was first liquefied in 1908 by Heike Kamerlingh-Onnes
. It has a boiling point
of 4.2 kelvin
). It can also be cooled to a lower temperature
. A powerful pump
is used to remove the vapour
and the liquid evaporate
s off. Therefore the helium is reduced down to a temperature of around 1.2 K
For a higher price however, helium three
can be used. This has two proton
s, but unlike helium four
has 1 neutron
rather than two. This enables the temperature
to be reduced down to around 0.3 K.
Through the further race to get down as close to absolute zero, (0 K), developments of a dilution refrigerator are in use, enabling temperatures of as low as 0.002 K (2 millikelvin)
and now an update!
I have been reliably informed (I think) by thornton that the lowest temperature on record is ...and I quote...
'with the advent of laser trapping and cooling, the lowest temperature on record is now in the nanokelvin (10^-9 K) range'