Why do we build medical scanners from sunken battleships?

By Matthew Allen

Countless ships were sunk during the first and second World Wars. Many of them remain untouched at the bottom of the ocean; however, some of these ships have since been stripped of their steel, to be used in building medical and physics equipment. It’s not because there’s a shortage of steel, but because this steel has a very unique property that modern steel doesn’t have. But, what is it that makes the steel of sunken battleships so special?

Why do we use steel from battleships like this to make medical equipment? (PD-US, https://en.wikipedia.org/w/index.php?curid=11211751)

This week I was fortunate to have a short tour of some of the latest cutting-edge medical equipment at Cardiff’s University Hospital of Wales. Some of these machines cost millions of pounds and are equipped with the latest, most sensitive scanners and detectors. They are designed to look very modern and as welcoming as possible to patients. However, in one room was a very old machine, made of a thick steel shell, which is used to measure radiation to diagnose patients. My guide then said something which fascinated me – “The steel casing of the machine comes from an old World War 2 battleship”! Why on Earth would a hospital have a medical scanner built from old ships and why is the steel used to build this scanner so special?

Well, let’s start at the beginning – how steel is made. Steel is a widely used metal which is made from iron; it is considered better than iron, due to it being stronger and less brittle.The process to make steel is pretty simple. Iron ore, which is mined from the ground, contains a lot of impurities and carbon, which act to make the iron weaker. To remove these unwanted materials, the Iron is heated up in a blast furnace until it becomes molten, before limestone is added to the mixture. The limestone floats on top of the molten iron and draws out the impurities and some of the excess carbon from the iron mixture. Air from the atmosphere is used in the process to help remove impurities from the iron ore. These impurities are then drained away, leaving iron with a small, controlled amount of carbon in it, which we call steel. This process worked great for hundreds of years, until the 16th of July 1945 at 5:26 am. From that moment on, steel making and the world as a whole changed forever, because this was the first detonation of an atomic bomb.

An image of Trinity, the first every nuclear weapon detonated

An image of Trinity, the first every nuclear weapon detonated (By Jack Aeby – http://www.mbe.doe.gov/me70/manhattan/trinity_photograph.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=38385597)

The trinity test, as it was known, was the first detonation of an atomic bomb and was shortly followed by the detonation of the two bombs at Hiroshima and Nagasaki which ended the second World War. Many people think that these were the only atomic weapons ever detonated; however, there have been around 1,900 atomic weapons test since the end of second World War. With each of these explosions, radiation and radioactive material was released in to the world and has slowly built up over time.

So, let’s imagine that today you wanted to build an incredibly sensitive radiation detector, such as a Geiger counter or a medical radiation scanner. To get the most accurate readings you have to make sure none of the components inside the detector are themselves radioactive, otherwise your detector will be less sensitive, and this is where our problem with modern created steel comes from. Because we pass air through iron to make steel, any radioactive particles in the air which are leftover from the nearly two thousand nuclear detonations over the years will become part of the steel. This makes all modern day steel, made using atmospheric air, slightly radioactive. This steel can’t be used in any type of sensitive radiation detector, including medical scanners, such as the one in the hospital that I visited.

The Tirpitz, a german ship which since being sunk has been stripped of it’s low-background steel (By Daventry B J (Flt Lt), Royal Air Force official photographer – http://media.iwm.org.uk/iwm/mediaLib//54/media-54740/large.jpgThis is photograph CL 2830 from the collections of the Imperial War Museums., Public Domain, https://commons.wikimedia.org/w/index.php?curid=24455379)

How do we get around this? Well, we have to use steel that was made before the first ever atomic detonation, also known as low-background steel. This means, we can only use steel that was made before the 16th of July 1945. Any steel made after this day has a chance of containing radioactive particles, splitting the history of steel in to two very distinct periods. However, back in 1945, most produced steel went in to making ships and tanks for the war effort. This makes sunken ships, which lay untouched under the ocean, one of the only reliable sources of non-radioactive steel. Being under the water has also protected the steel from being directly exposed to any radiation, as water is a very good blocker of radioactive particles and energy. As a result, when we need to make medical or physics equipment out of steel which needs to be very sensitive to radiation, we often have to use steel from sunken battleships.

Thankfully, modern techniques allow us to make steel without including the radioactive impurities of the air. However, this process is very expensive, so the pre-war steel is still often used. The amount of low-background steel that exists is obviously limited by the amount which we can get from sunken ships, making it a valuable and very limited resource, so one day we will have to make all our steel the difficult and expensive way.

So, the next time you’re using a hospital scanner, a Geiger counter or some other kind of sensitive radiation detector, just remember that parts of it could be made from battleships which were sunk over 70 years ago!

About the Blogger – Matthew Allen

Matthew is an astrophysicist who has been working at space made simple since 2016. He has a passion for technology, including Virtual and Augmented reality, statistics and astronomy.


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Posted in Engineering, Physics