# G4Beamline PbBi

Development of a Positron source using a PbBi converter and a Solenoid

# Conclusions

1. A 0.3 (0.6) Tesla Solenoid with a diameter to allow a 9.74 (3.94) cm diameter pipe would collect a positron per thousand incident electrons on a 2mm thick LBE target with 0.25 mm thick SS windows.
2. A 15 cm long, 0.2 Tesla solenoid with a 3.94 diameter beam pipe would collect a positron per two thousand electrons impinging a 2mm thick LBE target with 0.25 mm thick SS windows.
3. A 4 Tesla Solenoid will remove beam pipe heating from scattered electrons downstream of the target when using a 3.94 cm diameter beam pipe.

# Reports

## Niowave_6-2016

1.) Create a positron (10,000 positrons) and electron event file containing t,x,y,z,Px,Py,Pz for positrons exiting the solenoid and an incident Gaussian beam 1cm in diameter and with a sigma of 1cm.

compare distributions with and without solenoid.

2.) Determine the back ground when using a 3.48 diameter beam pipe and Solenoid field of 0.2 for a NaI detector placed at

3.) Experiment, install dipole and solenoid in the tunnel.

# Solenoid

## Solenoid Map

Length =

Current=

Magnetic Field Map in cylindrical coordinates (Z & R) from Niowave

# Rear Window Thickness

Question: Will a thicker downstream exit window increase the positron production efficiency by providing more material for a brehm photon to pair produce in?

Positrons were counted exiting a ideal 0.2 Tesla solenoid that was 15 cm long. A ten MeV electron beam with a 0.5 cm cylindrical radius impinged a 2mm thick PbBi liquid target that had a surface area of 2.54 cm x 2.54 cm. A 0.25 mm thick stainless steel entrance window was used.

Target is at -106 mm, entrance SS window is at -108.25 mm , exit SS window is at -103.75 mm, A sensitive detector for positron is placed at Z= +44mm. The sensitive detector is a cylinder of radius 11.74 cm.

 SS Exit WIndow Thickness (mm) Positrons/Million electrons 0.0 1142,1096,1149,1073,1083 = 1109 +/- 35 0.25 774,836,800,785,798 = 798 +/- 23 0.5 693,704,713,697,715 = 704 +/- 10 1.0 587,606,548,592,550 =577 +/- 26

Conclusion 1
Positron production efficiency improves when the exit window is made thinner
Conclusion 2
You loose about 28 +/- 4 % of the positrons in the 0.25 mm thick SS exit window.

# Background studies

## Brem Spectrum

Below is the photon energy distribution (from Brem & pair production) using a 2mm Pb target for two different incident electron energies; 6 and 10 MeV. The photons are 1 cm downstream of the target and intersection a large forward region.

insert photon spacial distributions


Now move the scoring region downstream to a position representing the location of a NaI detector.