- Done a few simulations to check the photon and electron background for elastic, inelastic and Moller scattering, with/without the Lintel. The setting in the simulation is the same as that listed in 12/01/2005 report, except the theta_max = 10.25 degree, and the window opening of the 0.5 m Lead shield wall has 2 cm clearance around the elastic electron envelope. The results are listed in table 1 and table 2. Also did several simulations to check the background with different clearance at the upper edge of the shielding wall window (clearance at the upper edge = 4, 6, and 8 cm). The results are listed in table 3 and 4, as well as a comparison to 2 cm clearance case.
In summary, using the lintel will reduce the background from Moller scattering while not changing the background from elastic and inelastic scattering. When opening the window upper clearance from 2 cm to 8 cm, the inelastic background increases while the background from elastic and Moller are around the same. Right now, we are running simulation to see whether a bigger window opening (16 cm clearance at the upper edge) will reduce the inelastic background.
Table 1. Background from elastic reaction, inelastic reactions, and Moller scattering with lintel (without lintel), photon energy > 5 MeV, 2 cm clearance.
Reaction Photon Background (deposited energy > 5 MeV) Photon Background (deposited energy > 5 MeV, from collimator region only) Electron Background (energy > 5 MeV) ep elastic 0.2% (0.24%) 0.005% (0.037%) ep inelastic 0.014% (0.017%) 0.0001% (0.0006%) 0.041% (0.037%) Moller 0.15% (0.42%) 0.007% (0.28%) 0.12% (0.18%)
Table 2. Background from elastic reaction, inelastic reactions, and Moller scattering with lintel (without lintel), photon energy > 0.5 MeV, 2 cm clearance.
Reaction Photon Background (deposited energy > 0.5 MeV) Photon Background (deposited energy > 0.5 MeV, from collimator region only) ep elastic 0.91% (1.1%) 0.05% (0.28%) ep inelastic 0.11% (0.11%) 0.001% (0.006%) Moller scattering 1.1% (3.11%) 0.29% (1.87%)
Table 3. Comparison of background from elastic reaction, inelastic reactions, and Moller scattering for different clearance at the upper edge of the shielding window (upper edge clearance =2, 4, 6, 8 cm, lower edge clearance = 2 cm, with lintel) and photon energy > 5 MeV.
Reaction Photon Background (deposited energy > 5 MeV) Photon Background (deposited energy > 5 MeV, from primary collimator region only) Electron Background (energy > 5 MeV) Upper edge clearance ep elastic 0.2% 0.005% 2 cm ep elastic 0.2% 0.0015% 4 cm ep elastic 0.2% 0.0015% 6 cm ep elastic 0.22% 0.0046% 8 cm ep inelastic 0.014% 0.0001% 0.041% 2 cm ep inelastic 0.023% 0.00013% 0.08% 4 cm ep inelastic 0.022% 0.00015% 0.084% 6 cm ep inelastic 0.02% 0.000024% 0.083% 8 cm Moller 0.15% 0.007% 0.12% 2 cm Moller 0.12% 0 0.17% 4 cm Moller 0.15% 0.082% 0.14% 6 cm Moller 0.16% 0.015% 0.15% 8 cm
Table 4. Comparison of background from elastic reaction, inelastic reactions, and Moller scattering for different clearance at the upper edge of the shielding window (upper edge clearance =2, 4, 6, 8 cm, lower edge clearance = 2 cm, with lintel), photon energy > 0.5 MeV.
Reaction Photon Background (deposited energy > 0.5 MeV) Photon Background (deposited energy > 0.5 MeV, from primary collimator region only) Upper edge clearance ep elastic 0.91% 0.005% 2 cm ep elastic 0.88% 0.029% 4 cm ep elastic 0.9% 0.035% 6 cm ep elastic 0.86% 0.032% 8 cm ep inelastic 0.11% 0.0017% 2 cm ep inelastic 0.15% 0.0007% 4 cm ep inelastic 0.16% 0.0016% 6 cm ep inelastic 0.16% 0.0008% 8 cm Moller 1.1% 0.29% 2 cm Moller 1.04% 0.4 4 cm Moller 1.1% 0.46% 6 cm Moller 1.03% 0.42% 8 cm
- Figures of the source vertices of electron and photon background and their energy spectrum for different window size (upper edge clearance = 2, 4, 6, 8 cm).
2 cm clearance, without lintel 2 cm clearance, with lintel 4 cm clearance, with lintel 6 cm clearance, with lintel 8 cm clearance, with lintel
- Sample trajectories of electrons and photons for elastic, inelastic, and moller scattering (with lintel, 2 cm clearance).
- Electron and photon (deposited energy > 5 MeV) separation at Z=-80 for theta_max=10.25. This information is used to design a lintel made of tungsten with size of 5.25 cm thick (z), 16 cm high (x), and 56 cm long (y). The upstream face of the lintel is at Z = -80 cm, and x = 118 to 134 cm.
- 3D view of the upstream spectrometer from the quartz bar
View from the center of the lower edge of the quartz bar. 
View from the left end of the lower edge of the quartz bar. 