Abstract: An activation detector for fast-neutrons has a yttrium target exposed to a neutron source. Fast-neutrons which have energy in excess of 1 MeV (above a threshold energy level) generate gamma rays from a nuclear reaction with the yttrium, the gamma rays having an energy level of 908.96 keV, and the resultant gamma rays are coupled to a scintillator which generates an optical response, the optical response of the scintillator is coupled to a photomultiplier tube which generates an electrical response. The number of counts from the photomultiplier tube provides an accurate indication of the fast-neutron flux, and the detector is exclusively sensitive to fast-neutrons with an energy level over 1 MeV, thereby providing a fast-neutron detector which does not require calibration or the setting of a threshold.

Abstract: Structures of microminiature dimensions are formed by scanning a nearly parallel beam of high energy light ions across the surface of a resist material such as PMMA in a predetermined pattern. The resulting chemical changes in the exposed resist material allows a chemical developer to remove the exposed material while leaving the unexposed material substantially unaffected. In addition because the ions have a well defined range in the material depending on their energy, the resist can be exposed to a predetermined well defined depth. By this method, resist structures of three dimensional complexity can be micromachined. This is achieved by simultaneously scanning the beam and orienting the resist layer in a controlled manner. Further enhancement may be achieved by the use of multiple deposition and exposure of resist layers. These resist microstructures may be further utilized to produce microstructures in other materials by the application of processes such as electroplating and micromoulding.