Why is tungsten used in x ray tubes?

As a core component in medical imaging, industrial non-destructive testing, scientific research and analysis, the performance of X-ray tubes directly determines the imaging quality, working stability and service life of the equipment. The selection of core materials is a key link in the design and manufacture of X-ray tubes. Among the many metal materials that can be used for the core components of X-ray tubes, tungsten has become the first choice for mainstream manufacturers around the world due to its unique physical and chemical properties. As an enterprise deeply involved in tungsten products for more than 10 years, FANMETAL's technicians have combined their experience to analyse the logic behind the use of tungsten in X-ray tubes.

The Core Requirements For An X-Ray Tube

The working process of the X-ray tube is: the cathode filament heats and emits thermal electrons, which accelerate under the action of a high-voltage electric field and hit the anode target at extremely high speed, generating X-rays through conjugate radiation and characteristic radiation. In this process, the anode target and cathode filament need to withstand extreme working conditions, so strict requirements are put forward for the material:

• High temperature resistance: When electrons hit the anode, more than 99% of the energy will be converted into thermal energy, the instantaneous temperature of the target surface can exceed 2000°C, and the long-term operating temperature needs to be maintained above 1000°C.
• High atomic number: The higher the atomic number, the greater the probability of electrons colliding with nuclei, the higher the X-ray yield, and the shorter and stronger the penetration of X-rays generated, which can meet the needs of different scenarios (such as industrial thick parts inspection, medical CT).
• Good thermal conductivity: it is necessary to quickly export a large amount of heat generated by the target surface, reduce local temperature accumulation, extend the service life of components, and avoid cracking due to thermal stress.
• Stable physical and chemical properties: In high vacuum and strong electric field environments, it needs to have excellent anti-oxidation and sputtering properties, and not react with other components in the tube to ensure long-term stable operation of the X-ray tube.
• Adaptable processing performance and cost-effectiveness: It needs to be able to make complex shapes (such as rotating anode target discs, spiral filaments) through precision machining, while taking into account production costs, suitable for large-scale applications.

Tungsten Target X Ray Tube Compared to Other Metal Materials

At present, the materials that can be tried to be applied to the core components of X-ray tubes are mainly divided into two categories: one is the metal materials used for anode targets and cathode filaments, including copper, molybdenum, rhenium, tantalum, gold, etc. and some alloys; Another category is the material used for X-ray exit windows, with beryllium (beryllium window) being the most commonly used core material. The two work together to support the normal operation of the X-ray tube.

Function of the Tungsten Target In X Ray Tube

• Efficient generation of rays: Undertake the high-speed thermal electrons emitted by the cathode filament, and efficiently generate X-rays through the conjugate radiation (electron deceleration to release energy) and characteristic radiation (electron transition in the inner layer of tungsten atoms), which is the core prerequisite for X-ray tubes to achieve imaging and detection functions. The tungsten x ray target we produce can improve the X-ray yield by more than 15% compared to ordinary targets by optimising the grain structure, ensuring clear imaging and accurate detection.
• Withstand extreme high temperature: more than 99% of the energy is converted into heat energy when the electron hits the target, and the instantaneous temperature of the target surface can reach more than 2000 °C, and the tungsten target can stably withstand the impact of extreme high temperature with a high melting point of 3410 °C, avoid melting, deformation or volatilization, prevent the X-ray tube from stopping due to target damage, and provide a guarantee for the long-term continuous operation of the equipment.
• X-ray quality control: Tungsten has an atomic number of up to 74, which can control the wavelength and intensity of X-rays through its own atomic structure - it can not only generate continuous spectrum X-rays (suitable for detection objects of different densities and thicknesses), but also emit high-intensity characteristic X-rays (suitable for high-precision detection scenarios), while reducing unnecessary ray losses, taking into account imaging quality and radiation safety.
• Support equipment stability: Tungsten targets have stable chemical properties in high vacuum and strong electric field environments, and are not easy to oxidise or sputter, which can avoid the target particles falling off and polluting the environment in the tube (such as damaging the beryllium window and affecting the vacuum level).

How To Make Tungsten More Suitable For X-Ray Tubes

1. In the raw material screening process, we only select virgin tungsten concentrate with a purity of≥ 99.95%, and control the impurity content in tungsten below 0.005% through multiple impurity removal processes to avoid impurities affecting the high temperature resistance and stability of tungsten.
2. In process development, we optimised our exclusive processing for X-ray tube components. For anode tungsten targets, we use the "composite target moulding process" to combine tungsten with molybdenum, utilising tungsten's high temperature resistance and atomic number, and molybdenum's thermal conductivity, to reduce target surface temperature. For cathodic filaments, we improved drawing and annealing processes to enhance their toughness and high-temperature strength, preventing burnout.
3. We are equipped with metallographic microscopes, hardness testers, high-temperature performance testers and other equipment to strictly test tungsten products from multiple dimensions to ensure that the product performance meets the standard. At present, the pass rate of tungsten products for X-ray tubes is 99.98%, which is widely recognised by customers.
4. For example, the tungsten rhenium alloy target we have developed combines the cost performance of tungsten and the high temperature stability of rhenium, adapting to the needs of high-power and long-life X-ray tubes, and has been applied to special X-ray inspection equipment in the aerospace field.

Summary and Reflection

Although the budget cost of the entire product will be high with the current increase in the price of tungsten raw materials, tungsten is still the only metal material that can fully meet the stringent requirements of X-ray tubes.
--Its extremely high melting point solves the problem of component loss under extremely high temperature conditions of X-ray tubes, the high atomic number realises the X-ray emission requirements of the whole scenario, the good comprehensive performance balances the efficiency and service life of the equipment, and the reasonable processing performance and cost performance support the large-scale development of the industry

For more than ten years, FANMETAL has continued to focus on the research, development and production of non-ferrous metal products, especially from the processing of basic tungsten products to the provision of high-end customised solutions. If you have any questions about this product's details or pricing inquiries, don't hesitate to get in touch with us at admin@fanmetalloy.com. We look forward to your message.