Superflow phenomenon has long been discovered, but it was not until 1970s that British scientist anthony leggett discovered that the atomic pair of helium isotope helium -3 was similar to the electronic pair of metal in superconductor. His theory fundamentally explains how helium atoms interact and enter the ordered state of superfluid. Superflow phenomenon is a quantum effect in the macro scope. Due to Bose-Einstein condensation, helium atoms form a "compact group". Superflow is the concrete manifestation of this phenomenon. Boson system is not limited by Pauli principle, and because particles always spontaneously jump to low energy levels, bosons tend to condense to ground energy levels, which is the basic reason for superfluidity.
Since kamerlingh onnes realized the liquefaction of helium, the research on the physical properties of materials at low temperature has gradually deepened, and superconductivity and superfluidity at low temperature have been discovered one after another. In 1930s, it was found that when the temperature of liquid helium (4He) dropped to 2. 17K, liquid helium suddenly changed from the original normal fluid to a series of "superfluids" with unusual properties, which is the superfluid phenomenon.
Superfluid liquid helium has the following characteristics
Below 2. 17K, superfluid liquid helium has the following characteristics:
First, liquid helium can flow along a very thin capillary (about 0. 1 micron in diameter) without showing any viscosity. This phenomenon was first observed by Capicha in 1937, which is called superfluidity.
Secondly, if a thin disk is suspended by filaments and immersed in liquid helium, the disk will be subjected to torsional vibration and its movement will not be resisted.
Thirdly, when the liquid helium flows out of the container A through a porous plug (or a very thin capillary), the temperature of the liquid helium in the container A increases. This phenomenon is as good as mechanical heating. The opposite process is called heat engine effect, that is, when the temperature in A rises, the liquid level of liquid helium will rise. If a is a capillary, liquid helium will be observed to be ejected from the upper mouth, so it is also called fountain effect.
In addition, the thermal conductivity of liquid helium is very good, which is 800 times that of copper at room temperature.
These properties are macroscopic phenomena, but they are actually quantum effects of superfluid liquid helium. Different from macroscopic objects, microscopic particles have an "internal" angular momentum-spin besides the momentum in coordinate space. Roughly speaking, it can be regarded as a small rotating gyro with very small magnetic moment. Particles with semi-integer spins are called fermions, such as electrons, neutrons and protons, and their spins are 1/2. Particles with integer spins are called bosons, such as photons and p mesons, and their spins are 1. For fermions, due to the Pauli exclusion principle, only one particle is allowed to be filled in each state. For bosons, the number of particles in each state is unlimited. After the temperature drops to a certain value, more and more bosons are at the lowest energy, that is, the momentum is zero. This phenomenon is called Bose-Einstein condensation. The condensation mentioned here is not the condensation of gas into liquid, but "momentum condensation". That is to say, many molecules turn to zero momentum, so that they are in the coordinate space, or in the liquid in the container, and the fluidity of the liquid suddenly changes. Liquid helium (4He) is a boson, and the superfluid transition below 2. 17K is this kind of "condensation".
Superflow phenomenon of helium 3
It was not until the late 1970s that scientists observed the superfluid phenomenon of helium 3, because the temperature that caused the superfluid phenomenon of helium 3 was only one thousandth of that of helium 4. Einstein predicted that when the atomic gas is cooled to a very low temperature, all atoms will condense in the lowest energy state, which is called Bose-Einstein condensation. Eber condensed matter is a superconductor and superfluid, which is actually a semi-quantum state. In the semi-quantum state, fermions can condense in large quantities in a narrow space like bosons. The outer core is a condensed Bohai superfluid substance, and the inner core is composed of neutrinos, all of which are in the form of high density and mass.
Superfluid is an ideal fluid with peculiar properties at ultra-low temperature, that is, there is no viscosity inside the fluid. The application of superfluid principle is still under study. However, there has been a dawn in this field. In 2002, German scientists realized the reversible conversion between superfluid state and insulating state of rubidium atomic gas. The scientific and technological circles in the world believe that this achievement will bring a major breakthrough to the research of quantum computers. This achievement was rated as one of the top ten scientific and technological advances in the world in 2002 by academicians of China Academy of Sciences.
