- Added a 0.5 m thick Lead shield wall at Z = 312.21 - 362.21 cm in GEANT simulation to reduce the molller electron background (and photon background) as shown in 11/10/2005 report. The opening of the window was designed according to the elastic electron x-y profiles at Z=312.21 cm and 362.21 cm. Also, in the simulation, the GLOB volume is filled with air, except at the region where the collimates are located (Z=-583.410 to Z=-256.619 cm, based on Allena's KEEPOUT Zone web page). The collimators region is filled with helium. The purpose of the unrealistic shield wall ($1M in Lead) is to allow us to study sources of upstream background while generating a minimum of new sources in the shield wall. In particular, without the shield wall, we had the problem that very low energy electrons generated by the Moeller beam were getting past the QTOR and hitting the detectors. For the same reason, I replaced the Helium with air in some locations.
Below are the simulation results for elastic, inelastic, and Moller scattering for theta_max = 10.03 (with lintel, window opening having 1 cm clearance around the elastic electron envelope), and theta_max = 10.53 (without lintel, window opening having 3 cm clearance around the elastic electron envelope).
Table 1. Background from elastic reaction, inelastic reactions, and Moller scattering.
Reaction Photon Background (deposited energy > 5 MeV) Photon Background (deposited energy > 0.5 MeV) Electron Background (energy > 5 MeV) Theta_max (degree) Clearance of Window Opening Lintel ep elastic 0.2% 0.94% 10.03 1 cm Yes ep elastic 0.22% 0.99% 10.53 3 cm No ep inelastic 0.014% 0.1% 0.05% 10.03 1 cm Yes ep inelastic 0.011% 0.09% 0.042% 10.53 3 cm No Moller scattering 0.065% 1.16% 0.094% 10.03 1 cm Yes Moller scattering 0.33% 3.20% 0.14% 10.53 3 cm No
1. Background from ep elastic reaction (the blue lines show the edge of the primary collimator opening).
Source vertices of photons, deposited energy > 5 MeV, theta_max=10.03 Source vertices of photons, deposited energy > 0.5 MeV, theta_max=10.03 
Trajectories of elastic electrons (red) and photon (blue), theta_max = 10.03 
Source vertices of photons, deposited energy > 5 MeV, theta_max=10.53 Source vertices of photons, deposited energy > 0.5 MeV, theta_max=10.53 
2. Background from ep inelastic reaction (the blue lines show the edge of the primary collimator opening).
Source vertices of photons, deposited energy > 5 MeV, theta_max = 10.03 Source vertices of photons, deposited energy > 0.5 MeV, theta_max = 10.03 
Source vertices of electrons, energy > 5 MeV, theta_max = 10.03 Trajectories of inelastic electrons (red) and photon (blue), theta_max = 10.03 
Source vertices of photons, deposited energy > 5 MeV, theta_max = 10.53 Source vertices of photons, deposited energy > 0.5 MeV, theta_max = 10.53 
Source vertices of electrons, energy > 5 MeV, theta_max = 10.53 
3. Background from Moller scattering (the blue lines show the edge of the primary collimator opening).
Source vertices of photons, deposited energy > 5 MeV, theta_max=10.03 Source vertices of photons, deposited energy > 0.5 MeV, theta_max = 10.03 
Source vertices of electrons, energy > 5 MeV, theta_max = 10.03 Trajectories of Moller electrons (red) and photon (blue), theta_max = 10.03 
Source vertices of photons, deposited energy > 5 MeV, theta_max = 10.53 Source vertices of photons, deposited energy > 0.5 MeV, theta_max = 10.53 
Source vertices of electrons, energy > 5 MeV, theta_max = 10.53 