PPT Slide
Pion target - induced activity - the case for using Mercury (Helge Ravn)
The extremely high induced activity levels may well provide the overriding reason for the use of a mercury jet target.
The specific activity is greatly reduced compared to a fixed target (the ‘band-saw’ target is somewhere between the two).
In addition, as proposed by Helge Ravn, the mercury would be distilled to remove most non-volatile spallation products. Volatile products would also be removed from the target area into filters or tanks.
This would leave open the possibility of manual intervention in case of catastrophic failure of the target or magnet system in the production area.
Note: In 1985 CERN AA was testing rhenium production targets in air-cooled steel containers. The beam fluence was 4.2 1012 protons s-1 (500 times less than that proposed for the muon collider pion source) Two containers failed after a few days of use distributing spallation products into the Target Area (maintained under reduced pressure for containment). After a 20-day cool-down period the area was decontaminated under the supervision of radiation protection specialists (a cine film was made). The total personnel radiation dose was 6.5 rem distributed between 92 persons participating in the clean-up.