Page 129 - Neutrons for Sciences and Society

Chapter 5: The construction of the reactor and the scientific groups
everything is done to ensure that no oxygen can come in contact with the hydrogen, avoiding formation of a potentially explosive mixture. However if such a mixture is formed the walls will resist a pressure of 19 bars, which is the pressure of a detonation wave. The presentation of the ILL reactor at the Santa Fe conference included the cold source with deuterium liquid already foreseen. It was this component of the reactor which was then the subject of the largest number of questions which demonstrated certain scepticism among some participants. It was a radically different choice from the British project which sought to minimise the volume of liquid hydrogen in the interior of the reactor. The results showed that there was no basis for this scepticism.
The reactor also included a hot source which amplifies the flux of neutrons with energies between 0.15 and 1 eV. Paul Ageron was not directly involved in its construction. The study was carried
out by the GfK at Karlsruhe in collaboration with the project group, and the manufacture was entrusted to Heraeus. It consists of a graphite cylinder 20 cm in diameter and 30 cm high which is heated to 2000 K (about 1730 °C) by radiation; three horizontal and one inclined beam tube are pointed at the source. The utility of the hot and cold sources to change the neutron spectrum is shown in Fig. 5.10. The location of these devices in the reflector tank is shown in Fig. 5.11.
Neutron guides are of fundamental importance at the ILL, and have been in use from the start of the reactor providing 40% of the possible locations for instruments. Since the installation of the second cold source this fraction has further increased. The principle was discovered more or less by
120