Cool Solution For Couples 

Fascinating aspects of matter unfold 
at very low temperature, reports Biplab Das 

Low temperature, as low as -200 °C, can bring out fascinating aspects of life. Physicists and biologists discussed those aspects in a workshop recently held at the Saha Institute of Nuclear Physics (SINP). The workshop, 'Cryogenics: Experiments and Applications', was organised by the Indian Physics Association (IPA). 

Dr. Jiban Kumar Duttagupta from SINP introduced the topic to the audience. "Cryogenics is a science which deals with the effect of extremely low temperatures on matter," he said. Protein crystals are preserved at those temperatures. Also, low temperature prevents growth of microbes and provides a sterile atmosphere for surgical instruments. 

Dr. S. K. Mitra from the Variable Energy Cyclotron Centre discussed the techniques for producing such low temperatures. "The method is the same one used in a refrigerator," he said. A gas is passed through a high-pressure chamber known as compressor. High pressure increases its temperature. The hot gas is then passed through a condenser where it gives off heat and turns liquid. The liquid is then passed through an expansion valve where it evaporates and turns to a gas. Evaporation absorbs heat and makes things cool. In the laboratory, nitrogen and helium are used to achieve temperatures of -185 °C and -269 °C respectively, said Mitra. 

"Liquid hydrogen and oxygen are used as fuels for launching spacecraft," said Dr. Santanu Dutta, vice president, IPA. Dr. R. G. Sharma from Nuclear Science Centre, New Delhi, focused on the role of liquid helium in superconductivity. On constant cooling helium becomes a superliquid at a temperature of about -273 °C. A material dipped in this liquid loses all its resistance and achieves 800 times the conductivity of copper wire. 

Liquid nitrogen plays a key role in deciphering the structure of proteins, said Dr. P. Sengupta from SINP. In extremely low temperatures, protein molecules emit light. "This phenomenon, known as luminescence, helps predict the structure of a protein," he said. Liquid nitrogen also helps preservation of embryos and blood. "Blood can be stored for about 34 days in a blood bank. In liquid nitrogen, it can be stored for as many as 34 years," said Dr. G. C. Majumdar from Indian Institute of Chemical Biology (IICB). 

According to him, low temperature plays a key role in sperm preservation. Adding a little glycerol to liquid nitrogen ensures longer preservation. Glycerol prevents formation of ice crystals inside the cells. "Ice crystals damage the membrane of preserved cells," he said. 

When preserved in liquid nitrogen and glycerol, sperm cells retain their ability to swim. This is a must when sperm cells are used for infertility treatment. In India, 40 million couples are suffering from infertility problems. "Low-temperature science is a boon to those couples," said Majumdar.