Search for Superfluidity in Helium3-4 Mixture by a double Nuclear Demagnetization Method with fine Platinum Powder

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The final goal of this research is to discover a superfluidity of helium 3 quasiparticles in helium 3-4 liquid mixtures at ultra-low temperatures below 100 μK.It is very difficult to cool helium 3-4 mixtures compared with pure helium 3 liquid, because there exists large thermal resistance, called Kapitza resistance, between heat exchangers and helium 3-4 liquid mixtures. In this research, we tried to find the optimum condition witlt computing cooling simulation of the mixtures based on our former experiments improving below items : 1. To make more efficient nuclear stages in a double nuclear demagnetization., 2. To use ultra-fine platinum powder as a heat exchanger, which has larger surface area.3. To make a sample cells without plastics like Stycast.It was found that the efficiency of the refrigerator was leveled up by one order higher using 8T+15T magnets instead of 6T+8T.We also managed to make ultra-fine platinum powder with a huge surface area of 33 m2/g.. We could decrease the total amount of heat release from plastics which has a similar behavior to heat leak from outside. Our simulation of cooling shows that we can cool helium 3-4 liquid mixtures down to 50 μK.we also developed the new type of a sensor made of silicon single crystal to detect the viscosity. If ultra-fine platinum powder contains a large amount of hydrogen, large heat generation due to the ortho-para conversion might be expected. It is found that our platinum powder contains more than 1000 ppm of hydrogen, and the hydrogen can be removed by heating up above 500 ℃ in vacuum.