[en] The divergence and alignment indicator (DAI) was developed to test the alignment of the imaging plane in a neutron beam and to determine the divergence angle of the beam. The construction of the device was intentionally kept simple to allow ease of implementation. The DAI consists of an aluminum plate and rods, and cadmium wire for contrast. The device was tested in the Pennsylvania State University Breazeale Nuclear Reactor neutron radiography beam. Three basic cases (aligned, aligned in only one direction, and completely misaligned), were used to determine that the derived equations for calculating the beam divergence were correct for each case. During the use of a newly fabricated DAI device, it was discovered that the most prominent weakness of the DAI is the precision necessary in the construction. For example, the top of the plate must be precisely flat. Otherwise, the minor differences in height will lead to large discrepancies in the data

[en] A single-disk, 'slow' chopper system has been developed at the Penn State Univ. Radiation Science and Engineering Center (RSEC) for the purpose of energy spectrum measurements on thermal neutron beams (E < 1 eV). The primary beam at PSU RSEC was gated with a single-disk neutron chopper, and the distribution in neutron time-of-flight (TOF) across a known distance was recorded. A procedure was defined whereby the recorded TOF distribution was corrected for various experimental conditions and transformed to yield the velocity and energy spectrum of neutrons in the beam. These data were compared to distributions derived from models based on the Maxwell-Boltzmann distribution. This comparison facilitated characterization of the beam and evaluation of the instrument's usefulness and accuracy in spectroscopic measurements. (authors)

[en] We present a simple methodology for reducing the extent of the search space of the modular optimization code package developed for the size and shape optimization of the beam tube assembly at the Penn State Breazeale Reactor (PSBR). In this method, we express the origin of the neutron output at the beam tube exit in two components depending on the location of their last scattering collision in (i) the Bi gamma shield; or (ii) the moderator (e.g. H₂O or D₂O) illuminating the beam tube. We compute the contribution of these two components to the neutron flux at the beam tube exit by performing numerical experiments using the three-dimensional particle transport code TORT on a model configuration. We illustrate the results of this approach with various moderator materials, comparing the strength and spectrum of the outgoing neutron beam, and indicating how those affect the search space size. Results demonstrate that the neutrons originating at the beam tube base contribute more output neutrons at the beam tube exit than neutrons from all other origination locations. Hence, this result enables defining a small search space, thus reducing the optimization procedure's computational time. (authors)

[en] The Radiation Science and Engineering Center facilities at the Pennsylvania State Univ. (PSU) include the Penn State Breazeale Reactor, gamma irradiation facilities, and various radiation detection and measurement laboratories. Due to inherited design issues with the current arrangement of beam ports and reactor core-moderator assembly, the development of innovative experimental facilities utilizing neutron beams is extremely limited. Therefore, a new core-moderator location in PSBR pool and beam port geometry was needed to be developed. A study is underway with the support of DOE-INIE funds to examine the existing beam ports for neutron output and to investigate new moderator arid beam-port designs to produce more useful neutron beams. The overall system for this study consists of two major parts, the core model and beam port model. Core calculations are performed by using a three dimensional nodal diffusion code ADMARC-H. Beam port calculations are performed with the MCNP code. An interface program has been developed at PSU to link the diffusion code to the neutron transport code. The MCNP model consists of the D₂O tank, graphite reflector block, and beam port tube with their surroundings. The results of the PSU package show good agreement with the experimental data. (authors)