For the first time, a team of scientists at Lawrence Livermore National Laboratory (LLNL) has developed a plastic material which enables to detect nuclear substances such as plutonium and uranium.
According to LLNL, the team developed a new plastic material capable of efficiently distinguishing neutrons from gamma rays, something not thought possible before.
This material, described in the journal Nuclear Instruments and Methods in Physics Research A, could assist in detecting nuclear substances that might be used in improvised nuclear devices by terrorists and could help in detecting neutrons in major scientific projects.
“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,” said Dr. Natalia Zaitseva, lead author and LLNL materials scientist.
A scintillator is a special material, which lights up when excited by ionizing radiation.
“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,” Dr. Zaitseva explained.
“Efficient pulse shape discrimination (between neutrons and gamma rays) combined with easy fabrication and advantages in deployment of plastics over liquids may lead to widespread use of new pulse shape discrimination materials as large-volume and low-cost neutron detectors,” the scientists wrote in their paper.
“In some ways it is a particularly good time to develop a new method for detecting neutrons, given the advantages and drawbacks of current methods,” said fellow LLNL materials scientist Dr. Stephen Payne.
Plastics have more flexibility in their composition and structure than crystals, as well as having none of the hazards associated with liquid scintillators.
The team demonstrated a plastic scintillator that can discriminate between neutrons and gamma rays with a polyvinyltoluene polymer matrix loaded with a scintillating dye, 2,5-diphenyloxazole.
They found that plastic scintillators have a roughly 20 percent finer resolution for neutron-gamma ray discrimination than liquid scintillators.
Along with discovering plastic scintillators with efficient neutron-gamma ray discrimination, the team also has found that this discrimination can be very sensitive to certain impurities in crystals.
“When we started this work, there was little understanding of how pulse shape discrimination was affected by the chemical composition of the scintillating materials. We have found some of the major principles of molecular interaction that determine the presence or absence of pulse shape discrimination properties in organic scintillators,” Dr. Zaitseva said.
“We’re very good at inventing technologies, but we need commercial partners to bring our innovations to market,” concluded Dr. Payne.