Device for Writing the Time Tail from Spallation Neutron Pulses
- Paul
- Luc L.
Recent work at Los Alamos Neutron Science Center (LANSCE), has shown that there are large gains in neutron beam intensity to be made by using coupled moderators at spallation neutron sources. Most of these gains result from broadening the pulse-width in time. However the accompanying longer exponential tail at large emission times can be a problem in that it introduces relatively large beam-related backgrounds at high resolutions. We have designed a device that can reshape the moderated neutron beam by cutting the time-tail so that a sharp time resolution can be re-established without a significant loss in intensity. In this work the basic principles behind the tail-cutter and some initial results of Monte Carlo simulations are described. Unwanted neutrons in the long time-tail are diffracted out of the transmitted neutron beam by a nested stack of aperiodic multi-layers, rocking at the same frequency as the source. Nested aperiodic multi-layers have recently been used at X-ray sources and as band-pass filters in quasi-Laue neutron experiments at reactor neutron sources. Optical devices that rock in synchronization with a pulsed neutron beam are relatively new but are already under construction at LANSCE. The tail-cutter described here is a novel concept that uses existing multi-layer technology in a new way for spallation neutrons. Coupled moderators in combination with beam shaping devices offer the means of increasing flux whilst maintaining a sharp time distribution. A prototype device is being constructed for the protein crystallography station at LANSCE. The protein crystallography station incorporates a water moderator that has been judiciously coupled in order to increase the flux over neutron energies that are important to structural biology (3-80meV). This development in moderator design is particularly important because protein crystallography is flux limited and because conventional ambient water and cold hydrogen moderators do not provide relatively large neutron fluxes over this neutron energy range.
- Research Organization:
- Los Alamos National Laboratory.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 975746
- Report Number(s):
- LA-UR-01-5197; TRN: US1006774
- Resource Relation:
- Conference: "Submitted to: Proceedings of SPIE-The International Society for Optical Engineering, Remote Sensing Technology&Applications, July 2001, San Diego."
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
BEAM PULSERS
BEAM SHAPING
CRYSTALLOGRAPHY
LANL
MODERATORS
MONTE CARLO METHOD
NEUTRON BEAMS
NEUTRON SOURCE FACILITIES
NEUTRON SOURCES
NEUTRONS
PROTEIN STRUCTURE
PULSES
SPALLATION
SYNCHRONIZATION
TIME RESOLUTION
WAVELENGTHS
X-RAY SOURCES