[en] The Spallation Neutron Source (SNS), under construction at Oak Ridge National Laboratory, will be the premier facility for neutron scattering studies in the United States. From the outset the SNS can achieve additional flexibility and accommodate a broader range of scientific investigation than would be possible with only the High Power Target Station by utilizing two target stations, each operating under a separate set of conditions and optimized for a certain class of instruments. A second target station, termed the Long-Wavelength Target Station (LWTS), would operate at a lower pulse rate (e.g., 10 vs. 60 Hz) and utilize very cold moderators to emphasize low-energy (long wavelength) neutrons. The LWTS concept discussed here obtains the highest low-energy fluxes possible for neutron scattering instruments by using a heavy-water-cooled solid tungsten target with two moderators in slab geometry and one in a front wing position. The primary focus has been on solid methane moderators, with liquid methane and hydrogen also considered. We used MCNPX to conduct a series of optimization and sensitivity studies to help determine the optimal neutronic parameters of the LWTS. We compared different options based on the thermal and epithermal fluxes as determined by fitting the spectral intensity of the moderators with a Maxwellian peak and a modified Westcott function. The primary parameters are the moderator positions and composition and the target size. We report results for spectral intensity, pulse shapes, high-energy neutron emission, heating profiles in the target, and target activation

[en] Potential diversion of nuclear materials is a major international concern. Fissile (e.g., U, Pu) and other nuclear materials (e.g., D, Be) can be detected using 6-7 MeV gamma rays produced in the ¹⁹F(p,αγ)¹⁶O reaction. These gamma rays will induce neutron emission via the photoneutron and photofission processes in nuclear materials. However, they are not energetic enough to generate significant numbers of neutrons from most common benign materials, thereby reducing the false alarm rate. Neutrons are counted using an array of BF3 counters in a polyethylene moderator. Experiments have shown a strong increase in neutron count rates for depleted uranium, Be, D₂O, and ⁶Li, and little or no increase for other materials (e.g., H₂O, SS, Cu, Al, C, ⁷Li). Gamma source measurements using solid targets of CaF₂ and MgF₂ and a SF₆ gas target show that proton accelerator of 3 MeV and 10-100 microampere average current could lead to acceptable detection sensitivity

[en] We measured the photon yields for proton energies between 1.5 and 4.25 MeV using both CaF₂ and MgF₂ solid targets and SF₆ gas targets. Photon yields were measured using a 7.62 cm x 7.62 cm NaI scintillator detector. Detector response functions for these three individual γ-rays were calculated using the Monte Carlo code MCNP-4C. The relative intensities of the three γ-rays were determined by a least-squares fit of these response functions to the data in a selected region of the pulse-height spectrum. A maximum photon yield of 6.0x10⁷ γ/(micro)C/sr (at 0 degrees) was determined for the sum of these three γ-rays at an effective proton energy of 4.0 MeV. The contribution of the individual lines to the total photon yield depends strongly on the incident proton energy

[en] CINDER is a transmutation code, developed originally at the Bettis Atomic Power Laboratory, which predicts induced radioactivity due to either reactor or accelerator-driven radiation sources. The code and associated data libraries have been expanded and improved over the years at Los Alamos National Laboratory. CINDER08 is the latest update in the series and represents a complete rewrite of CINDER, improving it in many areas. Beginning with CINDER90, several Perl scripts were developed to treat multi-cell problems in combination with the radiation transport code MCNPX. These scripts simplified the preparation of CINDER input and made the code much more user-friendly. In concert with the development of CINDER08, these scripting tools have also been updated. The script developers are intensive users of CINDER and had significant input into the development of CINDER08. CINDER08, through use of these scripts, also works with output from MCNP5, which is useful for problems that do not require the extended particle capabilities of MCNPX and do not require particle energies outside of the tabular physics regime, and with MCNP6. A new version of CINDER, CINDER08, incorporates many improvements to the coding and the data libraries. Updated versions of scripting tools improve the code's usability and simplify the use of CINDER output as the basis of gamma source terms for subsequent calculations. (authors)