scattering; polycapillary X-ray half optics; energy dispersive X-ray scattering; molecules

Energy dispersive X-ray scattering (EDXRS) technique is an effective method for identification of sorts of liquids. In this experiment, the polycapillary X(-ray half optics is used to replace the slits of the EDXRS to identify the sorts of the liquid samples. The experinental results show that alignment system consisting of the two polycapillary X-ray half optics can improve the efficiency of X-ray source and the resolution of the scattering spectrum. The EDXRS with polycapillary X-ray half optics is an appropriate method to identify the sorts and concentrations of liquids, and has a widely applications for the identification of sorts of liquids.

Energy dispersive X-ray scattering (EDXRS) has been widely used in the study of liquid species identification. Diffraction or scattering occurs when molecules or ions in the liquid interact with the incident X-ray, and the diffraction or scattering signals of molecules or ions can be detected within a small angle range, so as to obtain the internal information of the molecular structure of the liquid and determine the type of liquid identification. Yu et al. established an energy dispersive X-ray scattering device and carried out research on the identification of liquid substances, and achieved a series of progress.

However, the analysis of energy dispersive X-ray scattering requires the use of multiple sets of slits to collimate the incident X-ray beam. At the same time, in order to ensure good angular resolution of the measurement results, it is necessary to add a set of slits in front of the X-ray detector. Collimation of diffracted or scattered X-ray beams. Although the alignment of multiple groups of slits in the device ensures the accuracy of the measurement results, it also causes a large amount of X-ray loss.

Since the 1980s, a variety of X-ray focusing and collimating optical devices have been developed, including diffractive Fresnel zone plates, reflective Krikpatrick-Baez (K-B) mirrors, refractive compound refractive lenses, etc.) The device mainly obtains monochromatic X-rays or narrow-band X-rays, and is rarely used in the research of multi-band X-ray EDXRS.

The capillary X-ray lens is a focused X-ray optical device developed in the 1990s based on the principle of total reflection, which realizes the regulation of broadband X-rays and greatly improves the utilization efficiency of X-rays. It transmits the X-ray beam emitted from the point light source in the way of total reflection on the inner wall of the hollow capillary glass tube, and then uses the bending of the hollow glass tube to focus the X-ray beam into a focal spot with a diameter of tens of microns, and makes the X-ray beam The strength is increased by 2 to 3 orders of magnitude. In the same way, the capillary half mirror can use total reflection to collimate the X-ray beam excited by the point light source into an X-ray beam with a small divergence for X-ray diffraction or scattering analysis; in addition, the capillary half mirror uses total reflection.

The X-ray beam with a small divergence or parallel is converged into a point in a way that can be measured by an X-ray energy spectrum detector with a small area window, which can shorten the distance between the incident X-ray and the sample or between the diffracted X-ray and the detector. The distance can improve the utilization efficiency of X-rays. Therefore, this paper attempts to use a capillary X-ray half-mirror to collimate the X-rays excited by the X-ray tube of the point light source into an X-ray beam of small divergence to irradiate the liquid sample, and at the same time collect the X-rays with a small-area window energy spectrum X-ray detector. The X-ray diffraction or scattering signal collected by the capillary half-lens is used to identify and study the type of liquid.

The energy dispersive X-ray scattering experiments were carried out on the small-angle scattering device equipped with the Rigaku D/MAX X-ray diffractometer. The experimental device consists of 50kV high-voltage power supply, 2kW Mo target X-ray tube (point light source, light spot 1mm×1mm), capillary half-lens A (front focal length ƒ₁=100.7mm, length L₁=53.5mm, and outer diameter of the entrance end R₁=6.4mm , the outer diameter of the outlet end R₂=7mm), the polycapillary semi-lens B (length L₂=47.6mm, the outer diameter of the inlet end R₃=7mm, the outer diameter of the outlet end R₄=6.4mm), the XR-100SDD X-ray detection of the American Amptek company It consists of an analyzer (the active area of the window is 25mm², and the energy resolution for Mn-Kα is 125eV), a PX5 multi-channel analyzer and a corner system. The X-rays excited from the point light source X-ray tube are condensed into a small divergence X-ray beam by the capillary half mirror A and then irradiated on the sample. The diameter of the X-ray irradiated sample is about 4 mm. The X-ray diffracted or scattered from the liquid sample is condensed by the capillary half-lens B into an X-ray beam with a diameter of less than 1mm, which is detected by the XR-100SDDX ray detector. The stepper motor drives the X-ray detector to rotate with the sample as the center, and the rotation angle accuracy is 0.01°. The overall schematic diagram of the energy dispersive X-ray scattering device is shown in Figure 1.

