Page 22 - Neutrons for Sciences and Society

Neutrons for Science
and realised on BEPO by Peter
Egelstaff15 (Fig. 1.5). For a number of
experiments, especially spectrometry,
it is preferable to use long wavelength
(hence very low energy) neutrons,
4 Å or more. Theoretically it is easy
to increase the flux of these neutrons.
It is sufficient to introduce a quantity
of liquid hydrogen at the end of the
beam tube. In this medium neutrons
are thermalised to a mean temperature
of 20 K, increasing their wavelength.
The Saclay Group (Daniel Cribier and
Bernard Jacrot) impressed by these
results launched the construction of
a cold source for a new reactor (EL3) being built at Saclay. This work entailed a close collaboration with the low temperature laboratory of Grenoble, directed by Louis Weil, and in particular with Albert Lacaze. The cold source which operated from 1959 used a mixture of liquid hydrogen and deuterium which allowed the source to have a greater volume. I should note that I often met Peter Egelstaff during the construction and benefited from his constant help which was of great value. To gain time most of our meetings were often in the airports in London or Paris. Later cold sources were also installed in the German reactors in Karlsruhe and Jülich.
15 Butterworth I., Egelstaff P.A., London H., Webb F.J., Phil. Mag., (1957) 2, p917, DOI 10.1080/14786435708242730.
Fig. 1.5: Peter EGELSTAFF
13