Tungsten Additive Manufacturing: X-Rays Collimators

Collimators are devices used to orientate and filtrate a beam of particles or waves. This article gives an in-depth presentation of additive manufacturing of collimators, current technologies and future challenges. We will also review the additive manufacturing of tungsten.

Electromagnetic radiation

An electromagnetic radiation is a way to transfer energy without any physical medium, as opposed to sound waves for example. 

 

Many different types of EM radiation exist, all parts of the EM spectrum shown in the image below. 

The electromagnetic spectrum

Electromagnetic (EM) wave

The energy of an EM wave can be quantified using its wavelength, expressed in nanometers (nm). The lower the wavelength, the higher the energy of the wave. 

 

Typically, visible light radiation is within 400 nm and 800 nm, below are UV light, X-rays and gamma rays. Those last two types of radiation are the one we will focus on today. You can learn more about EM radiation on this Radio2space detailed article

 

In additive manufacturing of metals, including tungsten additive manufacturing, an infrared  (IR) laser source is used to melt the metallic powder and fuse the layers together as we will explain later on. 

Collimators in the Industry

As explained earlier, collimators are devices used to orientate and filtrate a beam of particles or waves. Their working principle is quite easy as shown in the figure below.

An X-ray collimator schematic work – Beamler

 

When a diffuse source of EM radiation needs to be orientated and/or narrowed, for example to create an image on a detector, a collimator is a simple and efficient solution. However, as explained in the previous paragraph, the lower the wavelength the higher the energy meaning the X and gamma rays are the most energetic EM waves.

 

This creates different problems such as septal penetration, which occurs when a given high energy beam crosses a septum of the collimator. This induces a misplaced signal on the detector.

 

To avoid this problem, high atomic numbers and dense materials need to be used and tungsten is an excellent potential candidate.

However, since tungsten is a very hard material, it is difficult to manufacture using traditional machining techniques.

 

Tungsten also has the highest fusion temperature of all materials so a tungsten part cannot be produced using casting for example. Usually, tungsten collimators are manufactured using tungsten sheets making the process difficult.

 

All those challenges make additive manufacturing of tungsten an excellent choice for producing collimators.

EM radiations in the Industry

Many industries have found an important application in the use of EM radiation, especially X-rays and gamma rays. Beginning with nuclear physics and medicine.

 

X-rays are used in computed tomography (CT) to obtain a 3D-scan of a patient’s body, but also in science to obtain a 3D scan of small parts. The image below illustrates computed tomography for medicine.

CT scan allows to make cross section images of a patient’s body – Lompoc Valley Medical Center

 

In materials science, energy dispersive X-rays (EDX) detectors also use collimators to orientate the X-rays emitted by a sample in a SEM (scanning electron microscope).   Gamma rays on the other hand are more energetic but still found an important application in living tissues imaging. Gamma rays are classified in energy classes and lower energy rays can be easily stopped by a detector to form an image but still manage to penetrate tissues, as explained in this ScienceDirect’s topic.

Tungsten additive manufacturing of Collimators

Tungsten additive manufacturing is achieved using Selective Laser Melting (SLM) technology. An infrared laser is used to melt the metallic powder and fuse the layers together.

 

An article was published by Sidambe et al. to demonstrate the feasibility of additive manufacturing of tungsten for collimators application. A pinhole collimator was printed using a 1070 nm IR laser and an energy density of 348 J/mm3.

 

The wavelength of the IR laser can be adapted to the printed material, as explained in this article on the additive manufacturing of copper.

 

The image below shows the final 3D printed tungsten part with SEM images of the surface microstructure.

Pinhole tungsten collimator – Sidambe et al. – IJRMHM

 

The resulting microstructure without any post-treatment is visible on the SEM images of the figure above. Thanks to tailored build parameters such as laser energy density, high relative density of final tungsten printed parts can be achieved, up to 98% the density of pure tungsten (19.2 g.cm-3).

Potential of AM for Collimators

Most types of collimators can also be produced using additive manufacturing of tungsten, for imaging with gamma rays for example. The image below shows a fanbeam collimator, courtesy of NuclearFields.

Fanbeam collimator – NuclearFields

 

As explained in their article “When viewed from one direction, the holes are parallel. When viewed from the other direction, the holes converge”. This complex and fine design could easily be manufactured using tungsten additive manufacturing.

Conclusion

It was demonstrated in the literature that high density 3D printed tungsten parts can be produced for collimators application. Additive manufacturing of tungsten is a mature technology that enables the production of high value parts for a fraction of the cost of traditional manufacturing techniques.

 

If you are looking for a high density refractory material such as tungsten for a prototype or series production, contact Beamler and request a quote to dive into your project now !

Contact Beamler now to receive your Tungsten quote

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