1. Single Planar Detector Monte Carlo Simulations Andrew Mather arm@ns.ph.liv.ac.uk

2. Introduction - Simulation Simulations run of a single 6 x 6 x 2 cm Germanium crystal. Point isotropic source @ 10cm from the front face of the crystal, 10 million gamma’s emitted. (100-1000 keV step 10 keV) The same (geometric wise) simulation reproduced in GEANT 4 & MCNP [G.Turk]. Both simulations output all interaction positions and energies in the same format. Results produced from this file for both codes using the same analysis software (Java).

3. Introduction - Packing The analysis program uses a packing algorithm that packs any interaction points closer together than a specified amount into a single point. Packing is used to make simulated results more comparable to real detectors. Takes the average positions of the points to be packed and a sum of the energy deposited at each point. Using 1mm currently as the maximum distance apart two interactions have to be for a “real” detector to be able to resolve them as two individual interactions.

5. Event defined as a gamma ray depositing some energy in the detector. Interactions can be Compton or Photoelectric. @ 511 keV Photo-peak events = ~ 2.5 interactions

6. Full energy event is an event where all the energy is deposited in the detector. @ 511 keV : Geant = 29% MCNP = 36%

7. First Interaction – The actual first time the gamma-ray interacts. Main Interaction – The interaction depositing the most energy. @ 511 KeV : 70% of the time the first interaction = main interaction

8. When the first interaction isn’t the main interaction – What is the average distance between the two? (Important to know if we make the assumption on real data to give and idea of how the imaging will be affected as a result)

9. Point Source Detector First Interaction Main Interaction Definition of Angle θ

10. ~ 8.7mm perpendicular from line joining source and first interaction position.

11. Current & Future Work Simulation with two planar detectors and back to back 511 keV emitting source. Look at imaging from interaction position file using both first interaction is the main interaction assumption and with the true first interaction. 2D Image reconstruction using BPGeant 4 visual of two detectors Image reconstruction from Geant 4 data