Page 82 - ILLS Annual Report 2018

TECHNICAL AND COMPUTING DEVELOPMENTS
Development of a low-roughness, transparent, hydrogen-tight sample container for ultracold and very cold neutron experiments
The loss mechanisms in ultracold neutron converters based on solid deuterium are still poorly understood.
To gain more knowledge about them, neutron transmission measurements need to be carried out on deuterium. We have developed a sample container with low-roughness, amorphous silica windows that allows for the precise measurement of the total cross section
of cryogenic liquids and solids, while suppressing surface scattering.
AUTHORS
S. Dögé and J. Hingerl (ILL and TU Munich, Germany) C. Morkel (TU Munich, Germany)
T. Jenke (ILL)
ARTICLE FROM
Sci. Instrum. (2018)—doi: 10.1063/1.4996296
REFERENCES
[1] F. Atchison et al., Nucl. Instrum. Methods A 611 (2009) 252 [2] G. Bison, D. Ries et al., Phys. Rev. C 95 (2017) 045503
[3] S. Dögé and J. Hingerl, Rev. Sci. Instrum. 89 (2018) 033903 [4] S. Dögé et al., Phys. Rev. B 91 (2015) 214309
For several decades, the ultracold neutron facility PF2 has been providing the highest density of ultracold neutrons (UCNs) worldwide. Nevertheless, most experiments performed at PF2 have been limited by neutron counting statistics, triggering the development of new UCN converters based on solid deuterium (sD2) across Europe and North America. Initial simulations and test measurements predicted a significant increase in UCN density compared with that achieved by PF2 [1]. This density is the crucial parameter
in any UCN storage experiment. However, the actual UCN output of these new converters is lower than expected [2].
This discrepancy might be explained by the scattering of UCNs from rough surfaces and defects inside the sD2 crystal.
We have conceived, constructed and tested a sample container for cryogenic liquids and solids that addresses the issue of surface scattering [3] (see figure 1). Its highly polished, amorphous silica windows, which are its key feature, allow samples to be grown with a smooth
Figure 1
Sample container with highly polished and transparent windows.
ANNUAL REPORT 2018