Fig.1 Energy dispersive X-ray scattering device with polycapillary X-ray half optics

The relationship between the scattered X-ray wavelength λ, the scattering angle θ and the momentum transfer q of the scattering parameter is:

where
h and c are Planck’s constant and the speed of light, and
E is the energy of scattered photons.
When the unit of E is expressed in keV, the unit of q is nm^-1. The main factors affecting the momentum transfer q of the scattering parameter are the energy of the X-ray irradiating the sample and the size of the diffraction angle θ of the probe X-ray. The X-ray energy irradiated on the sample is determined by the voltage of the X-ray tube and the transmission efficiency of the capillary half-lens A (the capillary X-ray lens has a higher transmission efficiency for X-rays with an energy of 2~12keV, and a higher transmission efficiency for high-energy X-rays. Low transmission efficiency; and the X-ray diffraction angle θ is determined by the angle of the X-ray detector and the distance from the capillary half-lens B to the sample (the capillary half-lens B mainly collects X-rays that meet total reflection on the inner wall of the capillary or directly pass through the hollow capillary. ray, the distance from the capillary half-lens B to the sample is different, and the angles of the X-rays of the same energy incident on the capillary half-lens B are different).

Therefore, under the condition that the X-ray tube voltage is 50kV, the current is 2mA, and the detection time is 90s, use a pipette to accurately measure 10ml of acetone reagent and load it into a polypropylene (PP) test tube for direct testing to explore X-ray The detection angle of the detector and the detection distance from the X-ray detector to the sample. Place the X-ray detector at a distance of 20cm from the liquid sample, and detect the X-rays of acetone at angles of 0.5°, 1°, 2°, 3°, 4°, 5°, and 6° with the human X-ray beam, respectively. The energy dispersive X-ray scattering spectrum of acetone with the same detection distance but different angles by the X-ray detector is obtained, as shown in Figure 2(a). In addition, the X-ray detector was placed under the condition of the same scattering angle of 1°, and the energy dispersive X-ray scattering spectra of the acetone samples were measured at the distances between the X-ray detector and the sample at 20, 50, 100, 150, and 200 cm. As shown in Fig. 2(b).

Fig.2 Energy dispersive X-ray scattering spectra of acetone at different angles and positions. (a)Energy dispersive X-ray scattering spectra of acetone at different angles in the same position;(b) energy dispersive X-ray scattering spectra of acetone at different positions in the same angle

Fig.3 Effect of Mo absorption on the energy dispersive X-ray scattering spectra of acetone

As can be seen from Figure 2, the energy dispersive X-ray scattering spectrum of the capillary X-ray lens of the liquid sample has two scattering peaks, which is obviously different from the energy dispersive X-ray scattering spectrum using slit collimation, but it improves the The accuracy of liquid sample type identification is improved. Since the X-ray transmission efficiency of the capillary X-ray lens for different energies is different, the intensity and energy distribution of the X-ray energy spectrum of the incident sample are changed. If a metal Mo absorber with a thickness of 64 μm is placed in front of the sample to absorb the low-energy X-rays incident on the sample, the energy dispersive X-ray scattering spectrum of the acetone sample with and without the Mo absorber is measured. (See Figure 3). As can be seen from Figure 3, after the low-energy X-rays incident on the sample were absorbed by the Mo absorption sheet, the intensity of the first scattering peak of the energy dispersive X-ray scattering spectrum of the acetone sample increased, but the intensity of the second scattering peak decreased , almost close to the background, the measured X-ray scattering spectrum is close to the traditional X-ray scattering spectrum using slit collimation, which reduces the resolution of the scattering energy spectrum. Therefore, the scattering of liquid energy dispersive X-rays by the capillary X-ray lens can generate two scattering peaks that meet the experimental requirements, and can improve the identification ability and identification accuracy of liquid samples. Due to the good collimation of the collimation system composed of two capillary half-lenses, the counts of the X-ray detectors decrease significantly when the scattering angle is less than 4° (see Fig. 2(a)).

