That causes the boron atom to break (fission) into two reaction products: a lithium-7 ( 7Li) ion and an alpha particle made up of two protons and two neutrons. The 7Li ion and alpha particle fly off in opposite directions and, upon escaping from the target, deposit up to 2.5 million electron volts of kinetic energy into the surrounding xenon gas, exciting some of the atoms. First an incoming neutron strikes an atom of boron-10. The detection process has several stages. At the center of the cell is a neutron target, or "converter," consisting of carbon foam coated with a boron-carbon compound containing some boron-10 ( 10B, the isotope notable for its ability to capture neutrons). The cell has a window to admit incoming neutrons and an attached photomultiplier tube that captures and amplifies faint UV light signals. The apparatus consists of a hollow cube 7 cm on a side that is filled with xenon gas. Fortunately, one way they can be detected is when they prompt a fission reaction and the reaction products interact with a surrounding noble gas."įor several years, Clark and colleagues at NIST's Physical Measurement Laboratory, the University of Maryland, and the Johns Hopkins Applied Physics Laboratory (APL) have been investigating such a method that relies on ultraviolet light emitted from atoms of xenon or other noble gases in response to by-products of a nuclear reaction between an incident neutron and an atom of boron. You can't accelerate them, and they don't generally have enough energy to excite anything. "Neutrons are, of course, electrically neutral. "Detection of low-energy neutrons is called 'the dismal science' by many of its practitioners for good reason," says Charles Clark of NIST's Quantum Measurement Division. That shortage has prompted a worldwide search for another method or material to fill the gap. As production of these weapons has declined over the past three decades, so has the inventory of tritium – and hence 3He. Historically, the sole source of 3He has been the radioactive decay of tritium, a key component in nuclear weapons. Since 9/11, demand for detectors has risen dramatically.Ĭonventional detectors rely on a Geiger counter-like cylinder filled with Helium-3 ( 3He), a rare isotope that exhibits a distinctive reaction when struck by a neutron. The excited atoms shed their energy as ultraviolet radiation, which registers in a light-amplifying device, signaling the arrival of the neutron.īuilding on work reported in 2014, which showed that a process called "excimer scintillation" provides a mechanism for sensitive neutron detection, the new results reveal that a specially treated carbon foam with high surface area may hold particular promise as a critical component in the next generation of detectors.ĭetecting neutrons emitted by radioactive materials is of critical importance to homeland security and counter-terrorism activities, such as screening cargo containers and identifying "dirty bomb" materials, as well as other vital applications in nuclear power instrumentation, workplace safety, industry, and science. When an incoming neutron hits a boron atom, the atom splits into pieces which travel into the xenon gas, exciting the atoms there. The animation shows how neutrons are detected by a novel device in which a boron-coated carbon foam sits in a chamber filled with xenon gas. Neutron detection by excimer scintillation
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |