Page 221 - Neutrons for Sciences and Society

Neutrons are even more useful if one uses polarised beams, that is to say where all their magnetic spins are parallel. There are many methods to produce such beams. I have presented some of them briefly in chapter 3 on the use of neutrons. When they are polarised it is possible to reverse the direction of polarisation.
By measuring the scattering of polarised neutrons in these two opposite senses the distribution of magnetisation in the sample can be studied. It is hence possible to determine what are the origins of magnetism in organic matter which contains no metals. It is also possible to understand the giant magnetocaloric effect in certain substances where the temperature falls by more than
5 C when they are demagnetised. [2018 addition: This effect
had its first practical application in 2015 for the production of refrigerators with energy savings of up to 50% and using no polluting gas.] There are other aspects of magnetism which are important for technology. We know that computer memories make use of magnetisation and demagnetisation of small domains. The smaller these domains are, the higher is the storage capacity. Here too, neutrons can provide useful information.
Magnetism is not the only area where the work done at the ILL contributes to technology. One example: we know that hydrogen is under consideration as a substitute for petrol. Firstly there are many problems to resolve. One of these is the storage of this gas. A Swiss group led by Professor Yvon at Geneva has studied the use of metal alloys which can absorb great quantities of hydrogen. The ideal material has not yet been found. The diffraction of neutrons is perfect for studying these substances full of hydrogen.
Conclusion - An appraisal
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