[Prex] neutron shielding collimators

[Jay Benesch]

https://arxiv.org/abs/1804.02889

Study of neutron shielding collimators for curved beamlines at the 
European Spallation Source
V. Santoro, D. D. DiJulio, S. Ansell, N. Cherkashyna, G. Muhrer, P. M. 
Bentley
(Submitted on 9 Apr 2018)

     The European Spallation Source is being constructed in Lund, Sweden 
and is planned to be the world's brightest pulsed spallation neutron 
source for cold and thermal neutron beams (≤ 1 eV). The facility uses a 
2 GeV proton beam to produce neutrons from a tungsten target. The 
neutrons are then moderated in a moderator assembly consisting of both 
liquid hydrogen and water compartments. Surrounding the moderator are 22 
beamports, which view the moderator's outside surfaces. The beamports 
are connected to long neutron guides that transport the moderated 
neutrons to the sample position via reflections. As well as the desired 
moderated neutrons, fast neutrons coming directly from the target can 
find their way down the beamlines. These can create unwanted sources of 
background for the instruments. To mitigate such a kind of background, 
several instruments will use curved guides to lose direct line-of-sight 
(LoS) to the moderator and the target. In addition instruments can also 
use shielding collimators to reduce the amount of fast neutrons further 
traveling down the guide due to albedo reflections or streaming. Several 
different materials have been proposed for this purpose. We present the 
results of a study of different options for collimators and identify the 
optimal choices that balance cost, background and activation levels.

Comments: 	10 pages, 10 figures, Proceeding of the 4th International 
Workshop on Accelerator Radiation Induced Activation - ARIA'17, May 
22-24, 2017 Lund, Sweden