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X-ray Tube Type

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Do you ever get confused trying to differentiate between two X-ray tubes?

X-ray tubes are critical components you’ll find in an X-ray machine, and while their function is crucial to producing quality X-ray images, they often are of different types. Admittedly, the different types of X-ray tubes available in the industry today come with their merits and demerits. Nonetheless, they are usually employed for specific uses suitable for certain sample inspections. But here is the thing, identifying these different types of X-ray tubes can be challenging.

This post aims to help you identify between different X-ray tube types that are available to you whether you are looking to purchase one or not. So, if you are ready to know more, let’s dive in together.  


I. Types of X-ray Tube

X-ray tubes are the radiation production component in an X-ray machine, and they produce this radiation through a process known as thermionic emission. This process involves the release of electrons by applying an electric current, which generates the heat that releases the electrons. But these X-ray tubes come in different designs and capacities that enhance their radiation production abilities. Here are the different X-ray tube types available in the industry today. 


1. Open Type X-ray Tube

  • Definition – The open type X-ray tube is defined as one with its X-ray tube housing that can be opened, and its filament is often replaceable. To ensure the necessary vacuum environment in the housing, the open-type X-ray tube uses a two-staged pumping process every time the machine comes on. 
  • Material & Core Components – The core component for the open-type X-ray tube is the openable metallic housing, filament, anode, cathode, and stator. The material for the anode is usually tungsten which has high thermal resistivity because of the high heat energy generated during the operation of the X-ray machine. 
  • Assembly Method – Due to the interface of the metallic housing and the glass window of the housing and considering its ease of access, the open type X-ray tube is often assembled using the glass to metal assembly type. 
  • Feature – This X-ray tube features axis manipulation, X-ray flux control, field serviceability, and tube stability.  
  • Main advantage – The ability to open the X-ray tube housing allows easy access to the filament for maintenance operations, ensuring that the X-ray tube lasts for a long time. This benefit is the main advantage that the open X-ray tube offers. 


Open Type X-ray Tube


2. Sealed Type X-ray Tube

  • Definition – The sealed X-ray tube housing is wholly closed without access to the tube’s filament and other internal parts. This setup keeps the vacuum environment within the tube intact for instantly enhancing the electron production when you start the X-ray machine. However, the housing makes it impossible for field maintenance and filament replacement.  
  • Material & Core Components – The core components include a glass tube housing, filaments, anode, cathode, and stator. The tube material is mostly glass and other high thermal resistant materials like tungsten used for the anode.  
  • Assembly Method – While the sealed X-ray tube is made of glass, the assembly method used to achieve this setup is the hermetic method. The molten glass can wet the metals to form a tight bond which seals the vacuum securely. Also, the thermal expansion of the glass the metal used is often close to ensure the seal is intact during the cooling process. These two conditions are satisfied for the hermetic assembly method. 
  • Feature – The sealed X-ray tube features include high vacuum integrity, tube stability, and flux control.
  • Main advantage – The relatively cheap cost of the sealed X-ray tube is its main advantage over other types of X-ray tubes.  


Sealed Type X-ray Tube


3. Nano-focus X-ray Tube

  • Definition – This X-ray tube can develop electron beams that range from 0.1 micrometers to 0.5 micrometers. This X-ray tube is effective for analyzing very minute flaws and failures.
  • Material & Core Components – The nano-focus X-ray tube has two main components: a counting detector and a nanotube.
  • Assembly Method – It uses the hermetic method as the assembly method. 
  • Feature – The feature of this tube includes nano-focus range, narrower electron beams, sharp X-ray images. 
  • Main advantage – The main advantage of the nano-focus X-ray tube is the ability to produce very sharp X-ray images using a very narrow electron beam to identify tiny flaws that can cause failures. 


4. Micro-focus X-ray Tube

  • Definition – The micro-focus X-ray tube has a focal spot size below 100 micro-meter and can even be as low as five micrometers for advanced micro-focus X-ray tubes. 
  • Material & Core Components – The main components of this X-ray tube include anode materials of either Tin or gallium. 
  • Assembly Method -The assembly method for this X-ray tube is also the hermetic assembly method. 
  • Feature – Its features include negligible penumbra effect, high image resolution, accurate flaw identification, and reliable detection of minute flaws. 
  • Main advantage – Its main benefit is identifying very tiny defects within the sample material under examination. 


5. Mini-focus X-ray Tube

  • Definition – The mini-focus X-ray tube has a focal spot size below 1000 micrometer and can even be as low as 50 micrometers for advanced mini-focus X-ray tubes
  • Material & Core Components – Filament, rotor, stator, cathode, and anode.
  • Assembly Method – The assembly method for this X-ray tube is also the hermetic assembly method 
  • Feature – High resolution, radiation shield, compact and robust housing
  • Main advantage – Being able to identify very minute flaws within the test sample is its main advantage 


➤ Related Article: X-Ray Tube Parts

➤ Related Article: X-Ray Tube Working Principle And Its Construction


II. Comparison Guide: Open X-ray Tube v.s. Sealed X-ray Tube

When assessing the capability of your X-ray machine, one critical factor you may have to consider is the type of X-ray tube that will give you the required combination of voltage and amperage for a high-resolution X-ray image. Perhaps the most popular consideration in this field is using an open X-ray tube or a sealed X-ray tube. However, these two options of X-ray tubes have their pros and cons worth comparing. 

The open X-ray tube often produces X-ray images with good resolution, especially for low-density samples. Also, it can deliver high image magnification that is good for a more accurate inspection and failure analysis. Moreover, the cost of open X-ray tube source components is often high compared to that of sealed X-ray tubes. Using an open X-ray tube can include high image repeatability, high initial costs, and high system reliability. 

On the other hand, the sealed X-ray tubes present the following benefits: an optimized resolution for tightly arranged sample components and high image repeatability. Also, it has a low initial cost and a high level of system reliability.

Nonetheless, the sealed X-ray tubes are not without their cons. The demerits of this X-ray tube include low resolution when examining low-density materials and low magnification for accurate quality assessment. Lastly, the sealed X-ray tube often costs more when replacing its source components.  



In conclusion, knowing the different types of X-ray tubes available gives you the benefit of choosing the most suitable X-ray tube to meet your desired X-ray image quality and inspection result accuracy. Also, this knowledge can help you choose the most economical X-ray tube, both long term, and short term, as maintenance and replacement costs can also become significant over the years if you choose the wrong X-ray tube. However, identifying your inspection requirements, including material size, density, and geometry, will be the first step to selecting the right X-ray tube. 

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