In recent years, the security inspection of baggage items entering key locations has become a standard practice worldwide. With the growing concerns about aviation and public safety, X-ray technology has evolved rapidly and is now widely used in security screening. This article explores the fundamental principles of X-ray safety inspection techniques and discusses common methods employed in the field.
Terrorist attacks around the globe have made public security a top priority for governments. To combat rising threats, many countries have enhanced security measures at critical sites like airports, train stations, and ports. These measures focus on detecting dangerous items such as explosives and drugs. However, the diversity of explosive materials and their varying forms make it challenging to detect them effectively. As a result, there is a growing need for more advanced and accurate detection technologies.
Currently, international research into detecting contraband focuses on several methods, including X-ray detection, neutron detection, electromagnetic measurement, and vapor particle detection. Among these, X-ray technology stands out due to its maturity and wide application. It includes techniques like X-ray transmission, dual-energy X-ray detection, X-ray scattering, and X-ray computed tomography (CT). These methods analyze physical characteristics of objects to identify prohibited items.
One of the key parameters extracted from X-ray scans is the effective atomic number (Zeff) and density (Ï) of the object. These values help determine the material type. However, existing security inspection methods still have limitations. Combining different techniques and implementing multi-level inspections are common strategies to improve accuracy and reduce false alarms.
**Principle of X-ray Security Inspection**
X-rays are a form of high-energy electromagnetic radiation produced when high-speed electrons decelerate or when electrons transition between energy levels in atoms. Due to their strong penetrating power, they can pass through luggage and other objects, making them ideal for security screening.
Once generated, X-rays are directed through a collimator to create a fan-shaped beam that illuminates the object being inspected. As the X-rays interact with the object, some are absorbed while others are scattered. The intensity of the transmitted X-rays varies depending on the material's properties. Detectors capture this variation, converting the X-ray energy into electrical signals. These signals are then processed by a computer to generate images that help identify potential threats.
**Common X-ray Safety Inspection Techniques**
The single-energy X-ray method uses the difference in X-ray attenuation to distinguish materials. While it provides clear images of high-Z materials like metals, it struggles to detect hidden explosives behind dense substances.
The dual-energy X-ray technique improves upon this by using two different X-ray energies to measure the ratio of attenuation. This allows for the determination of the effective atomic number, helping to differentiate organic and inorganic materials. Although it enhances detection accuracy, it still faces challenges in distinguishing between allowed and prohibited organic materials.
The X-ray backscattering method is particularly useful for detecting items hidden on the surface or in dark compartments. By capturing Compton scattering signals, it offers better visibility of low-Z materials, such as plastic explosives. This method has been applied to vehicle inspections, where traditional X-ray systems may miss concealed items behind thick metal layers.
Despite its advantages, X-ray backscattering cannot simultaneously determine Zeff and density, limiting its ability to detect internal threats. Combining dual-energy and backscattering technologies can provide more detailed information, improving detection accuracy and reducing false positives. These integrated approaches are now widely used in container, vehicle, and human body inspections.
**Conclusion**
While various X-ray detection technologies are extensively used in security screening, no single system can fully provide both effective atomic number and density data. Each method has its strengths and limitations. Therefore, the integration of multiple technologies and the implementation of multi-level inspections are essential for the future development of security equipment.
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