A dilution refrigerator is a cryogenic

Cryogenics

In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...

 device first proposed by Heinz London

Heinz London

Heinz London was a German Physicist. He worked with his brother Fritz on superconductivity, discovering the London equations when working in Oxford, at the Clarendon Laboratory; these equations gave a first explanation to the Meissner effect...

. Its refrigeration process uses a mixture of two isotope

Isotope

Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

s of helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

: helium-3

Helium-3

Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...

 and helium-4

Helium-4

Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

. When cooled below approximately 870

Orders of magnitude (temperature)

-Detailed list for 100 K to 1000 K:Most ordinary human activity takes place at temperatures of this order of magnitude. Circumstances where water naturally occurs in liquid form are shown in light grey.-External links:*...

 millikelvin

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

, the mixture undergoes spontaneous phase separation to form a ³He-rich phase and a ³He-poor phase.

As with evaporative cooling, energy is required to transport ³He atoms from the ³He-rich phase into the ³He-poor phase.