DOI 10.1140/epja/i2008-10661-y Special Article – Tools for Experiment and Theory Eur. Phys. J. A 38, 115–123 (2008) T HE EUROPEAN P HYSICAL JOURNAL A Neutron experiments with cryogenic methane hydrate and mesitylene moderators K. N¨ unighoff 1, a , Ch. Pohl 1 , S. Koulikov 3 , F. Cantargi 4 , H. Conrad 1 , D. Filges 1 , H. Gl¨ uckler 1 , F. Goldenbaum 1 , R. Granada 4 , G. Hansen 1 , T. Matzerath 1 , N. Paul 1 , S. Petriw 4 , H. Schaal 1 , H. Soltner 1 , H. Stelzer 1 , W. Ninaus 2 , and M. Wohlmuther 5 1 Forschungszentrum J¨ ulich GmbH, J¨ ulich, Germany 2 Institut f¨ ur Technische Physik, Technische Universit¨at Graz, Austria 3 Joint Institute of Nuclear Research, Dubna, Russia 4 Centro Atomico Bariloche, Bariloche, Argentina 5 Paul Scherrer Institut, Villigen, Switzerland Received: 30 June 2008 / Revised: 16 September 2008 Published online: 21 October 2008 – c  Societ`a Italiana di Fisica / Springer-Verlag 2008 Communicated by J. ¨ Ayst¨o Abstract. In this article we describe the experimental results of a methane hydrate moderator as well as as mesitylene moderator operated at a temperature around 20 K at the JESSICA (J¨ ulich Experimental Spallation Target Set-up In COSY Area) experiment at the J¨ ulich cooler synchrotron COSY. For the first time the cold neutron spectrum of a methane hydrate moderator was experimentally investigated. A comparison with a solid methane and an ice moderator at T = 20 K will be shown. MCNPX simulations with new developed S(α, β) scattering kernels will be compared with experimental data. The applicability of mesitylene and methane hydrate as cold moderators at spallation neutron sources will be discussed. PACS. 24.10.Lx Monte Carlo simulations (including hadron and parton cascades and string breaking models) – 25.40.Fq Inelastic neutron scattering – 28.20.-v Neutron physics – 28.20.Gd Neutron transport: diffusion and moderation 1 Introduction The increasing interest in cold or multi-spectral —i.e. a combination of a cold and a thermal energy spectrum— neutron beams motivated the search for a reliable moder- ator material fulfilling these requirements. Usually liquid hydrogen (e.g. [1–6]) or liquid deuterium (e.g. [7]) is used as moderator material to generate cold neutron beams. Colder energy spectra around 2–3 meV can be achieved by using solid methane [8–11] at temperatures around T = 20 K. One approach for achieving a multi-spectral neutron beam is the superposition of two neutron beams —one from a thermal moderator and one from a cold moderator— with a neutron optic device based on super mirrors [12, 13]. A second way to generate multi-spectral neutron beams is the application of composite modera- tors. This could be a combination of a thermal water and a liquid-hydrogen moderator [1] or a combination of solid methane and liquid hydrogen [14]. In this article we dis- cuss a different solution, the combination of solid methane and ice-methane hydrate. This material contains a single a e-mail: k.nuenighoff@fz-juelich.de methane molecule trapped in a cage-like structure of six frozen water molecules. This combination of materials is believed to result in a peak neutron flux over a broader energy range than any of the single materials [15]. The second topic of this article focuses on the feasibility of mesitylene as a cyrogenic moderator material. It will be demonstrated that a mesitylene moderator delivers a neu- tron spectrum similar to liquid hydrogen at T = 20 K. Furthermore, mesitylene shows no radiation damage [16] and thus it will be well suited for application in high ra- diation fields. 2 The JESSICA experiment The presented results have been obtained with the JES- SICA experiment [17,18] at the J¨ ulich Cooler Synchrotron COSY. JESSICA is a 1 : 1 mock-up of the target, mod- erator, and the reflector assembly as it is described in the technical design study of the European Spallation Source (ESS) [19]. The neutrons were generated by spallation in- duced by a short proton pulse. The parameters of the pro- ton pulse are listed in table 1. As a spallation target a 35 l