@article{hawari_gidley_moxom_hathaway_mukherjee_2011, title={Operation and testing of the PULSTAR reactor intense slow positron beam and PALS spectrometers}, volume={262}, ISBN={["*****************"]}, ISSN={["1742-6588"]}, DOI={10.1088/1742-6596/262/1/012024}, abstractNote={An intense slow positron beam has been established at the 1-MW PULSTAR nuclear reactor. The beam is operational generating mono-energetic positrons with an energy of 1-keV. The maximum measured intensity slightly exceeds 109 e+/s. The beam is operated routinely with an intensity of approximately 5×108 e+/s. The positrons are generated through gamma-ray pair production interactions in two back-to-back banks of tungsten converter/moderators. The gamma-rays are produced in the PULSTAR core and by thermal neutron capture in a cadmium shroud that surrounds the tungsten. The primary utilization of the PULSTAR positron beam is the characterization of nanoscale structure in materials. Consequently, the beam has been equipped with two state-of-the-art PALS spectrometers. The first spectrometer is dedicated to measurements in materials such as metals and semiconductors. This spectrometer is based on pulsing and bunching of the primary beam and is currently operating with a timing resolution of approximately 390 picoseconds. The second spectrometer is dedicated to measurements in materials where positronium formation is promoted. The timing resolution of this spectrometer is designed to be ~ 0.5 nanosecond with an on-sample spot size of 1–2 mm. For both spectrometers, the energy of the positrons can be varied to allow depth profiling with on-sample intensity exceeding 106 e+/s.}, journal={12TH INTERNATIONAL WORKSHOP ON SLOW POSITRON BEAM TECHNIQUES (SLOPOS12)}, author={Hawari, Ayman I. and Gidley, David W. and Moxom, Jeremy and Hathaway, Alfred G. and Mukherjee, Saurabh}, year={2011} }
 @article{hathaway_skalsey_frieze_vallery_gidley_hawari_xu_2007, title={Implementation of a prototype slow positron beam at the NC State University PULSTAR reactor}, volume={579}, ISSN={["0168-9002"]}, DOI={10.1016/j.nima.2007.03.036}, abstractNote={Abstract A prototype beam system was designed and tested to verify the potential of utilizing the North Carolina State University PULSTAR reactor in generating slow positrons. An annealed tungsten converter/moderator was placed at the end of beam tube ♯6 near the PULSTAR core and surrounded by 0.5-mm-thick cadmium cover. Fission and cadmium capture γ-rays were used to drive pair production reactions in the tungsten. The positrons emitted from tungsten were electrostatically focused and guided using a magnetic solenoid until they reached the exit of the biological shield. An aluminum plate that was placed near the exit served as an annihilation target for the positrons. A coincidence counting system was set up to measure the true coincidence rate of the 511 keV annihilation photons that are produced once the slow positrons strike the aluminum target. The data demonstrated the production and control of slow positrons at a rate greater than 10 7 e + /s.}, number={1}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Hathaway, A. G. and Skalsey, M. and Frieze, W. E. and Vallery, R. S. and Gidley, D. W. and Hawari, A. I. and Xu, J.}, year={2007}, month={Aug}, pages={538–541} }
 @article{moxom_hathaway_bodnaruk_hawari_xu_2007, title={Performance analysis of the intense slow-positron beam at the NC State University PULSTAR reactor}, volume={579}, ISSN={["0168-9002"]}, DOI={10.1016/j.nima.2007.04.117}, abstractNote={An intense positron beam, for application in nanophase characterization, is now under construction at the 1 MW PULSTAR nuclear reactor at North Carolina State University (NCSU). A tungsten converter/moderator is used, allowing positrons to be emitted from the surface with energies of a few electron volts. These slow positrons will be extracted from the moderator and formed into a beam by electrostatic lenses and then injected into a solenoidal magnetic field for transport to one of three experimental stations, via a beam switch. To optimize the performance of the beam and to predict the slow-positron intensity, a series of simulations were performed. A specialized Monte-Carlo routine was integrated into the charged-particle transport calculations to allow accounting for the probabilities of positron re-emission and backscattering from multiple-bank moderator/converter configurations. The results indicate that either a two-bank or a four-bank tungsten moderator/converter system is preferred for the final beam design. The predicted slow-positron beam intensities range from nearly 7×108 to 9×108e+/s for the two-bank and the four-bank systems, respectively.}, number={1}, journal={NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT}, author={Moxom, J. and Hathaway, A. G. and Bodnaruk, E. W. and Hawari, A. I. and Xu, J.}, year={2007}, month={Aug}, pages={534–537} }