Solid deuterium surface degradation at ultracold neutron sources
| Autor: | D. Ries, M. Daum, Christopher Morris, Takeyasu M. Ito, Georg Bison, K. K. H. Leung, C. Cude-Woods, Geza Zsigmond, Bernhard Lauss, B. Wehring, Michael Wohlmuther, S. M. Clayton, Philipp Schmidt-Wellenburg, P. R. Huffman, Mark Makela, Robert W. Pattie, Alexander Saunders, E. Korobkina, Vadim Talanov, T. Bailey, Leah Broussard, A. Anghel, E. M. Lutz, Nora Hild, Klaus Kirch, Ayman I. Hawari, G. Medlin, C. R. White, B. Blau, Albert Young |
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| Rok vydání: | 2018 |
| Předmět: |
Physics
Elastic scattering Nuclear and High Energy Physics Yield (engineering) Physics - Instrumentation and Detectors 010308 nuclear & particles physics Mean free path Hadron FOS: Physical sciences Instrumentation and Detectors (physics.ins-det) 01 natural sciences High Energy Physics - Experiment High Energy Physics - Experiment (hep-ex) Deuterium 0103 physical sciences Ultracold neutrons Neutron source Nuclear fusion Atomic physics Nuclear Experiment (nucl-ex) 010306 general physics Nuclear Experiment |
| DOI: | 10.48550/arxiv.1804.08616 |
| Popis: | Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment (`conditioning') of the sD_2. We show that, in addition to the quality of the bulk sD_2, the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D_2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD_2 frost formation on initially transparent sD_2 in offline studies with pulsed heat input at the North Carolina State University UCN source results in a consistent description of the UCN yield decrease. Comment: 15 pages, 22 figures, accepted by EPJ-A |
| Databáze: | OpenAIRE |
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