Elimination of ghosting artifacts from wavelength-shifting fiber neutron detectors.

Misassignment of neutron position (ghosting) produces artifacts which have been observed in wavelength-shifting (WLS) fiber detectors developed for time-of-flight (TOF) neutron powder diffraction. In position-sensitive detectors (PSDs) with WLS fiber encoding, thermal and cold neutrons interact with a monolithic (6)LiF/ZnS:Ag scintillator screen, and scintillation photons are generated and transported through the crossed fibers to photomultipliers (PMTs). The neutron position is determined by photon counts in the PMTs within a preset time window. Ghosting occurs when neutrons hit the group boundaries of two neighboring PMTs for x-position multiplexing, which is modeled as resulting from a long travel length (about 3-5 mm) of a small number of scintillation photons. This model is supported by the change observed in aperture images when the threshold number for photon-pulses was adjusted for neutron event determination. When the threshold number of photon-pulses was set above 10 for each PMT, the ghost peaks in the aperture images and TOF spectra of powder diffraction were strongly suppressed or completely eliminated, and the intrinsic background levels of the WLS detectors were significantly reduced. Our result indicates that WLS fiber detector is a promising alternative for (3)He PSDs for neutron scattering.

Telesensor integrated circuits.

Progress in personal computing has recently permitted small research programs to design and simulate application-specific integrated circuits (ASICs). Inexpensive fabrication of silicon chips can then be obtained using chip foundries, and quite complex circuits can be greatly reduced in size with an accompanying increase in certain performance characteristics. Within the past 5 years it has also become possible to design ASICs which can transmit and receive radio signals and which thus may be employed in applications in which wired connections for input and output of signals are not practicable. We are currently developing research-grade prototype ASICs for the monitoring of human vital signs. In this case one or more sensors placed on an ASIC provides a signal to be transmitted a distance of 2-3 meters to a receiver/display unit. The use of ASIC telesensors provides the possibility of wireless monitoring, including long-term monitoring, with inexpensive and unencumbering devices. Their self-contained nature permits a number of potential uses in future biomedical applications as new sensors are devised which are amenable to deployment on silicon.