Photon and Electron Background Study (2)

• Done more simulations to check the photon and electron background for elastic, inelastic and Moller scattering for three cases:
  (1) Double the height of the lintel. The size of the lintel was changed from 5.25 cm (thick) x 16 cm (high) x 56 cm (wide) to 5.25 cm (thick) x 32 cm (high) x 60 cm (wide), and its location is still at Z = -80 cm.
  
  (2) With the above new lintel design, cover the lips of the shield wall opening with 4 cm thick tungsten.
  
  (3) Without the lintel, and use the VT "finial" primary collimator design (21.86 cm thick primary collimator at the original location). The shield wall design is the same as case (2)
  
  The theta_max in case (1) and (2) is 10.25 degree, but it is 10.53 degree for case (3). We require the shield wall window having a 2 cm clearnace around the elastic electron envelope. Table 1 shows the simulation results and a comparison to the result we got in the last report (case 0, lintel size is 5.25 cm (thick) x 16 cm (high) x 56 cm (wide), and without 4 cm thick tungsten around the shield wall window).
  
  In summary, when using the VT "final" primary collimator, the electron and photon background is larger than other three cases. By moving the collimator 25 cm upstream, using a smaller theta_max and a lintle, we can greatly reduce the electron and photon background from moller scattering and the electron background from the inelastic scattering. When double the size of the lintel and uses a tungsten lips covering the shield wall opening, it can further reduce the background from moller scattering, but the inelastic electron background increases (why?).
  
  Table 1. Background from elastic reaction, inelastic reactions, and Moller scattering, 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)	Case #
  ep elastic	0.2%	0.005%		0
  ep elastic	0.22%	0.003%		1
  ep elastic	0.2%	0.003%		2
  ep elastic	0.24%	0.031%		3
  ep inelastic	0.014%	0.0001%	0.041%	0
  ep inelastic	0.021%	0.00015%	0.075%	1
  ep inelastic	0.015%	0	0.11%	2
  ep inelastic	0.015%	0.0015%	0.12%	3
  Moller	0.15%	0.007%	0.12%	0
  Moller	0.11%	0.03%	0.05%	1
  Moller	0.073%	0.016%	0.1%	2
  Moller	0.52%	0.41%	0.12%	3

  
  
  
• Figures of the source vertices of electron and photon background and their energy spectrum for the above simulations.
  
  

  2 cm clearance, with lintel

  2 cm clearance, with double size lintel

  2 cm clearance, with lintel, 4 cm tungsten lips around the shield wall window

  2 cm clearance, without lintel, VT primary collimator, 4 cm tungsten lips around the shield wall window