PACS 29.30.Hs, 29.40.Vj, 29.40.Wk The common methods of neutron detection are reviewed with special attention paid to the application of cryogenics and semiconductors to the problem. The authors' work with LiF-and boron-based cryogenic instruments is described as well as the use of CdTe and HgI 2 for direct detection of neutrons. 1 Introduction Advances in materials and methods have enabled the detection of radiation by means today that would have seemed, to pioneers in the field a century ago, like science fiction. Improvements in technology have resulted, for gamma ray detection, in high-purity germanium operating at 77 K and providing 0.1% energy resolution above 1 MeV, more than an order of magnitude improvement over what was (and still is) achievable by scintillators. However, operating below 1 K, cryogenic calorimeters have been used in X-ray astronomy, in the search for dark matter, and more recently in gamma ray spectroscopy, and have achieved better than 70 eV resolution at 60 keV [1], a factor of 4 to 5 improvement over what can be achieved by germanium at that energy. Meanwhile, at the other end of the temperature spectrum, the development of new, wide band-gap semiconductors has sparked research in room temperature gamma ray detectors and has held out the hope of 1 -2% resolution and freedom from cryogenics [2,3].With such results being reported from the X-and gamma ray world it is natural to examine the possibilities for neutron detection. A cryogenic neutron detector would operate by detecting the heat pulses caused by neutron capture and scattering, while a semiconducting detector would detect the nuclear reaction products from a sensitizer (for example, fission fragments detected in a 235 U-coated Si diode) or from some constituent of the semiconductor.In the following sections, the common methods of neutron detection are described and their deficiencies with respect to neutron spectroscopy at energies above thermal (0.025 eV) are outlined. Published work on neutron-detecting cryogenic calorimeters will be reviewed and work by the present authors on boron-and lithium-based instruments will be discussed. Turning to semiconductors, we review work with coated and native (uncoated) semiconductor, including Cd 1-x Zn x Te (CZT) and HgI 2 , as applied to neutron detection. Results obtained by the authors with HgI 2 will be shown.

The Ag2Se/GeSe inorganic photoresist system has been used to produce submicron features by optical lithography. A practical process incorporating this material is the inorganic resist/polymer bilevel scheme. The successful printing of 0.5 μm lines and spaces is explained by the existence of an ’’edge sharpening’’ effect which accompanies the photo-doping process. Conventionally accepted limitations of photolithography are circumvented by the Ag2Se/GeSe resist, whose properties also include high contrast, resistance to O2 plasma, and high absorbance of UV light.

We describe our global optimization method called Stochastic Perturbation with Soft Constraints (SPSC), which uses information from known proteins to predict secondary structure, but not in the tertiary structure predictions or in generating the terms of the physics-based energy function. Our approach is also characterized by the use of an all atom energy function that includes a novel hydrophobic solvation function derived from experiments that shows promising ability for energy discrimination against misfolded structures. We present the results obtained using our SPSC method and energy function for blind prediction in the 4th Critical Assessment of Techniques for Protein Structure Prediction competition, and show that our approach is more effective on targets for which less information from known proteins is available. In fact our SPSC method produced the best prediction for one of the most difficult targets of the competition, a new fold protein of 240 amino acids.

We introduce a chemical sensing technology, named ChIMES (Chemical Identification through Magneto-Elastic Sensing), that can detect a broad range of targets and that has the capability of untethered communication through a metallic or nonmetallic barrier. These features enable many applications in which penetrations into the sampled environment are unwanted or infeasible because of health, safety, or environmental concerns, such as following the decomposition of a dangerous material in a sealed container. The sensing element is passive and consists of a target response material hard-coupled to a magnetoelastic wire. When the response material encounters a target, it expands, imposing mechanical stress on the wire and altering its magnetic permeability. Using a remote excitation-detection coil set, the changes in permeability are observed by switching the magnetic domains in the wire and measuring the modifications in the Faraday voltage as the stress is varied. Sensors with different response materials can be arrayed and interrogated individually. We describe the sensor and its associated instrumentation, compare the performance of several types of wire, and evaluate analytical metrics of single and arrayed ChIMES sensors against a suite of volatile organic compounds.

No abstract