Neutron Radiography

Carbonite Freezing the Fun and Easy Way with Neutron Imaging

By August 31, 2020September 1st, 2020No Comments
The Han Solo action figure used in our neutron imaging experiment

And by “braving wretched hives of scum and villainy and making deals with bounty hunters across the galaxy,” we mean “asking his coworkers if anyone had a Han Solo action figure he could shoot neutrons at.”

After our engineers buried a plastic toy in a jar of staples to show how easily neutrons penetrate metals (but not plastic) and demonstrate the weird ways neutrons interact with materials, marketing director Katie Rittenhouse, who had volunteered one of her kids’ less-favorite toys for the experiment (don’t worry, the toy is fine), commented that it bore no small resemblance to the fate of a certain scruffy-looking nerf herder a long, long time ago, in a galaxy far, far away. And this put our engineers, or at least one of them, in the mood to try out a more accurate reenactment—with neutron imaging!

Our engineering intern Nick Anderson, who worked on neutron imaging at the Phoenix Neutron Imaging Center from May through August as part of our summer internship program, took the initiative to get his hands on this Han Solo action figure, braving wretched hives of scum and villainy and making deals with bounty hunters across the galaxy to get his hands on the notorious scoundrel.

Unfortunately, we don’t have a carbonite freezing facility like Cloud City’s at PNIC, but we have something almost as good—an aluminum box and lead pellets—that we can use to create a tableau worthy of Jabba the Hutt’s palace. Denser, heavier elements such as lead and other metals are of little interest to neutrons, but hydrogen-rich compounds like plastic stop them in their tracks, which makes neutron imaging an extremely useful tool for detecting the presence of certain hydrogen-rich smugglers encased in a thick sheet of impenetrable carbonite lead.

Note: This isn’t the first brush Phoenix has had with the Star Wars universe:

The “Carbonite Freezing” Process

The aluminum box, partially filled with lead pellets and partially covering the Han Solo action figure
The aluminum box, fully filled with lead pellets and completely covering the Han Solo action figure
The aluminum box containing lead pellets and the hidden Han Solo action figure

As the aluminum box was filled and sealed, the faint mournful howl of a Wookiee could be heard in the distance

So far, it doesn’t look so impressive compared to a nightmarish portrait of frozen anguish, but that’s where neutron imaging comes in. Neutron imaging works almost exactly the same way X-ray imaging does, except with neutron radiation instead of X-rays. In fact, much of the same technology, albeit heavily modified, is used in the imaging process. Our imaging system actually uses an X-ray detector outfitted with a conversion screen that allows it to create an image from the neutrons which pass through the detector.

Nick not only performed the imaging of Han Solo’s cold, metallic prison, but also rigged our lead-filled box onto a turntable and used it to take images at multiple angles similar to how we would create a 3D image using neutron computed tomography, resulting in a GIF worthy of an intergalactic crime lord’s trophy cabinet.

Unfortunately for Jabba, the dashing rogue defiantly struck a dynamic action pose the instant before he was “frozen.”


Your first thought if you’d been tasked with finding the special prize hidden in this box might have been to simply X-ray it. Here’s why that wouldn’t work:

X-rays, as you can see, tend to have a very difficult time penetrating aluminum or lead even at high energies. To take this X-ray image, we had our imaging system cranked up to 425 kilovolts and were still unable to penetrate the aluminum and lead—and even if they could have, the X-rays would have blown right through the plastic without capturing anything on film as well.

neutron xray cross section chartX-rays are known to pass easily through less dense materials and less easily through more dense materials, which is why your teeth show up on the X-rays you get once per year at the dentist’s office but your skin and lips don’t. This is because X-rays, which are electromagnetic waves, interact with an atom’s electron cloud, and the bigger an atom’s electron cloud is, the denser it is, and the more difficulty X-rays have passing through it.

Neutrons don’t follow such a linear pattern. The only part of the atom they interact with are the extremely small nucleus, which is mind-bogglingly tiny compared to the electron cloud surrounding it. Because the ways neutrons interact with atomic nuclei are governed by a completely different set of rules, there is no easy-to-describe linear relationship between a material’s density and its transparency to neutrons. For example, some dense materials, like aluminum and lead, are very translucent, but not all of them; and some light materials, especially plastics and water, are very opaque; and here and there you have elements like boron and gadolinium that buck trends by being extremely opaque regardless of density altogether!

From Dungeons and Dragons to Neutrons and Nuclei

Summer engineering intern Nick Anderson and his "side project" at PNIC

Nick Anderson: Claims not to be an intergalactic bounty hunter, but there’s no hiding the cold glee in his eyes as he poses with his captive quarry.

Nick Anderson, the man behind this image, started his engineering internship at Phoenix back in May while pursuing his undergraduate degree in nuclear engineering at the University of Wisconsin – Madison. He had always been interested in the imaging and nondestructive testing aspect of materials sciences, and so working for Phoenix was a no-brainer. What made accepting an internship position at Phoenix an even easier choice was the commute! Being a nuclear technology company right in the backyard of UW-Madison and one of the best and most well-known nuclear engineering programs in the Midwest has its advantages—Phoenix is never too far away from a treasure trove of amazing, young, talented people who are passionate about nuclear technology, and all those amazing people are never too far away from us. In fact, Phoenix was founded by and is filled with alumni of UW-Madison’s undergraduate and postgrad nuclear programs!

Nick found out about Phoenix, and later about our internship program, through friends he made in his studies: he and a few other people in his program—some of whom happened to work for Phoenix at PNIC and later became his coworkers—played together in a DnD group. One thing led to another, and when we officially started up our internship program, Nick had his foot in the door. It can’t be understated how valuable networking is to finding a great job and starting a great career, and networking can happen in the unlikeliest of places—you never know if you’ll find the next step in your career at your university’s job fair or in a den of hobgoblins.

Life at Phoenix

When Nick came aboard, his job was to learn, and there’s no better teacher than experience—especially with passionate coworkers to act as mentors. One of Phoenix’s three summer interns, Nick was tasked with learning to work the neutron imaging system at PNIC under the mentorship of Phoenix’s seasoned engineers such as Benjamin Johnson, who showed him how to set up the system and work the software, and Michael Taylor (a member of the ASTM neutron imaging committee working to set global quality standards for neutron radiography as a method of nondestructive testing), who brought him up to speed on the fundamentals of radiographic testing and the math behind the science. As important as it is to learn in a classroom setting, hands-on learning and mastery tends to be a lot more effective—and more fun!

To describe working at Phoenix in one word—it’s awesome. For every day of my internship from the beginning of May to the end of August, I went into work every morning to meet passionate, driven, hardworking people and left work feeling fulfilled—there was never a day where I felt like I hadn’t done anything important or invigorating. Not a single day ever felt wasted or boring. So many jobs out there can so easily feel like pointless drudgery sometimes (or most of the time), but jobs at Phoenix, especially in engineering where all the cool stuff is happening, aren’t like that at all.

Nick AndersonEngineering intern at PNIC

While Nick’s internship came to an end with August and he’s now focusing on completing his undergraduate studies, he and Phoenix haven’t parted ways just yet. We’ll be providing him with resources for his senior project, and when he’s finished at UW-Madison, both he and we are hopeful that we can bring him on as a full-time engineer!

Learn more about careers at Phoenix