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Monte Carlo radiation transport codes have become the primary tool for shielding and activation analysis at high-powered spallation neutron sources. However, use of these codes to model facilities that have large amounts of shielding requires the use of variance reduction methods. This paper presents examples that apply ADVANTG generated variance reduction parameters to analyses performed at ESS using MCNP6. This requires some limitations in ADVANTG to be overcome and little-known features to be used. The focus of this paper is to describe how these limitations were overcome so other analyst at spallation sources can benefit from these methods as well. [ABSTRACT FROM AUTHOR]

Rotating objects, such as choppers, are common components of a neutron beamline, and the motion of these components is not described in the static geometry of an MCNPX model. The special case of non-static surfaces for rotation about a stationary point in space has been developed for MCNPX. In addition, velocity dependent kinematics due to the motion of the medium have been implemented. This implementation allows for the simulation of rotating objects at speeds comparable to the velocity of cold neutrons. Applications of the chopper extension will be discussed, including the direct simulation of a bandwidth chopper system, the thermalization of neutrons inside a spinning material, and the discussion of the implementation of a spinning single crystal. [ABSTRACT FROM AUTHOR]

VENUS is an imaging instrument that will use a broad range of neutron wavelengths, from epithermal to cold, will include enhanced contrast mechanisms, and will offer novel energy-selective imaging techniques that directly connect the structures, properties, and function of complex engineering materials and systems to reveal practical and fundamental answers about their real-world performance. The instrument is to be built at SNS beam line 10 and will face the decoupled poisoned hydrogen moderator. The driving cost for the instrument is the beam line and instrument cave shielding. Initial scoping analyses were performed to estimate thickness and composition of shielding materials for the instrument cave and beam line. In light of the upcoming Proton Power Upgrade (PPU) project, these transport analyses were performed for proton beam on target at 1.3 GeV and 2 MW. [ABSTRACT FROM AUTHOR]

Fast neutron measurements have been performed with silicon and diamond detectors at nTOF, ChipIr, and CHARM facilities. The detectors have been used in pulse mode; the deposited energy and time stamp is measured event by event for each signal above threshold. The pulsed nature of the spallation sources gives high instantaneous counting rates that dictate the use of a fast electronic chain including a current preamplifier and digital acquisition. The energy-dependent response functions of these detectors to fast neutrons can be extracted from nTOF data using time-of-flight to provide energy tagging. These measured response functions can then be used both to benchmark Monte Carlo simulations of the response functions and to interpret the measurements at ChipIR and CHARM, facilities used for the irradiation of microelectronics, where time-of-flight energy measurement at these neutron energies is not possible. [ABSTRACT FROM AUTHOR]

This contribution describes the computational methodology behind an optimization procedure for a scattered beam collimator. The workflow includes producing a file that can be manufactured via additive methods. A conical collimator, optimized for neutron diffraction experiments in a high pressure clamp cell, is presented as an example. In such a case the scattering from the sample is much smaller than that of the pressure cell. Monte Carlo Ray tracing in MCViNE was used to model scattering from a Si powder sample and the cell. A collimator was inserted into the simulation and the number and size of channels were optimized to maximize the rejection of the parasitic signal coming from the complex sample environment. Constraints, provided by the additive manufacturing process as well as a specific neutron diffractometer, were also included in the optimization. The source code and the tutorials are available in c3dp (Islam (2019)). [ABSTRACT FROM AUTHOR]

An experimental procedure is assessed to obtain moderated neutron fields starting from almost monochromatic 14 MeV neutrons generated by means of an accelerator-driven D-T source. The use of a metallic pre-moderator and a standard hydrogen-containing moderator is effective in producing neutron spectra featuring a thermal peak and an epithermal slowing down tail extending up to 14 MeV. The performance of proposed moderation system was investigated by means of MCNP Monte Carlo calculations, benchmarked against experimental measurements using an explorative set up, assembled at the Frascati Neutron Generator. The benchmarked calculations allow at making predictions about the brilliance of a 14 MeV neutron moderator in view of possible applications in neutron science. [ABSTRACT FROM AUTHOR]

Rotating objects, such as choppers, are common components of a neutron beamline, and the motion of these components is not described in the static geometry of an MCNPX model. The special case of non-static surfaces for rotation about a stationary point in space has been developed for MCNPX. In addition, velocity dependent kinematics due to the motion of the medium have been implemented. This implementation allows for the simulation of rotating objects at speeds comparable to the velocity of cold neutrons. Applications of the chopper extension will be discussed, including the direct simulation of a bandwidth chopper system, the thermalization of neutrons inside a spinning material, and the discussion of the implementation of a spinning single crystal. [ABSTRACT FROM AUTHOR]