U.S. physicists have successfully demonstrated a new method to detect radioactive materials from a distance using carbon-dioxide (CO₂) lasers. At the core of the new technique is a phenomenon called avalanche breakdown. This breakthrough has significant implications for national defense and emergency response, enabling rapid and accurate detection while maintaining a safe distance.
Science Behind the Technique
Avalanche Breakdown & Plasma Formation
- Radioactive decay releases charged particles that ionize the air, creating plasma (a state of matter with separated positive and negative charges).
- The electrons in this plasma can be accelerated to trigger avalanche breakdown, a chain reaction that releases more electrons.
What is Avalanche Breakdown?
- When radioactive materials decay, they release charged particles that ionize the surrounding air, i.e. separate its positive and negative charges and create a state of matter called plasma.
- Negative charges, or electrons, then can be accelerated to collide with other atoms and release even more electrons. This is avalanche breakdown.
Role of CO₂ Lasers
- The team used a CO₂ laser (9.2 µm wavelength) to accelerate these electrons, successfully detecting alpha particles from a radioactive source 10 meters away—10x farther than previous experiments.
- Laser-Induced Optical Backscatter: Accelerated “seed” electrons formed microplasma balls in the air. These microplasmas generated optical backscatter that was amplified through the laser system, significantly improving detection sensitivity.
- Advantages of Long-Wavelength Lasers: Facilitate electron avalanches, enabling detection of low concentrations of radioactive materials. Reduce unwanted ionization effects, preventing signal interference.
Potential Applications
This groundbreaking technique marks a significant step toward long-range remote sensing of radioactive materials, with potential applications in:
- National Security & Counterterrorism (detecting hidden radioactive threats)
- Nuclear Safety & Environmental Monitoring
- Emergency Response & Disaster Management