A tabletop neutron source

Is being used to calibrate a dark-matter detector. Expected to be the dominant type of matter in the universe, dark matter interacts only very weakly with normal matter. Like a neutrino detector, a dark-matter detector will succeed only if it has enough target atoms with enough mass, operates over an adequately long period, and has sufficient background suppression. In one prototype detector using both liquid and gaseous xenon, an incoming weakly interacting massive particle (WIMP) would strike a Xe nucleus and produce both scintillation light and free electrons from ionized Xe atoms, a process strikingly similar to elastic neutron-Xe interactions. Therefore, to calibrate the detector, physicists at Imperial College, London, aimed neutrons into the Xe bath using an inexpensive and compact plasma focus discharge device as a neutron source. Deuterium fusion reactions in a pinched plasma produced helium-3 nuclei plus forward-directed 2.45-MeV neutrons. The tabletop neutron source (a pulsed device...