Dilution refrigerators for particle physics experiments: Two variants with sample cooling by helium-4

Two variants are described of 3He-4He dilution refrigerators for experiments with polarized nuclei in particle beams, which often have to be performed under adverse experimental conditions. The first is used for experiments in a beam of cold neutrons that do not allow any 3He on their beam path. The sample is therefore indirectly cooled by liquid 4He. The second variant is used for experiments in a beam of heavy nuclei that only allow a very thin film of material, in this case 4He, to cool a thin polarized polystyrene target. Such a polarized target is a powerful spectroscopic tool to investigate nuclear structure and reaction mechanisms, which is of interest for the study of nuclei far from stability.