Method for identifying and detecting iron electric melting beads in electric shock injury case

Abstract

The invention belongs to the technical field of forensic medicine, physical evidence inspection and criminal science, and discloses a method for identifying and detecting iron electric melting beads in electric shock cases, which comprises the following steps: S1, extracting a sample to be detected: extracting the sample from a suspected electric shock part by using a conductive adhesive sticking table; s2, primary screening with a scanning electron microscope: placing the extracted sample in a scanning electron microscope sample bin, and waiting for detection under the condition that the vacuum degree is less than 10 <-3 > Pa; identifying the metal particles by using an electron microscope back scattering probe in a back scattering mode; and S3, energy spectrum analysis: performing elemental component analysis on the identified metal particles by using an X-ray energy spectrometer, and screening the particles of which the iron content meets a preset condition. According to the method, the morphological judgment standard of the brain lines of the iron electric melting beads is provided, component analysis and morphological characteristics are closely combined, the problem of distinguishing iron electrode electric shock events from common iron particles in the environment is effectively solved, and more reliable binary evidence is provided for case qualification.

Description

Technical Field

[0001] This invention relates to the fields of forensic medicine, physical evidence examination and criminal science, and more specifically, to a method for identifying and detecting ferrous molten beads in cases of electric shock injuries. Background Technology

[0002] Electrical injuries are a common type of injury in forensic practice, involving both mechanical and thermal damage. In electrical incidents, when current passes through the human or animal body, characteristic tissue damage, known as current spots, often forms at the current entry and exit points. Due to the Joule heating effect and the high temperature of the electric arc, the current spot area is often accompanied by the vaporization, melting, and recondensation of the electrode metal, forming micron-sized molten metal beads. These beads are important microscopic evidence for determining the nature of an electrical injury and inferring the electrode material.

[0003] Currently, there are some standards and methods for the examination of current spots in the field of forensic science both domestically and internationally, such as the People's Republic of China Public Security Industry Standard GA / T 1939-2021 "Forensic Science Current Spot Examination: Scanning Electron Microscopy / X-ray Energy Dispersive Spectroscopy". This standard specifies general methods for morphological observation and elemental analysis of current spots using scanning electron microscopy and energy dispersive spectroscopy, but there are still significant shortcomings in practical applications.

[0004] 1. Lack of morphological description: Existing standards and common technical procedures focus on qualitative analysis of elemental composition, lacking a systematic and standardized description and classification of the morphological characteristics of fused beads. This results in identification results that rely on experience and lack repeatability and scientific rigor.

[0005] 2. Difficulty in characterizing iron electrode electric shock events: Existing methods lack specific identification features and criteria for judging molten iron beads formed by iron electrodes. Iron is ubiquitous in the environment, and distinguishing between characteristic molten iron beads formed by electric shock and iron particles introduced by environmental pollution is a key challenge in identification.

[0006] 3. Inconsistent testing procedures: The lack of unified and optimized operating procedures in sample extraction, instrument parameters, and data analysis thresholds leads to poor comparability of results from different laboratories and even different operators, affecting the authority of the identification conclusions.

[0007] Therefore, developing a system capable of systematically identifying ferrous fused beads, especially those with typical morphological characteristics, and establishing a standardized and operable detection process, is of great significance for improving the accuracy and scientific rigor of forensic identification in cases of electric shock injuries. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a method for identifying and detecting ferrous molten beads in cases of electric shock injuries.

[0009] To address the aforementioned technical problems, the present invention adopts the following technical solution: A method for identifying and detecting ferrous molten beads in cases of electric shock injuries includes the following steps: S1. Extracting the sample to be tested: Use a conductive adhesive extraction stage to extract the sample from the suspected electric shock site; S2. Scanning Electron Microscopy (SEM) Preliminary Screening: The extracted sample is placed in the SEM sample chamber under a vacuum of less than 10°C. -3 The object to be inspected is under Pa conditions; metal particles are identified using an electron microscope backscatter probe in backscatter mode. S3. Energy Spectroscopy Analysis: Elemental composition analysis of the identified metal particles is performed using an X-ray energy spectrometer to screen particles whose iron content meets the preset conditions. S4. Secondary electron imaging: Using a secondary electron probe to observe particle morphology characteristics under low accelerating voltage; S5. Blank control: Collect skin samples from non-electric shock sites as blank controls, and perform the above steps for testing and observation. S6. Result determination: If iron beads with brain pattern characteristics are found at the suspected site of electric shock, and no such beads are found in the blank control, then it is determined that an electric shock has occurred.

