Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 7: Matter at Low Temperature: Poster Session
TT 7.11: Poster
Montag, 25. Februar 2008, 14:00–18:00, Poster B
Dynamics of liquid 3He-4He-mixtures studied with Neutron Radiography — •Mark Faist1, Hartmut Abele2, Roland Gähler3, and Andreas Van Overberghe3 — 1Physikalisches Institut, Universität Heidelberg — 2E18, Technische Universität München — 3Institut Laue-Langevin, Grenoble
Using a Neutron Radiography setup, we visualize the dynamics in superfluid 3He-4He-mixtures and the process of phase separation. These measurements give a deeper insight into critical phenomena and universal scaling laws and with our method we have also direct access to transport processes in He-II driven by temperature gradients.
We perform a measurement of the mass diffusion coefficient of 3He in superfluid 4He for a wide temperature range of 0.5-1.3K, where only poor data exists. Using a scintillator and CCD-Camera as detector, we map the 3He concentration with a spatial resolution of 0.5 mm by measuring the neutron absorption. The concentration distribution varies as a function of applied heating power and distance from the heater, so the mass diffusion coefficient can be determined directly. There is also some need for understanding these processes in a search for a permanent electric dipole moment of the neutron.
Even time-resolved measurements up to 20 fps are possible and has been be used for the observation of phase separation in 3He-4He mixtures with higher 3He concentration. The transitions from the superfluid and the normalfluid mixtures into the phase separation zone could be observed, where inconsistent experiments and theories exist.
This work was funded by the German Federal Ministry for Research and Education under Contract No. 06HD187.