Cold moderators decrease the neutron energy spectrum below the thermal spectrum by moderating the neutrons in a suitable moderator material at cryogenic temperatures. At the HBS the cold moderator becomes an intrinsic part of the instrument and will be optimized individually to the instrument requirements. Suitable cold moderator materials are e.g. liquid hydrogen H2, solid methane CH4 or solid mesitylene C9H12. Particularly well suited for a one-dimensional cold moderator is para-hydrogen.
A one-dimensional cold finger moderator has been developed in collaboration with the Technical University Dresden. It consists of a long vacuum tube with a small cryogenic moderator vessel (e.g. cylindrical with 10 cm in length and 2 cm in diameter). This design enables the installation of the cold moderator inside the thermal moderator. The cold neutrons can be emitted freely towards the instrument through the extraction channel with a view onto the entire volume of the cylinder. In the prototype design of the cold finger moderator, all supply lines (e.g. cryogenic supply) and wires (e.g. measurement and control) are located inside the vacuum tube but outside of the cold neutron flight path.
Copyright:
— Forschungszentrum Jülich
Copyright:
— Forschungszentrum Jülich
Publications:
T. Cronert et al., Compact and Easy to Use Mesitylene Cold Neutron Moderator for CANS, Physica B, 551, 337, 2018
S. Eisenhut et al., Cryostat for the Provision of Liquid Hydrogen with a Variable ortho-para Ratio for a Low-dimensional Cold Neutron Moderator, EPJ Web Conf., 231, 04001, 2020