11.3 Radiation from the Synchrotron
Shielding of the MICE area from beam loss in the proton synchrotron:
Proton beam cannot directly enter the MICE beam line due to any of the ring magnets being
off or incorrectly steered. The worst case situations occur when the beam is lost with the
dipole in super-period 7 off: The beam then strikes the body of the dipole in sp7: Point A; or
with the beam lost in a quad close to the MICE beam exit: point B. Any other fault looses the
beam away from MICE, or at a lower level. Here, it is assumed that full beam intensity of
3x1013 proton is lost for 10 consecutive pulses at 800 MeV.
Additionally, the synchrotron beam is at a height of 1.4m and the MICE beam line at a height
of 1.8 m. An aperture “MICE-hole” of 0.65 m diameter is to be made to communicate
between the synchrotron vault and the MICE hall. This limits the opportunity for beam to be
directly scattered into the MICE hall.
Geometrical Model:
Beam loss at points A or B can be conservatively modelled by a point loss at a distance equal
to the closest approach of the beam to the wall to hall 5.2. The MICE-hole is taken as being
square to the wall. The MICE-hole will be filled with lead shot to make as tight a fit to the
nose of the solenoid as possible. Although the outside can be packed, a major aperture of the
bore of the magnet (30cm diameter) remains. The MICE-hole is approximately 1.2 m (4ft)
deep through the concrete wall between the vault and hall 5.2.
Shielding on the hall 5.2 side of the joining wall can be used to obtain the correct shield
thickness to limit the dose from a complete beam spill to 0.1 Sv where the line between the
spill and the dosed body is through continuous concrete and steel. Where the line passes
through the solenoid aperture, then the shielding needs to be provided at a larger distance, and
barriers provided to prevent persons passing through the synchrotron side of this line.
A
B
Figure 11.3-1. Schematic of the beam line and synchrotron showing the possible loss points.
Lc
Ls
Lw
Lse
La
Figure 11.3-2. Geometery of the shielding of the MICE hall from beam spill in the
synchrotron.
From the sketch of the geometry, the MICE beam elements in the vault do not provide
shielding. Away from the MICE-hole, the existing concrete needs to be supplemented by 2m
of steel.
Where the shielding is weak, i.e. in line with the bore of the solenoid, calculations show that 2
m of steel should be added as a “beam dump”. The steel should ideally be complemented by
concrete to absorb low energy neutrons.