# Nuclear orientation
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'''Nuclear orientation''', in [nuclear physics](/source/nuclear_physics), is the directional ordering of an assembly of [nuclear spin](/source/nuclear_spin)s with respect to some axis in space.[[http://encyclopedia2.thefreedictionary.com/nuclear+orientation Nuclear orientation], ''[The Free Dictionary](/source/TheFreeDictionary.com)''.][[http://www.accessscience.com/abstract.aspx?id=459400 Nuclear orientation] {{Webarchive|url=https://web.archive.org/web/20110617073421/http://www.accessscience.com/abstract.aspx?id=459400 |date=2011-06-17 }}, ''[http://www.accessscience.com/ AccessScience]''.] It is one of the [nuclear spectroscopy](/source/nuclear_spectroscopy) methods.
A [nuclear](/source/Nuclear_physics) level with [spin](/source/Spin_(physics)) in a [magnetic field](/source/magnetic_field) will divide into magnetic sub-levels with an energy spacing.[[http://www-nog.physics.ox.ac.uk/www/gen/gen.html General Idea of Nuclear Orientation], [http://www-nog.physics.ox.ac.uk/ Nuclear Orientation Group], [University of Oxford](/source/University_of_Oxford), UK.]
The populations of these levels are determined by the [Boltzmann distribution](/source/Boltzmann_distribution) at a steady temperature and will essentially be equal. The exponential in the Boltzmann distribution should not be equal to 1 to obtain unequal populations. To achieve this, cooling to a temperature of around 10 millikelvin is needed.
Typically, this is achieved by implanting the [nuclei](/source/Atomic_nucleus) of interest into [ferromagnetic](/source/ferromagnetic) hosts.
In the mid-1940s, [Yevgeny Zavoisky](/source/Yevgeny_Zavoisky) developed [electron paramagnetic resonance](/source/electron_paramagnetic_resonance), eventually leading to the concept of nuclear orientation.[B. Bleaney and O. V. Lounasmaa, [https://www.jstor.org/stable/3557722 Nuclear Orientation and Nuclear Cooling Experiments in Oxford and Helsinki. Part 2. Progress from 1945 to 1970]. ''[Notes and Records of the Royal Society of London](/source/Notes_and_Records_of_the_Royal_Society_of_London)'', Volume 57, Number 3, pages 323–330, September 2003. Published by [The Royal Society](/source/The_Royal_Society).]
In the early 1950s, [Neville Robinson](/source/Neville_Robinson), [Jim Daniels](/source/Jim_Daniels_(physicist)), and [Michael Grace](/source/Michael_Grace_(physicist)) produced an example of nuclear orientation for the first time at the [Clarendon Laboratory](/source/Clarendon_Laboratory), [University of Oxford](/source/University_of_Oxford).[Nicholas Kurti, [https://www.independent.co.uk/news/people/obituary-neville-robinson-1354491.html Obituary: Neville Robinson]{{dead link|date=August 2021|bot=medic}}{{cbignore|bot=medic}}. ''[The Independent](/source/The_Independent)'', 27 November 1996.]
There is now a Nuclear Orientation Group at Oxford.