[0010] As a further aspect of the present invention: the method of using the conductive adhesive application platform is as follows: press firmly against the skin and repeatedly apply the adhesive 30 times until the conductive adhesive is no longer sticky; The conductive adhesive uses aluminum as a substrate and has a surface coated with viscous carbon powder.

[0011] As a further aspect of the present invention: the backscatter mode scanning conditions are as follows: the scanning electron microscope settings are: accelerating voltage 30kV, working distance 10mm, beam size 3.0, and backscatter CBS mode with brightness adjusted to 65% and contrast to 47%.

[0012] As a further aspect of the present invention, the particle screening conditions are: particle size greater than 2 μm, aspect ratio of 1 to 1.50, and Fe content of 50% to 100% after stripping C and O elements.

[0013] As a further aspect of the present invention, the secondary electron imaging conditions are: accelerating voltage 5kV, working distance 10mm, and beam spot size 3.0.

[0014] As a further aspect of the present invention: the brain texture features are: the particles are approximately round or spherical, and the surface has a continuous or discontinuous groove structure.

[0015] Compared with the prior art, the advantages of this invention are: I. This invention proposes a "brain pattern" morphological judgment standard for iron electrofused beads, which closely combines component analysis with morphological characteristics, effectively solving the problem of distinguishing iron electrode electric shock events from ordinary iron particles in the environment, and providing more reliable binary evidence for case characterization.

[0016] Second, this invention provides a complete set of standardized operating procedures from sampling number, instrument parameters, analysis thresholds to result determination, which greatly reduces human error and improves the comparability and repeatability of identification results between different laboratories.

[0017] Third, the equipment used in this invention (scanning electron microscope / X-ray energy dispersive spectroscopy) is widely used in forensic science laboratories. The method requires no complex pretreatment or special consumables, the detection cost is controllable, and it is easy to promote and apply in actual cases. The detection method is based on the physical principle of metal vaporization-condensation during electric shock, combined with the characteristic morphology summarized from a large number of experimental observations, and has a solid scientific theoretical foundation and practical support. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the morphology of brain-patterned ferro-fused beads in secondary electron mode of a scanning electron microscope, showing their near-spherical appearance and surface groove features. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Example 1 This embodiment provides a method for identifying and detecting ferrous molten beads in cases of electric shock injuries, including the following steps: I. Sample Extraction and Preparation: Using a conductive adhesive collection stage, apply appropriate pressure to the suspected site of electric shock on a human or animal (such as the palm, fingertips, or other areas where current spots are common), pressing firmly against the skin surface and repeating the collection process 30 times to ensure effective transfer of microscopic particles from the skin surface and superficial fissures to the conductive adhesive surface. After collection, place the sample in a clean acrylic protective sleeve and store and transport it at room temperature; no special treatment is required. Use tweezers to remove the sample during testing, avoiding contact with the conductive adhesive surface.

[0021] II. Initial screening and elemental analysis using scanning electron microscopy backscattering mode: The prepared sample is placed in the sample chamber of the scanning electron microscope, and a vacuum is drawn to the working vacuum level (usually below 10). -3The scanning electron microscope (SEM) operating parameters were set as follows: accelerating voltage 30 kV, working distance 10 mm, and electron beam spot diameter 3.0 mm. A backscattered electron probe was selected, and the image brightness and contrast were preset to 65% and 47%, respectively. Full-field or sectional scanning was performed in this mode. Backscattered electron imaging is sensitive to atomic number; metal particles (especially heavy metals) appear bright white and are easily identified from the biological tissue background.

[0022] X-ray energy dispersive spectroscopy (EDS) coupled with a scanning electron microscope (SEM) was used to analyze the elemental composition of irregularly shaped particles and metal particles. To accurately screen particles, particle identification conditions were set in the EDS analysis software: the equivalent diameter of the particles was greater than 2 μm (to ensure image clarity and morphological representativeness), and the aspect ratio of the particles was between 1 and 1.50 (to screen for approximately spherical particles). In the elemental determination conditions, carbon and oxygen were selected as either "stripped" or "ignored" because carbon often originates from conductive adhesives or contaminants, and oxygen is widely present in nature; their content fluctuates greatly and interferes with the determination of the core metal element. The iron content threshold was set to 50% to 100% (referring to the weight percentage of iron in the remaining elements after deducting C and O). Only particles meeting all the above conditions were recorded by the system as "candidate ferrous metal beads".

