time, so the intensity of the fluorescent X-rays generated also increases. The X-rays generated by the X-ray tube are incident on the sample through the beryllium window to excite the characteristic X-rays of the sample elements. During normal operation, about 0.2% of the power consumed by the X-ray tube is converted into X-ray radiation, and the rest is converted into heat The X-ray tube is heated, so the target electrode must be continuously cooled with cooling water.

2. Spectroscopic system

The main component of the spectroscopic system is the crystal beam splitter. Its function is to separate X-rays of different wavelengths through crystal diffraction. The spectroscopic crystal is driven by a crystal rotating mechanism. Because the position of the sample is fixed, in order to detect fluorescent X-rays with a wavelength of λ, the spectroscopic crystal is rotated by an angle of θ, and the detector must be rotated by an angle of 2θ. Current X-ray fluorescence spectrometers are equipped with crystals with different interplanar spacings to analyze elements in different ranges.

3. Inspection and recording system

The detectors used in X-ray fluorescence spectrometers include a gas flow proportional counter and a scintillation counter. It is mainly composed of a metal cylinder anode and a core wire anode. The cylinder is filled with a mixture of argon (90%) and methane (10%). X-rays are injected into the tube to ionize Ar atoms, and the generated Ar + moves toward the cathode In addition, it causes the ionization of other Ar atoms, and the result of avalanche ionization produces a pulse signal whose pulse amplitude is proportional to the X-ray energy. Therefore, this kind of counter is called a proportional counter. In order to ensure that the concentration of the gas in the counter remains unchanged, the gas keeps flowing. The gas flow proportional counter is suitable for the detection of light elements.

The above is a detailed introduction of the basic structure of X-ray fluorescence spectrometer, for your reference, I hope to help you!