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

本研究的最终目的是在100μK以下的超低温下发现氦3-4液体混合物中氦3准粒子的超流性。与纯氦3液体相比，冷却氦3-4混合物是非常困难的，因为换热器和氦3-4液体混合物之间存在巨大的热阻，称为卡皮扎阻力。在本研究中，我们在以往实验的基础上，试图找到计算混合物冷却模拟的最佳条件，主要有以下几个方面的改进：1.在双重核退磁中制造更有效的核级；2.使用比表面积更大的超细铂粉作为热交换器。用8T+15T磁体代替6T+8T磁体制作了不含塑料的样品电池，使冰箱的效率提高了一个数量级，并成功地制备出了比表面积为33m2/g的超细铂粉。我们可以减少塑料的总释热量，因为塑料的行为与外部的热泄漏类似。我们的冷却模拟表明，我们可以将氦3-4液体混合物冷却到50μK。我们还开发了一种新型的硅单晶传感器来检测粘度。如果超细铂粉含有大量的氢，则可能会因邻位-对位转化而产生大量热量。发现我们的铂粉含有1000ppm以上的氢，在真空中加热到500ppm以上就可以脱氢。

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.