Neutron Scattering

get as heat, the rest is transported as released radiation to the target vicinity like moderators,
reflector and shielding or is converted into nuclear binding energy . Secondly, all materials bit
by protons (and fast neutrons) will suffer from radiation damage. Finally, the extremely short
proton pulses generate shock-like pressure waves in target and structural materials, which
may substantially reduce the target seivice life. In order to both keep average target temperaturcs
low and reduce specific radiation damage and loads due to dynamic effects from shock
waves, a solid rotating target is conceivable and bas been proposed for the ESS . As any solid
target has to be cooled, it will inevitably be "diluted" by the coolant, whereby the primary
source's luminosity will be diminished . One should therefore operate the target in its liquid
state avoiding an additional cooling medium. Radiation damage would be no longer a problem
wich the target, but of course with its container . Obviously, the refractoiy metals are excluded
due to their high melting points. So we are left with elements like lead, bismuth, the
Pb-Bi eutectic or - of course - mercury . In tact, mercury has been chosen for the ESS, because
it was also shown to exhibit favorable neutron yield conditions as presented in Figure 1 .4 .
Fig. 1 .4 Calculated axial leakage distributions offast neutronsfrom a lead-nefected
mercury target compared to waten cooled tantalum and tungsten targets, respectively .
The dimensions of a target along the beam path will reasonably be chosen according to the
range of the protons of given kinetic energy . For mercury and the ESS energy of 1 .33 GeV
this is about 70 cm . Lateral target dimensions are optimized so that the moderators are not too
far from the proton beam axis (solid angle!) . A typical target-moderator-reflector configuration
is depicted schematically in Figure 1 .5 .