Initial performance of sealed straw modules for large area neutron science detectors
Alternative neutron detection technologies must be considered, to overcome limitations imposed by a depleting 3He supply. We have developed a detector technology based on close-packed arrays of boron-coated straws (BCS) in two configurations: (1) each is 4 mm in diameter and 1 m long, and are packaged in groups of 7 that fit inside a single sealed aluminum tube (1.27 cm in diameter, 1 m long); (2) each is 7.5 mm in diameter and 2 m long, and are packaged in groups of 7 that fit inside a single sealed aluminum tube (2.54 cm in diameter, 2 m long). It thus allows operation of the straw detectors in sealed mode, for indefinite periods of time, and in vacuum environments, as required in neutron scattering instruments. The sealed detector modules form a large area (e.g., 1×1 m2, 2×1 m2) neutron imager. Initial testing of the sealed straw detector bundles showed promising results in straw decoding, detector life time, longitudinal resolution, and gas gain stability. The 3D resolution is expected to be 4 mm × 4 mm × 4 mm in configuration #1 and 2.5 cm × 2.5 cm × 2.5 cm in configuration #2, throughout the entire imaging area. Negligible gas gain change was seen over the long test period, in different sealed straw detectors. In addition to facilitating operation in vacuum, another advantageous aspects of the sealed straw detector bundle technique are high portability and structural versatility. Detector modules are easy to transport and detector arrays can be easily installed and tailored to a multitude of different scattering experimental setups. The depth of the detector array can be easily tailored to the desired neutron wavelength and the size and configuration of panels varied of a wide range while utilizing the same elemental modules.
The Evolution of Neutron Straw Detector Applications in Homeland Security
The dwindling supply of 3He has necessitated the adoption of new technologies for detection of neutrons especially in Homeland Security (HS), where detectors require large volumes of the precious gas. The boron-coated straw (BCS) technology consists of very thin-walled metal tubes equipped with a highly robust coating of 10B4C on the inner wall. The coating, applied with Physical Vapor Deposition (PVD), is atomically bound to the metal substrate, and it is able to resist delamination over a temperature range from -200° C to 1000° C. Accelerated lifetime testing of sealed straw detectors over extreme temperature ranges (-70° C to +125° C) have recently demonstrated a 99% expected lifetime of 30 years. At the same time, the coating purity is high, with a 10B content approaching 77%. Straws stacked 5 deep in a dense array have demonstrated an efficiency of > 70% when evaluated in a cold neutron beam. A number of field worthy HS detectors have been developed over the past 2 years based on the BCS. Examples are presented, including neutron modules for Radiation Portal Monitors (RPM), a vehicle mounted modular detector with an intrinsic efficiency of 30% for unmoderated 252Cf neutrons, and handheld detectors. All of these systems have been government tested. The 10B4C coated straw offers a highly versatile, robust and low cost technology meeting multiple needs in homeland and international security.
Creating the Virtual Universe
Simulation software is important to our understanding of the universe. The intrinsic multiphysics aspects are spiced with a range of temporal scales and spatial scales, both of which cover more digits than are available in the standard hardware. This, together with the intrinsic chaotic nature of many physical processes, poses quite a challenge. To meet this challenge, researchers developed the Astronomical Multipurpose Environment (AMUSE). Instead of writing a suite of multiphysics solvers from scratch, AMUSE's developers coupled existing solvers for each physical ingredient. The result is a highly inhomogeneous collection of dedicated solvers with a homogeneous protocol that scales to supercomputers.