Melinda Sweany

Source detection at 100 meter standoff with a time-encoded imaging system

Abstract We present the design, characterization, and testing of a laboratory prototype radiological search and localization system. The system, based on time-encoded imaging, uses the attenuation signature of neutrons in time, induced by the geometrical layout and motion of the system. We have demonstrated the ability to detect a ∼ 1 mCi 252 Cf radiological source at 100 m standoff with 90% detection efficiency and 10% false positives against background in 12 min . This same detection efficiency is met at 15 s for a 40 m standoff, and 1 . 2 s for a 20 m standoff.

Low light event reconstruction simulations for an optically segmented single volume scatter camera

Dual plane neutron scatter cameras have shown promise for localizing fast neutron sources. The condition that a neutron must scatter in both planes of the camera produces low counting efficiencies. Counting efficiency can be improved using an alternative design that uses a single, optically segmented volume of scintillation material. Using Geant4, we simulated pulses from neutron elastic scatter events at different locations throughout an EJ-204 scintillator bar. We used nonlinear regression on low light pulses to determine the position along the bar where the scatter event occurred.

Remote Reactor Monitoring Annual Report

The overall goal of the WATCHMAN project is to experimentally demonstrate the potential of water Cerenkov antineutrino detectors as a tool for remote monitoring of nuclear reactors. In particular, the project seeks to field a large prototype gadolinium-doped, water-based antineutrino detector to demonstrate sensitivity to a power reactor at ~10 kilometer standoff using a kiloton scale detector. The technology under development, when fully realized at large scale, could provide remote near-real-time information about reactor existence and operational status for small operating nuclear reactors.

Bubble masks for time-encoded imaging of fast neutrons

Time-encoded imaging is an approach to directional radiation detection that is being developed at SNL with a focus on fast neutron directional detection. In this technique, a time modulation of a detected neutron signal is induced-typically, a moving mask that attenuates neutrons with a time structure that depends on the source position. An important challenge in time-encoded imaging is to develop high-resolution two-dimensional imaging capabilities; building a mechanically moving high-resolution mask presents challenges both theoretical and technical. We have investigated an alternative to mechanical masks that replaces the solid mask with a liquid such as mineral oil. Instead of fixed blocks of solid material that move in predefined patterns, the oil is contained in tubing structures, and carefully introduced air gaps-bubbles-propagate through the tubing, generating moving patterns of oil mask elements and air apertures. Compared to current moving-mask techniques, the bubble mask is simple, since mechanical motion is replaced by gravity-driven bubble propagation; it is flexible, since arbitrary bubble patterns can be generated by a software-controlled valve actuator; and it is potentially high performance, since the tubing and bubble size can be tuned for high-resolution imaging requirements. We have built and tested various single-tube mask elements, and will present results on bubble introduction and propagation for different tube sizes and cross-sectional shapes; real-time bubble position tracking; neutron source imaging tests; and reconstruction techniques demonstrated on simple test data as well as a simulated full detector system.