Radiation Levels

The following assumptions are made:
LHC operational year = 10⁷s
Luminosity = 2 x 10³²cm^-2s^-1
non-diffractive cross section = 80mbar (this is a bit pessimistic, current understanding: it is ~60mbar)
however, this would give 1.6 x 10⁷ interactions / second.

Regions of interest:

1. 8mm<r<45mm and -20cm<z<80cm
   The region of the silicon detectors is dominated by primary particles. The particle fluxes can be estimated using Pythia.
   In the optimization note , 1.5 particles / cm²  at r=8mm were found. Folding this with the NIEL constants, the displacement damage to the silicon in one year at the innermost radius is equivalent to 0.9 x 10¹⁴ 1 MeV neutrons/cm². To simulate this displacement damage with 25 GeV protons, about 1.8 x 10¹⁴ protons/cm² are needed.
   (This also corresponds to an absorbed dose in the silicon of about 18 MRad or 1.3kJoule).
2. r=50mm and -20cm<z<80cm, place of frontend chips:
   absorbed dose: 240 kRad / year
3. r=20cm, position of o-rings
   absorbed dose (silicon): 100 kRad/year
4. r=50cm, position of feedthroughs
   absorbed dose (silicon): 20 kRad/year
5. r=100cm, z<-100cm, position of turbo pumps
   absorbed dose (silicon): 20 kRad/year
6. at 10m distance, balcony, place of ECS receivers ...
   absorbed dose (silicon): <100 Rad /year, if necessary more shielding can be added to achieve this dose level.

These numbers should be seen as indicative and a safety factor of 5 should be applied. A more detailed study will follow, but not before the TDR. The absorbed doses are calculated for silicon. They might be different for other materials.

The link to the notes of Talanov can be found here:

• LHCb-2000-015, Estimation of absorbed dose levels at possible locations for LHCb detector

• LHCb-2000-013, Radiation environment at the LHCb inner tracker area

• LHCb-98-019, Radiation environment at the LHCb vertex detector

see also here for radiation damage in silicon