[0023] III. Morphological Observation and Feature Confirmation of Secondary Electron Patterns: For the "candidate ferrous molten beads" selected in the previous step, switch to secondary electron imaging mode for high-resolution morphology observation. Reduce the accelerating voltage of the scanning electron microscope to 5 kV, maintain the working distance at 10 mm, and set the beam size to 3.0. The low accelerating voltage reduces the penetration depth of the electron beam into the sample surface and the charge accumulation effect, resulting in clearer information on the surface topology.

[0024] The three-dimensional morphology of each candidate particle was carefully observed using a secondary electron probe, and manually verified to find iron molten beads that met the requirements. The magnification, brightness, contrast, and focal length were then adjusted appropriately to center the iron molten beads in the field of view. Typical iron molten beads formed by electric shock exhibit the following characteristics in secondary electron images: ① Overall shape: Approximately spherical or near-spherical; ② Surface characteristics: Its surface is not smooth, but is covered with irregular, continuous or discontinuous grooves and wrinkled structures, such as... Figure 1 As shown. This feature is named the "brain pattern" feature because its shape resembles the groove structure of the human cerebral cortex. This special morphology is believed to be a unique crystal or solidification morphology formed by the combined effects of surface tension, cooling rate, and substrate medium during the instantaneous cooling and solidification of molten iron on the skin surface (rich in moisture and organic matter).

[0025] IV. Blank control analysis and comprehensive judgment of results: Samples were extracted from the non-electric shock sites (blank areas) of the same individual in the same manner as blank controls. The blank control samples extracted from the non-electric shock sites were tested and analyzed strictly according to the same steps and parameters as described above.

[0026] The criteria for determining the results are as follows: If a certain number of particles are detected in a sample from a suspected electric shock site (based on the case background and statistical significance) that simultaneously meet the two conditions of "mainly iron (Fe>50%)" and "having a typical brain-like spherical morphology"; Furthermore, in the blank control samples, no iron particles with "brain pattern" characteristics were detected or only a very small amount (which can be regarded as background) were detected. This provides important microscopic morphological and compositional evidence that the test results support the claim that "the area was subjected to an electric shock from an iron electrode."

[0027] In addition, the above parameters are explained and based on the following: 1. Accelerating the switching between 30kV and 5kV voltages: 30kV can provide sufficient X-ray excitation efficiency for accurate energy spectrum composition analysis; 5kV can maximize surface morphology information and reduce electron beam penetration effect, which is the optimal condition for observing fine surface structures such as "brain texture".

[0028] 2. Removal of C and O elements: C and O are unavoidable elements in sample preparation (conductive adhesive) and biological samples. Their content is unstable. Direct use of full spectrum analysis will seriously interfere with the quantitative judgment of the main metal component (Fe). Analysis after removal can more accurately reflect the metallic nature of the particles.

[0029] 3. Scientific explanation of the "brain pattern" feature: During the electric shock, the instantaneous arc temperature can reach over 3000℃, which is enough to vaporize the iron in the contact material (electrode) (vaporization temperature is 2750℃). The vaporized iron cools down rapidly at the skin of the current spot and aggregates into spherical iron metal beads under the action of liquid surface tension. Because the morphology (crystal) of the iron metal beads is similar to the pattern of the human brain, it is named the "brain pattern" feature.

[0030] To further illustrate the application and verification of the method of the present invention in real cases, the following two experimental examples demonstrate the specific operation and judgment process of the method.

[0031] Experiment Example 1: Hand area detection in suspected electric shock injury cases Case background: A man was found unconscious next to a suspected electrified iron device, with suspicious pinpoint lesions on the skin of his palm.

[0032] Testing process: 1. Sample Extraction: Using a conductive adhesive collection station, samples were repeatedly pressed against the skin 30 times at suspected lesion points and the palm area on the left and right palms of the male, resulting in a total of 6 samples (P1-P6). At the same time, 2 blank control samples (C1-C2) were extracted from undamaged skin on his back.

[0033] 2. Instrumental analysis: All samples were placed in the same type of scanning electron microscope and scanned and screened using energy dispersive spectroscopy after setting the backscatter mode parameters according to step two of the above embodiment.

[0034] In palm samples P2 and P4, the system identified multiple candidate particles that met the criteria of "particle size > 2 μm, aspect ratio 1.2-1.4, and Fe content (after stripping C and O) 65%-92%".

