Liquid helium

Helium is a gas. It can turn into a liquid. This only happens when it is very cold.

It is much lighter than water. One part of it is like one-eighth of water.

There are two kinds of helium. One is common. The other is rare. Both can become a special liquid. This liquid can flow in a strange way.

This liquid helps big machines stay cool. It works in tools that take pictures of the body. It also works in huge science machines. It is a very useful liquid.

Helium is a gas that we use every day. It can turn into a liquid. This only happens at very cold temperatures.

The first person to make liquid helium was Heike Kamerlingh Onnes. He did this in 1908 in the Netherlands.

There are two types of helium. One is common and is called helium-4. The other is rare and is called helium-3. Both can become a superfluid. A superfluid is a liquid that flows in a strange way.

Liquid helium is very light. It has only one-eighth the density of water. This means it is much lighter than water. It is also used as a refrigerant. A refrigerant is a liquid that helps keep things cold.

Scientists use liquid helium to cool big machines. It cools the magnets in MRI machines. These machines take pictures of the body. It also cools the Large Hadron Collider. That big machine uses 120 tonnes of liquid helium.

Liquid helium is a very special state of matter. It only happens when helium gets extremely cold. At standard pressure, it stays liquid at temperatures near absolute zero. This substance is important because it can become a superfluid. A superfluid is a liquid that flows in a very strange way.

This state of matter helps scientists study how the world works. It is one of the coldest things we can make.

How does helium become a liquid? It all depends on the tiny parts called atoms. Helium atoms do not pull on each other very strongly. This is because helium is a noble gas. Because these attractions are so weak, the gas stays liquid even at very low temperatures.

If you mix the two types of helium, they can separate. The helium-4 type is denser and sinks to the bottom. The helium-3 type is lighter and floats on top. This separation happens to help the liquid reach a lower energy state.

People have been studying this for a long time. A Dutch physicist named Heike Kamerlingh Onnes first liquefied helium. He did this on July 10, 1908, in the Netherlands. He worked at the University of Leiden. Later, a Canadian physicist named John Cunningham McLennan learned how to make it on demand.

Other scientists like Lev Landau and Richard Feynman also did great work. They helped us understand the strange ways liquid helium behaves.

There are two main types of helium to know. The first is helium-4, which is the most common kind. The second is helium-3, which is much rarer. Helium-4 is about one-eighth the density of liquid water.

This means it is very light and thin. Scientists use these different types to reach even colder temperatures. For example, a dilution refrigerator can reach just a few millikelvins. This is much colder than almost anything else.

We use liquid helium in many big machines today. It acts as a cryogenic refrigerant to keep things very cold. This is helpful for superconducting magnets. You might see these magnets used in an MRI machine at a hospital.

It is also used in the Large Hadron Collider. That huge machine uses 120 tonnes of liquid helium to stay cold. Without this liquid, these amazing tools could not work.

Liquid helium is a unique physical state of the chemical element helium. It occurs only at extremely low temperatures when measured at standard atmospheric pressures. This substance is vital to modern science because it can exhibit superfluidity. A superfluid is a liquid that flows in a very unusual way.

Because helium atoms have very weak attractions to one another, the element remains liquid all the way down to absolute zero at standard pressure. This makes liquid helium one of the coldest substances used in scientific research today.

The behavior of liquid helium is driven by the tiny particles called atoms. Helium is a noble gas, which means its atoms do not pull on each other very strongly. These interatomic forces are even weaker due to the effects of quantum mechanics. This is significant because helium has a very low atomic mass of about four daltons. At these low temperatures, the atoms try to find a state with less ground state energy. They do this by naturally increasing the average distance between the atoms. Because these forces are so weak, the helium stays liquid rather than freezing into a solid. To make helium a solid, scientists must apply very high pressures and very low temperatures.

There are two stable isotopes of helium that scientists study: helium-4 and helium-3. Helium-4 is the common isotope found in nature. Helium-3 is a much rarer isotope. These two types of helium behave differently when they are mixed together. Below 0.9 kelvin at their saturated vapor pressure, a mixture of these isotopes undergoes phase separation. This means they split into two distinct layers. The denser superfluid layer, which is mostly helium-4, sinks to the bottom. A normal fluid layer, which is mostly helium-3, floats on top.

This separation happens because the overall mass can reduce its thermodynamic enthalpy by splitting.

Each isotope also has its own unique way of becoming a superfluid. In helium-3, the atoms are fermions. At very low temperatures, these atoms form pairs called Cooper pairs. These pairs act as bosons, which allows them to condense into a superfluid. These Cooper pairs are actually much larger than the distance between the atoms themselves. Helium-4 also undergoes a transition to a superfluid state when it reaches its specific transition temperature. These different behaviors allow scientists to manipulate the liquid for various high-tech experiments.

Humans first achieved the liquefaction of helium on July 10, 1908. A Dutch physicist named Heike Kamerlingh Onnes succeeded in this at the University of Leiden in the Netherlands. At that time, the isotope helium-3 was still unknown because the mass spectrometer had not been invented yet. In 1923, Kamerlingh Onnes advised Canadian physicist John Cunningham McLennan on how to produce liquid helium almost on demand. Later, Soviet physicist Lev Landau and American physicist Richard Feynman performed important work on the characteristics of the liquid. In 1961, researchers Vignos and Fairbank discovered a specific phase of solid helium-4 called the gamma-phase. This phase only exists within a narrow pressure range between 1.45 and 1.78 K.

Liquid helium is used today as a cryogenic refrigerant, which is a substance used to create extreme cold. It is essential for operating superconducting magnets. These magnets are used in many medical and scientific tools. For example, they are used in magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR). They are also used in magnetoencephalography (MEG) and low temperature Mössbauer spectroscopy. The scale of its use can be massive. The Large Hadron Collider uses 120 tonnes of liquid helium to cool its superconducting magnets.

Because of its unique properties, liquid helium is a bridge to understanding advanced physics. Scientists use a device called a dilution refrigerator to reach incredibly low temperatures. This device works by using the way helium-3 and helium-4 interact. At extremely low temperatures, the helium-4 rich superfluid phase can hold up to 6% helium-3 in solution. This allows researchers to reach temperatures of just a few millikelvins. By studying these tiny, cold states, scientists can explore the fundamental rules of the universe and how matter behaves at the very edge of coldness.