Monthly Archives: November 2014

Useful selfies

Last blog about the risks of radiation concluded that X-rays aren’t that dangerous to deal with in industrial applications, at least with sources that can be turned off.

Back in the day when Roentgen first researched the properties of these waves no one knew what kind of nasty stuff they could cause to human tissue and people started to mess around with them before any of it could really get documented. As is inevitable with any visual recording technology, people started taking selfies with it and pretty soon the medical benefits were recognized, may it be at the human cost of people getting severe radiation burns, dermatitis and later on, cancer.

Stuff got pretty out of hand, even shoe stores started using X-rays in so called ‘shoe-fitting fluoroscopes’ intended to see if peoples toes sat snugly in their shoes.

fluoroscope 2

So this technology got exposed to the public before all of its aspects were fully understood with simultaneous beneficial and horrendous results. When governmental scientists discover new technologies that could have a grand impact on humanity there is sometimes debate on whether or not they should release their findings to the world. The people have the right to know, but simultaneously people might start misusing it. The same debate acted up some time ago about the findings on how to manipulate certain influenza strains because some people were of the opinion that it was a ‘cookbook recipe’ for terrorists to make unbeatable bio-weapons. Others were of the opinion that the research could help in combating future pandemics and other unexpected beneficial applications.

What’s your take on this? Keep stuff secret and prevent misuse or let everyone know and see what happens, or some other way to regulate this stuff?

Acoustic emission

The video added to this post shows a part of the Philae spacecraft that descended onto a comet earlier this week. At around 2:30 into the video, it shows us the important part for this post: the SESAME research part.

Sesame is a great example of the practical applications for acoustic emission as a non destructive test method.

Each landing foot of Philae has acoustic emitters and receivers. Each of the legs will take turns transmitting acoustic waves (100 Hertz to KiloHertz range) into the comet which the sensors of the other legs will measure. How that wave is attenuated, that is, weakened and transformed, by the cometary material it passes through, can be used along with other cometary properties gained from Philae instruments, to determine daily and seasonal variations in the comet’s structure to a depth of about 2 meters.

To clarify this and explain acoustic emission: an emitter produces sound waves which get reflected or absorbed by the object we’re testing. The reflected waves are captured by the receivers and based on these patterns, it’s possible to reconstruct the object, determine the material and properties of the object or even detect small cracks and other imperfections in the object.

This last application, detection of imperfections, is often used for rods or ball bearings to trace fatigue before the component fails and could cause damage to other components of the machine.

Do you see other useful applications for this technique? Leave it in the comments.

Radiation Hazard


So we’re working with an industrial CT-Scanner which uses “harmful” X-rays. Harmful because X-rays belong to the spectrum of electromagnetic waves that have ionizing effects, which have devastating consequences on organic tissue. Logically at first we weren’t too comfortable around all those radiation hazard signs. But we took some time to educate ourselves.

ray Turns out in industrial applications the use of these harmfull ionizing waves doesn’t really matter. Clearing up a common misconception first;

After an object is scanned there is no residual radiation left within the object or the source. Applied to daily life: our irradiated food or scanned luggage at the airport/metro hold no risk of any health dangers due to radiation.

Induction of radiation in materials is possible but requires a high critical threshold that is only reached when exposed to very high levels of X- or gamma rays. On top of that, induced radiation usually has a very short decay half-life.

Food and objects from the area around the Fukushima power plant disaster are potentially dangerous because they could be contaminated with airborne radioactive particles that originated from the plant site.

Irradiated food is a controversial topic, but this is mainly due to the discussion of creating ‘free radicals’ and killing the naturally present ‘healthy’ bacteria within foodstuffs. ( If you want more information on why food irradiation is applied please read the text on this page [Dutch] : ).

The active sources in these machines do however hold radiation poisoning risks, but it’s ‘easy’ to protect the machine operators by placing thick (lead) shields around the testing chamber that absorb all emitted waves and placing sensors or ‘dosimeters’ around the operational area and on the staff. There’s even development going on to create dosimeters that can be attached to your smartphone

Scanners used for medical purposes and ‘body scanners’ used in some airports do hold some controversial radiation health dangers, but that’s a topic for a next blog.

So after reading all this, what’s your take on non-medical uses of X-rays? Still weary of touching your bag after passing customs in the airport? And afraid your apple might grow some legs after irradiation? Post your thoughts.

Non destructive testing: a short introduction

The CT-scanner we’re improving is a relatively new method of non-destructive testing, but what is non-destructive testing exactly? describes non-destructive testing as follows:

Non-destructive testing is a descriptive term used for the examination of materials and components in such a way that allows materials to be examined without changing or destroying their usefulness. NDT or NDE can be used to find, size and locate surface and subsurface flaws and defects.

The description shows us that NDT is a range of interesting methods to detect and fix defects, without causing more problems or destruction. It’s most often used for weld verification or structural mechanics, but these methods are also extremely useful for parts produced by additive manufacturing.

Some of the most common methods are:

  • Acoustic emission testing
  • Visual inspection
  • Electromagnetic testing
  • Dye penetrant testing
  • Ultrasonic inspection
  • Leak detection
  • Radiographic testing

A more complete list can be found here

What methods do you think are interesting to explain further and can you think of some real life applications of these techniques ?