No abstract

Executive SummaryRadiation portal monitors used for interdiction of illicit materials at borders include highly sensitive neutron detection systems. The main reason for having neutron detection capability is to detect fission neutrons from plutonium. Most currently deployed radiation portal monitors (RPMs) use neutron detectors based upon 3 He-filled gas proportional counters, which are the most common large area neutron detector. This type of neutron detector is used in the RPMs installed in international locations made by TSA and others, and in the Ludlum and Science Applications International Corporation RPMs deployed primarily for domestic applications. There is a declining supply of 3 He in the world and, thus, methods to reduce the use of this gas in RPMs with minimal changes to the current system designs and sensitivity to cargo-borne neutrons are being investigated.Four technologies have been identified as being currently commercially available and potential alternative neutron detectors to replace the use of 3 He in RPMs. These technologies are: 1) Boron trifluoride-filled proportional counters, 2) Boron-lined proportional counters, 3) Lithium-loaded glass fibers, and 4) Coated wavelength-shifting plastic fibers.Reported here is a summary of the testing carried out at Pacific Northwest National Laboratory on these technologies to date, as well as measurements on 3 He tubes at various pressures. Details on these measurements are available in the referenced reports. Sponsors of these tests include the Department of Energy (DOE), Department of Homeland Security (DHS), the Department of Defense (DoD), and internal Pacific Northwest National Laboratory funds.The purpose of this testing was to measure the efficiency and gamma sensitivity of the various neutron detection systems and configurations to determine which of these technologies could meet the neutron detection requirements while not exceeding the current footprint of the 3 He-based neutron module in the RPMs. The measurements made as part of this testing included the response of each system to moderated neutrons and to a high gamma-ray exposure rate. As part of this testing, various configurations of 3 Hebased detectors were also measured. The results reported here are from a limited set of tests to measure the capability of each technology listed above to meet the basic requirements. Additional requirements, such as robustness to different environmental conditions, would need to be tested prior to implementation.The requirements used in this testing are from the specification for RPMs developed for the domestic deployments under the Radiation Portal Monitor Project (RPMP). These requirements allow for testing of individual modules with 252 Cf, a common industrial neutron source. Simulations were performed that indicate the TSA system has comparable efficiency per unit surface area, and therefore if the technology meets the RPMP specification, it will likely meet the requirements of the Second Line of Defense (SLD) program for the TSA RPM in the sam...

High-energy photon yields from the reactions ' C + ' ' Sn at 10 MeV/nucleon have been measured. The ratio of cross sections (E~& 30 MeV) o (' Sn)/o (" Sn) is 1.6 6 0.2, which is larger than expected within the equal-participant model. The elementary n-p-p cross section is evaluated within the neutral scalar 0 meson exchange model, and implemented into a BUU code. The results of the BUU calculation suggest that the high-energy p-ray yield differences for the two Sn isotopes arise from the differences in nucleon phase-space distributions. The sensitivity of the high-energy photon production to the initial phase-space conditions is explored.PACS number(s): 25.70.z

In this study, we extended Bateman’s [Proc. Cambridge Philos. Soc. 15, 423 (1910)] original work for solving radioactive decay chains and explicitly derived analytic solutions for generic exit-only radioactive decay problems under given initial conditions. Instead of using the conventional Laplace transform for solving Bateman’s equations, we used a much simpler algebraic approach. Finally, we discuss methods of breaking down certain classes of large decay chains into collections of simpler chains for easy handling.