Scientists at Lawrence Livermore National Laboratory have developed a plastic that can detect neutrons and distinguish them from gamma rays. The safe and inexpensive material could foster a range of new technologies in nuclear security and research.
Military and civilian nuclear scientists need tools to detect these types of radiation in their research, as do companies that develop devices to detect clandestine nuclear material. Plastic’s low cost could allow for the design of detection equipment large enough to use in facilities like ports and stadiums. Plastics that can detect the presence of both neutrons and gamma rays have long been available, but the materials’ inability to tell them apart limited their usefulness.
Existing technologies that can detect neutrons rely on difficult-to-grow organic crystals, hazardous liquids or a gaseous byproduct of tritium. Each poses challenges to widespread use.
The Livermore project created a scintillator – a material that emits light when exposed to ionizing radiation – from a polyvinyltoluene polymer matrix loaded with a scintillating dye, 2,5-diphenyloxazole. The resulting plastic can discriminate between neutrons and gamma rays, known as pulse shape discrimination.
"It has been established opinion since the 1950s that organic crystals and liquid scintillators can work for detecting neutrons, but that plastics are not suitable for neutron detection," LLNL materials scientist Natalia Zaitseva said in a lab release. "However, by studying mixed crystals and mixed liquids, we found that to achieve neutron discrimination from gamma rays, we had to increase the dye concentration in the plastics by at least ten-fold greater than would typically be used.”