Cosmic Rays Detect Nuclear Bomb Material

Experts at the Los Alamos National Laboratory (LANL) in New Mexico have created a new detector which can spot dense material, such as a block of radioactive plutonium or uranium possibly destined for a rogue weapons program, by noting how tiny elementary particles called muons pass through it.

Muons are castoffs of cosmic rays, created during interactions in the atmosphere. A typical muon can zip through almost anything, including you, a wall of lead, or about 33 feet (10 meters) of water.

“Cosmic rays are generated by unknown sources throughout the galaxy. They are high-energy, electrically charged particles. Cosmic rays are not part of the electromagnetic spectrum, which includes radio waves, visible light and X-rays.

"When cosmic rays enter Earth's atmosphere, traveling at nearly the speed of light, they collide with atoms and break up in a cascading shower of elementary particles, including muons.

"A muon is something like an electron but heavier. Unlike larger particles, such as protons, muons are not made out of smaller building blocks. When they travel through matter, muons do lose energy, however. As muons pass through very dense material, they scatter at notably different angles than when passing through steel, plastic or other less dense substances.

"The signature we detect is some number of cosmic-ray muons, all intersecting in a common volume, that scatter to a significantly larger angle than is expected for normal objects,” describes Christopher Morris, who helped invent the apparatus in research led by Konstantin Borozdin, an LANL astrophysicist, of how the device operates – adding that the device is not a terrorist bomb detect all.

"It cannot distinguish between different high atomic weight materials. Gold looks the same as uranium.  Further, the device is not sensitive to common explosives.  And while a version could be constructed to monitor moving vehicles, the present approach requires the target to sit still for about half a minute,” points out Morris about the limitations of the device which is still much better than the current methods used to detect illegal nuclear material.