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Chapter 3 - Why invest so much money in a source of neutrons?
molecular vibrations but other movements in matter being much less energetic, many efforts were made to improve the energy resolution of instruments. The back-scattering technique (see the end of ยง6.1) gives an improvement of 100 to 1000. Spin-echo goes even further and thus was the first technique able to observe the very slow motion of macromolecules.]
Neutron spin-echo is an ultra-sensitive method which, alone, allows measurement of very slow motions like the reptation of macromolecules. This wriggling motion was proposed by Pierre- Gilles de Gennes to explain the behaviour of polymers, and the first definitive experimental confirmation came from neutron spin- echo measurements60.
In practice scientists rarely use a single method to observe the dynamics of matter, and they try and cover the largest possible energy range (speed of motion) by combining inelastic scattering measurements from triple axis spectrometers, backscattering spectrometers, and spin-echo, but also inelastic scattering of X-rays.
3.3 Nuclear and Fundamental Physics
The nuclear physics experiments based around a reactor relate partly to the study of fission. Fission products are analysed to determine their mass and charge. Other experiments study the
60 D. Richter et al. (1990) Phys. Rev. Lett. 64, 1389-1392, DOI 10.1103/PhysRevLett.64.1389 66
