A Combined Cryostat for Neutron and Optical Investigations

A two-chamber metal cryostat with a volume of six liters of liquid helium for neutron and optical studies of impurity gel samples in liquid helium was designed. The cryostat allows long-term, up to 20 h, measurements at helium temperatures without adding liquid helium to it. The sample preparation site in the cryostat is spaced (the working cell is raised up) with the location of the working cell during the research (the cell is shifted down to the cryostat tail). The samples are prepared by condensing gaseous 4Не with a small admixture of vapors of an investigated substance on the surface of superfluid He-II in a quartz-glass cell at a temperature of 1.8 K. Transparent quartz-glass windows in the upper part of the cryostat make it possible to observe the process of preparing an impurity gel sample in the working cell. The quartz windows in the bottom part (tail) of the cryostat are intended for adjusting the position of the working cell and carrying out optical research. Subsequently, in a modernized cryostat design for neutron studies, the tail shell with the optical windows was replaced by a continuous thin-walled cup that was turned from an aluminum billet. The results of studying the transmission and small-angle scattering of cold neutrons in water-gel samples in superfluid and normal 4Не are presented for illustration.