Before the advent of cryogenics, the most ‘cooling’ humans used had been in the form of evaporative methods. Cryogenics is the science of attaining extremely low temperatures and studying the nature of matter at those temperatures. The coldest temperature present naturally on Earth is ~ −98 °C (~ −144 °F; ~175.3 K) near East Antarctic Ice (observed using Satellite Thermal Infrared Mapping). The cryogenic temperatures in laboratories range from −150 °C or −238 °F to −273 °C or −460 °F (i.e. absolute zero 0 K).
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Temperature is a measure of heat which arises from the random motion of atoms. As the temperature of any system goes down, the random motion of atoms reduces. They get into an ordered state. When atoms are in motion, the matter is perceived as hot and when they slow down, we perceive that matter as cold. At cryogenic temperatures, the atoms behave as if they were stationary, the atoms are ‘ideally’ still at absolute zero.
“We can make atoms practically stand still”, said Professor Bengt Nagel, in the award ceremony speech for the 1997 Nobel Prize in Physics awarded to William Phillips, Steven Chu, and Claude Cohen-Tannoudji, "for development of methods to cool and trap atoms with laser light."
Low temperatures were achieved by methods such as heat conduction, evaporative cooling, and the Joule-Thompson effect. Lavoisier had predicted that ‘[t]he air, or at least some of its constituents, would cease to remain an invisible gas and would turn into the liquid stage. A transformation of this kind would thus produce new liquids of which we as yet have no idea.’ In 1877, oxygen was first cooled to its liquid state by Louis Cailletet in France and Raoul Pictet in Switzerland.
Thereafter, liquefying different gases became the most important aspect of ‘cryotechnology’. Oxygen is needed in industries such as steel production, and Helium in space technology. Cryotechnology was also driven by the industrial and domestic refrigeration needs; storage and transportation of food across the world revolutionized the food industry. This further fueled the growth of cryogenics research.
By 1980s laboratories produced the impossible temperatures of 0.000001 K, but Ideal 0 K has not yet been practically achieved.
Cryogenics has developed into new fields such as cryoelectronics (also known as cold electronics) cryobiology and cryophysics. Cryogenics has allowed scientists an insight into the engineering of atomic and subatomic matter.
At cryogenic temperatures, the properties of the materials change drastically. Superfluidity, the frictionless flow, was first observed in liquid Helium at temperatures near 0 K. It is analogous to ‘super’ conduction behavior. Kamerlingh Onnes discovered ‘superconductivity’- zero electrical resistance at very low temperatures. Superconductivity leads to an eternally persistent ring current. Superconductors remain non-resistive even in the presence of very high magnetic fields, thus enabling power transmission in heavy-current systems. Superconducting electric motors approaching zero electric losses are also constructed. Electronics that use superconductors are known as cryotronics. Superconductors are also used in particle accelerators. SQUID, the Superconductive QUantum Interference Device, consists of a closed superconductive circuit. It can detect very sensitive magnetic field variations. One of the most useful applications in the medical field is in magneto-cardiography.
Nuclear Magnetic Resonance (NMR) Spectroscopy is possible because of strong magnetic fields generated by supercooling electromagnets. NMR is a very important tool in understanding the chemical properties of atoms and molecules. A complex application of NMR, in MRI (Magnetic Resonance Imaging), is mostly used in health applications. MRI scans provide clear and detailed images of the inside of the human body, helping the medical professionals in diagnosis and prognosis of illnesses.
A ‘dream-mile’ of atomic physicists could be achieved using cryogenics - the Bose-Einstein condensate (BEC) - a new and weird state of matter, was formed when cooled to near absolute zero. A BEC is a group of identical particles that behave as if it were one particle. Albert Einstein first predicted it in 1924 on the basis of quantum theoretical made by the Indian physicist Satyendra Nath Bose. Practically creating BEC in laboratories was only possible because of the understanding and advances made in cryogenics. In 1995, the first BEC was made in a gas of rubidium atoms cooled to 170 nanokelvins (nK). The experimentalists were awarded the 2001 Nobel Prize for Physics that has led to a deeper understanding of quantum physics. BECs being superconducting and superfluid gives physicists a powerful new matter for investigating these phenomena.