From the experimental results in Figure 2, it can be seen that the X-ray detector can obtain the scattering energy spectrum of the acetone sample that meets the experimental requirements at the position of the scattering angle of 1° and the distance from the sample of 20 cm. Therefore, the X-ray detector was chosen to carry out the following identification studies of the liquid samples under the conditions of a scattering angle of 1° and a distance of 20 cm from the sample.

Using the experimental device, five different kinds of liquid samples, such as ethanol aqueous solution (25%, 50%, 75%, 100%), 65% HNO₃, 40% HF, 30% H₂O₂ (volume fraction) solution and deionized H₂O, were tested respectively. Identify research. Accurately measure 10ml of the above-mentioned reagent with a pipette, load it in a PP material test tube, the voltage of the X-ray tube is 50kV, the current is 2mA, the detection time of the X-ray detector is 90s, the scattering angle is 1°, and the X-ray detection The measurement was carried out under the condition that the distance between the detector and the sample was 20 cm. The energy dispersive X-ray scattering spectra of ethanol aqueous solutions at different volume fractions were measured, as shown in Fig. 4(a). The energy dispersive X-ray scattering spectra of the four liquid samples, HNO₃, HF, H₂O₂, and H₂O, are shown in Fig. 4(b).

Fig.4 Energy dispersive X-ray scattering spectra of different kinds of liquid samples. (a) Energy dispersive X-ray scattering spectra of ethanol solution in different concentrations;(b)energy dispersive X-ray scattering spectra of HNO3, HF, H2O2,H2O

It can be seen from Figure 4 that the energy dispersive X-ray scattering spectra of the ethanol solution and the acid solution with different volume fractions of the two capillary X-ray half-lenses are quite different, and it is easy to identify the liquid type and content from the scattering spectra.

However, the energy dispersive X-ray scattering peaks of ethanol solutions with different volume fractions shift to the direction of low energy with the increase of the solution volume fraction; while the X-ray scattering peaks of H₂O₂, HF, HNO₃; these three liquid samples are shifted to high energy. move in the direction. Among them, H₂O and HF have the same molecular weight, but their energy scattering spectra are obviously different.

The shift of the X-ray scattering peaks of liquid substances of different types and contents is related to the molecular structure inside the liquid, and the scattering ability of the incident photons is different due to the difference in the strength of the atomic or molecular chemical bonds in the liquid substance. When the chemical bond strength of the molecule is large, the nuclei of the bonded atoms have a strong binding ability to the electrons outside the nucleus.

At this time, the collision between the incident photon and the electron outside the nucleus is similar to the collision with the whole particle, and the energy loss of the incident photon is small; on the contrary, when the chemical bond when the intensity is small, the energy loss of incident photons after collision is large. For example, when comparing HNO₃, HF, and H₂O reagents, there are many types of chemical bonds in HNO₃ reagents, such as ionic bonds formed by H⁺, NO₃^– ions, water molecules or NO₃^–, covalent bonds within ions, intermolecular water or NO₃^– Internal hydrogen bonds of ions, etc.; the chemical bonds existing in HF reagents include internal covalent bonds of HF molecules or water molecules, intermolecular hydrogen bonds, partial electrolytic ionic bonds, etc.; in water, there are only internal covalent bonds of water molecules and intermolecular hydrogen bonds, Some ionic bonds, etc.

A comprehensive comparison of chemical bond types and bond energies shows that the chemical bond strength in water is small, that is, the water molecule has a small binding ability to internal electrons, which may cause the H₂O molecule to interact with incident photons more obviously, and the X-ray scattering peak position is shifted to the direction of low energy. On the contrary, the scattering peaks of X-ray scattering spectra such as HNO₃ shift to the direction of high energy.

An energy dispersive X-ray scattering device collimated by a capillary half-lens was used in the experiment to identify and study the types of liquids. The experimental results show that the capillary half-lens can completely replace the collimating slit in the traditional energy dispersive X-ray scattering device, and can effectively improve the utilization efficiency of X-rays. In the experiment, a 100W power X-ray source (50kV, 2mA) and an energy spectral X-ray detector with a 25mm² small area window were used to realize the identification of liquid species by energy dispersive X-ray scattering, and to improve the resolution of the liquid scattering energy spectrum. (There are two scattering energy peaks in the X-ray scattering spectrum). If this device is used, combined with multivariate statistical data processing methods such as factor analysis, to establish an energy dispersive X-ray scattering database of various liquid substances, it is entirely possible to realize the rapid identification and detection of liquid samples of different contents and types. and content identification has a wide range of application prospects.