Thermal explosions imaged with table-top X-ray radiography

Because so-called secondary high explosives are relatively insensitive, they’re less likely to accidentally detonate, making them advantageous for uses like demolishing a building or launching a rocket. But researchers still don’t have a full understanding of their explosive behavior — crucial for proper handling and emergency response in an accident.

In Applied Physics Letters, researchers from Los Alamos National Laboratory demonstrate a new technique that uses a table-top X-ray machine to produce images of these explosions in action. They revealed the details for why one secondary high explosive shredded its aluminum container, another merely bent it, and a third didn’t explode but burned slowly like a candle.

Explosives are usually detonated inside metal casings and thus the explosions are opaque. To directly study a blast, researchers have had to use proton and X-ray radiography to penetrate the case and explosive materials. Denser material blocks more protons or X-rays, producing shadow images that reveal details of the explosion. But these conventional methods require dedicated, expensive facilities.

When the researchers learned the density of the explosion is comparable to that of bone, they realized they could also make images using the smaller and cheaper medical X-ray machines doctors use. Unlike with dedicated facilities, where the X-ray has to be turned on simultaneously with the explosion — whose timing is often uncertain — table-top machines can be kept on until the blast occurs.

The group used their radiography to image the combustion process, revealing the inner material evolution as solid turned to gas. Their investigation of two important classes of explosives, called TATB and HMX, revealed detailed propagation behavior of the internal combustion and the differences between them.

Source: “Internal sub-sonic burning during an explosion viewed via dynamic X-ray radiography,” by L. Smilowitz, B. F. Henson, D. Oschwald, N. Suvorova, and D. Remelius, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.5004424 .