The most attractive thing about Helium 3 is its excellent "potential" as an energy material. Deuterium and helium 3 can carry out nuclear fusion without producing neutrons, so the radioactivity is small and the reaction process is easy to control, which can be regarded as neither pollution nor safety. Helium 3 can be used not only for ground nuclear power plants, but also as fuel for rockets and spaceships, especially for space navigation. For every ton of helium 3 extracted from lunar soil, 6300 tons of hydrogen, 70 tons of nitrogen and 1600 tons of carbon can be obtained.
According to experts' calculations, if helium -3 nuclear fusion is used to generate electricity, the total annual power generation in the United States only needs to consume 25 tons of helium-3; 1992 China's total annual power generation is only 8 tons of helium 3, and it is enough for the world to generate electricity with 100 tons of helium 3 a year. Based on the current global electricity price and space transportation cost, the value of 1 ton helium 3 is about $4 billion, and with the development of space technology, the space transportation cost will definitely drop greatly. Recently, French scientists announced that in 2030, nuclear fusion power generation using helium 3 will be commercialized. It is estimated that if there are 5 million tons of helium 3 reserves on the moon, it can support the earth's electricity for more than 10 thousand years!
Supercurrent phenomenon and lunar exploration engineering
Since 1990s, including China, Israel, Japan, India and other countries, mankind has set off a new round of lunar exploration climax. In this lunar exploration climax, the mysterious helium 3 element has become the common goal of the whole world. Helium 3 is an isotope of helium, which contains two protons and one neutron. Helium 3 originally existed in the solar wind, which is a stream of high-energy particles ejected by the sun. On the moon with almost no atmosphere, the solar wind directly falls on the surface of the moon and accumulates over time. In the sand of the moon, the content of helium 3 is increasing, which has become an important part of the lunar soil.
China people's idea of exploring the moon
Chang 'e-1, which cost 65.438+0.4 billion yuan and took three and a half years to build, flew into space on the evening of June 24, 2007 and circled the moon on the morning of June 5, 2007. China people explore the moon has four preliminary ideas:
First, it is very important for us to take a comprehensive three-dimensional photo of the moon and take all the images of the moon. Although the United States has landed on the moon several times, it has not yet had a comprehensive image;
The second is to detect various mineral elements on the moon through spectral analysis. It is estimated that there are more than 100 kinds of mineral elements on the moon, and the United States has detected 5 kinds. We will add 9 kinds this time, and we will detect 14 kinds of elements.
Third, detect the thickness of the soil on the moon. For example, by measuring the thickness of the soil, we can know that there is "helium 3". There are a large number of chemical elements called "Helium 3" in the lunar soil, which is a gas property and a very important fusion energy source.
Fourth, explore the space environment of the earth and the moon during the flight.
Helium 3 resource
It is said that it takes about 173 hours for "Chang 'e I" to reach the moon, and there will be Japanese, Indians and Israelis coming to the moon later. But obtaining helium 3 is undoubtedly a main purpose. It is estimated that there are 6.5438+0 million to 5 million tons on the moon, and there is another saying that there are 6.5438+0 million to 6.5438+0.5 million tons. Of course, I prefer to believe the former. It is said that if "Helium 3" is used to generate electricity in the world, it can last at least 1 10,000 years.
In addition, helium 3 also has great magic in military and medical fields.
The newly discovered superfluid phenomenon
Superflow phenomenon with both boson and fermion properties
In the world of quantum mechanics, we can often see surprising new discoveries. For example, scientists have recently discovered a new superfluid, which has very strange properties and cannot be explained by other superfluids. This discovery was made by Aurel Bulgac and Joaquin E. Drut of seattle university, Washington, USA, in cooperation with Piotr Magierski of Warsaw University of Technology. It provides scientists with a new type of mixed superfluid with both fermion and boson properties. The research paper was published in the journal Physical Review Letters on March 10.
Bulgac said, "By simply changing the temperature, you can turn a boson system into a Fermi subsystem. So far, this phenomenon is not common in any other system. "
Different from ordinary superfluids