[0035] Switching to the secondary electron mode (5kV) in step three to observe the particles, it was found that seven of the particles were clearly nearly spherical with a typical, irregular, meandering groove structure on the surface, i.e., "brain pattern" characteristics.

[0036] In the remaining palm samples and all blank control samples (C1-C2), although iron particles were occasionally detected, their morphology was mostly irregular flakes or angular, or although they were approximately spherical, their surfaces were smooth or only had simple depressions, and no typical "brain pattern" characteristics were found.

[0037] 3. Result Interpretation: Characteristic ferrous fusible beads were detected in the suspected electric shock area of ​​the palm, while no such beads were found in the control area. This result provides important microscopic evidence to support the conclusion that "the palm had come into contact with a charged iron object and suffered an electric shock injury."

[0038] Experiment Example 2: Animal Experiment Verification Experimental design: To verify the reliability of the method, a standardized electric shock device (iron electrode) was used to shock experimental animals (pigskin simulation) under controlled conditions to form current spots.

[0039] Testing process: 1. Sample extraction: Collect samples from the center and edges of the current spot formed by electric shock, and collect blank control samples from normal skin away from the current spot.

[0040] Instrumental analysis: The detection was carried out strictly in accordance with steps two and three of Example 1 above.

[0041] Experimental results: Iron spherical particles with "brain-like" characteristics were consistently detected in all electrocution spot samples, and the number detected showed a positive correlation with the electrocution energy. No such characteristic particles were detected in the blank control samples. This experiment systematically verified the effectiveness and specificity of the method of this invention in identifying molten iron beads originating from electrocution.

[0042] The method provided by this invention offers a scientific, reliable, and operable solution for the identification of ferrous electrolytic beads in cases of electric shock injuries through standardized procedures and clear characteristic criteria, significantly enhancing the probative value of forensic evidence in such cases.

[0043] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for identifying and detecting iron electric melting beads in an electric shock injury case, characterized in that: The method comprises the following steps: ​ S1, extracting a sample to be detected: using an electrically conductive adhesive to extract a sample from a suspected electric shock site; S2, Scanning Electron Microscope Preliminary Screening: The extracted sample is placed in the scanning electron microscope sample chamber, and the vacuum degree is less than 10 -3 Pa condition to be detected; in the backscattering mode, the metal particles are identified by using the electron microscope backscattering probe. S3, energy spectrum analysis: using an X-ray energy spectrometer to analyze the elemental composition of the identified metal particles, and screening particles with iron content meeting preset conditions; S4, secondary electron imaging: observing the morphological characteristics of the particles using a secondary electron probe under low acceleration voltage; S5, blank control: using an electrically conductive adhesive to extract skin from a non-electric shock site as a blank control, and detecting and observing according to the above steps; S6, result determination: if iron molten beads with brain texture characteristics are found in the suspected electric shock site, and no such molten beads are found in the blank control, it is determined that an electric shock has occurred.

2. The method of claim 1, wherein the method further comprises: determining the presence of iron in the sample by measuring the intensity of the iron emission line at 2,540.34 nm. The use method of the electrically conductive adhesive extraction platform is to press against the skin repeatedly for 30 times until the electrically conductive adhesive loses adhesion.

3. The method of claim 1, wherein the method further comprises: determining the presence of iron in the sample by measuring the intensity of the iron emission line at 2,540.34 nm. The electrically conductive adhesive uses aluminum as a base material, and the surface is coated with adhesive carbon powder.

4. The method of claim 1, wherein the method further comprises: determining the presence of iron in the sample. The backscattering mode scanning condition is: the scanning electron microscope setting condition is: acceleration voltage 30kV, working distance 10mm, beam spot size 3.0, backscattering CBS mode brightness adjustment 65% and contrast 47%.

5. The method of claim 1, wherein the method further comprises: determining the presence of iron in the sample. The particle screening condition is: particle size greater than 2μm, aspect ratio 1-1.50, and Fe content 50%-100% after stripping C and O elements.

6. The method of claim 1, wherein the method further comprises: identifying the iron-containing electrically fused bead in the electrocution case. The secondary electron imaging condition is: acceleration voltage 5kV, working distance 10mm, beam spot size 3.

0.

7. The method of claim 1, wherein the method further comprises: determining the presence of iron in the sample. The brain texture characteristics are: the particles are approximately circular or spherical, and the surface has continuous or discontinuous groove structure.

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