The extremely cold atoms also construct precise atomic clocks. The ‘atomic’ oscillations are measured to keep track of time. It is possible to measure the atomic oscillations at extremely low temperatures without any disturbances/noises. The best atomic clock demonstrates a relative precision of 2.5×10−19 — equivalent to ‘an imprecision of 100 ms over the estimated lifetime of the Universe’. In a recent study, the atomic clock is based on an extremely narrow optical transition of Strontium (Sr); thousands of ultracold Sr atoms confined in a 3D optical lattice. These optical lattice atomic clocks are also used to detect gravitational waves in space. The atomic clocks also help operate satellite navigation systems (global positioning system).
At cryogenic temperatures, atoms near stationary stance has made them incredibly sensitive to the environment around them which makes them highly sensitive detectors. Cryodetectors are also used to help detect oil or mineral reserves, and pollution levels. Cryogenic particle detectors are now ready to be used in many high sensitivity experiments in particle physics and in other instrumental applications. Some characteristics of these devices give us the best-performing instruments in measurements of double beta decay, high-resolution X-ray, single optical photon energy, molecular fragment determination, and BEFS (the Beta Environmental Fine Structure). They are also used in search of dark matter. Space missions without cryogenics would not have been possible. An early use of cryogenics was limited to handling liquid hydrogen and liquid oxygen for use as rocket fuels. Liquid oxygen is also used to provide breathable air for astronauts. Aerospace-cryogenic engines, cryogenic propulsion systems, space cryocoolers, cryogenic storage tanks, cryogenic vacuum chambers, and Cryogenic Fluid Management (CFM) technology are just a few cryogenic systems to name that are used in Space technology and research. CFM is important in different fields such as infrared and x-ray astronomy, biological sciences, and fundamental investigations into the origins of our universe.
Cryogenic temperatures are also used in electron microscopy to image frozen-hydrated specimens. This tool called cryo-electron microscopy achieves molecular resolution and enables to study fine cellular structures, viruses or proteins. The sample specimen remains in their native state without the need of any dyes or fixatives to prepare the sample for viewing. Single-molecule localization microscopy carried out at cryogenic temperatures improves the localization precision by a factor of four due to increased photon counts (from reduced photo-bleaching). Researchers have further carried on probing proteins using cryogenic super-resolution microscopy. This “blinking in the cold” enables super-resolution correlated light and electron microscopy.
Also, low-temperature biology and medicine fall under the cryobiology purview. The temperature range of cryobiology study is from below the normal range (of the biological material or organism) to the cryogenic temperatures. It involves the preservation of various samples, freeze-drying of pharmaceuticals, the study of hypothermia, cold-adaptation of seeds, plants, and animals, and cryosurgery. In cryosurgery, liquid Nitrogen (b.p. 77.3 K) is used to destroy tumors, on skin or scalp, or internally via a cryo-probe. Cryopreservation is successful in preserving biological samples such as sperms, embryos, and oocytes, using supercooled liquid nitrogen (-210 °C / 63.15 K).
Applications of cryogenics also extend to the science of extending life post-death. Many people have signed up for projects by institutes such as The Alcor Life Extension Foundation and Cryogenics Institute, where post-death one may preserve the body in liquid nitrogen for a price (running to the tune of more than 0.1 million Euros!). This field is known as “cryonics” – the low-temperature preservation of a dead person with a foresight that scientific advances in future will resuscitate them!
References
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Cryogenics, Encyclopedia Britannica
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Ultralow Surface Temperatures in East Antarctica From Satellite Thermal Infrared Mapping: The Coldest Places on Earth
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Louis Paul Cailletet: The liquefaction of oxygen and the emergence of low-temperature research
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Volger, J. (1977). Cryogenics: A Critical Review. Interdisciplinary Science Reviews.
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William D. Phillips – Facts. NobelPrize.org. Nobel Media AB 2018.
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Viewpoint: A Boost in Precision for Optical Atomic Clocks
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Cryogenics – basics and applications
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Blinking in the cold
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Advances in cryopreservation: we are not frozen in time
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Space cryogenics
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Cryogenic Electronics
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Molecules form new state of matter
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