The Spallation Neutron Source (SNS) is an accelerator-based short-pulse neutron scattering facility designed to provide an order of magnitude more power than the most powerful existing facility of this type. The SNS is being constructed at Oak Ridge National Laboratory and is on schedule for completion in 2006. The unprecedented power of this facility brings many new opportunities and challenges for neutron scattering instrumentation. This instrumentation will cover a broad spectrum of science, with every instrument designed to be best-in-class. The SNS has provisions to accommodate up to 24 neutron beam instruments, and design and construction of a number of these instruments are already underway. Some of these instruments are funded within the SNS construction project and some from external sources. This paper will discuss the status of these funded instrumentation activities and of some other instrumentation activities in the planning stage, and will also discuss the process for providing additional instruments. The paper will also indicate the performance expected from many of these instruments and will address some of the challenges and opportunities faced in instrumenting a new spallation source of this unprecedented intensity.
The Small Angle Diffractometer (SAD) at the Intense Pulsed Neutron Source (IPNS) utilizes a 20 X 20 cm2 Borkowski-Kopp type 3He position sensitive detector (PSD) which has reliably performed small-angle neutron scattering experiments for more than a decade. The pulsed-source based SAD employs a small, but fixed, sample-to-detector distance and a pulsed polychromatic neutron beam. The neutron energies are resolved through time-of- flight (TOF) measurements so that a much wider range of momentum transfer is probed in a single measurement compared to the range of spectrometers using monochromatic incident beams. However, the pulsed source requires a short sample-to-detector distance so that the detector covers a large solid angle, but with lower angular resolution, and this situation puts stringent demands on the spatial resolution of the detector. Previously, nonlinearities in the position encoding of detected neutrons required that the outer channels of the detector, representing 40% of the detector area, be discarded. This paper presents a technique to characterize both the position encoding and the position resolution of the entire detector so that the whole detector can be used for SANS measurements.
This paper sets forth the fundamental principles governing the development of position- sensitive detection systems for slow neutrons. Since neutrons are only weakly interacting with most materials, it is not generally practical to detect slow neutrons directly. Therefore all practical slow neutron detection mechanisms depend on the use of nuclear reactions to 'convert' the neutron to one or more charged particles, followed by the subsequent detection of the charged particles. The different conversion reactions which can be used are discussed, along with the relative merits of each. This is followed with a discussion of the various methods of charged particle detection, how these lend themselves to position-sensitive encoding, and the means of position encoding which can be applied in each case. Detector performance characteristics which may be of importance to the end user are discussed and related to these various detection and position-encoding mechanisms.
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