Pedro Arce Introducción a GEANT4 1 GAMOS tutorial Compton Camera Exercises

Pedro Arce Introducción a GEANT4 2 Compton Camera Simulation Exercises Ex. 1: Define Compton camera geometry Ex. 2: Obtain information about what is happening in the simulation Ex. 3: Apply Detector effects The exercises are sequential Use the commands of the previous exercise (only change what is indicated)

Pedro Arce Introducción a GEANT4 3 Compon Camera Exercise 1a: Compton geometry Scatterer: 0.5 cm X 0.5 cm X 1 cm Si crystal Absorber: 0.5 cm X 0.5 cm X 2 cm CZT crystal 12 x 12 crystals in 1 block in each ring 2 cm separation between scatterer ring and absorber ring Source of 141 keV photons at (0,0,0) towards the X axis, 5 cm from scatterer ring

Pedro Arce Introducción a GEANT4 4 Compton Camera Exercise 1b: use gamma source in water Place gamma source homogeneously distributed in a water sphere Activity: 1 milliCurie Energy: 141 keV

Pedro Arce Introducción a GEANT4 5 Compton Camera Exercise 2a: obtain information Make info about the physics processes that occur Make the crystal sensitive detector and produce signals (hits) Obtain histograms about hits quantities (energy, position, …) Get detailed info about Compton and Photoelectric effect in crystals

Pedro Arce Introducción a GEANT4 6 Compton Camera Exercise 2b: standard physics Use GEANT4 standard electromagnetic package, instead of low energy electromagnetic package Observe differences in energy distribution Observe differences in processes occurring Observe differences in CPU time

Pedro Arce Introducción a GEANT4 7 Compton Camera Exercise 2c: Classify events as Compton Imaging events A Compton imaging event is defined as one that has at least one signal in at least one scatterer crystal and one absorber crystal, with a summed energy approximately equal to the source energy Classification is done looking at the reconstructed hits Define a RecHitBuilder that builds hits for each crystal and defines the position as the centre of the pixel Count % of Compton imaging events How many are true single single events? How many have more than 2 reconstructed hits?

Pedro Arce Introducción a GEANT4 8 Compton Camera Exercise 3a: Energy resolution Set the photopeak energy gate as 1% Observe differences in number of Compton imaging events

Pedro Arce Introducción a GEANT4 9 Compton Camera Exercise 3ai: Energy resolution Set the photopeak energy gate as 1% Set the scatterer detector energy resolution as 1% Observe differences in number of Compton imaging events Observe differences in hits energy

Pedro Arce Introducción a GEANT4 10 Compton Camera Exercise 3aii: Energy resolution Set the photopeak energy gate as 1% Set the absorber detector energy resolution as 5% Observe differences in number of Compton imaging events Observe differences in hits energy

Pedro Arce Introducción a GEANT4 11 Compton Camera Exercise 3aiii: Energy resolution Set the photopeak energy gate as 1% Set the scatterer detector energy resolution as 1% AND the absorber detector energy resolution as 5% Observe differences in number of Compton imaging events Observe differences in hits energy

Pedro Arce Introducción a GEANT4 12 Compton Camera Exercise 3bi: Dead time Set the dead time of scatter detector crystals as 1 microseconds When a crystal takes signal, the full 12x12 crystal array becomes dead for a time Observe differences in number of Compton imaging events

Pedro Arce Introducción a GEANT4 13 Compton Camera Exercise 3bii: Dead time Set the dead time of absorber detector crystals as 1 microseconds When a crystal takes signal, the full 12x12 crystal array becomes dead for a time Observe differences in number of Compton imaging events

Pedro Arce Introducción a GEANT4 14 Compton Camera Exercise 3biii: Dead time Set the dead time of scatterer and absorber detector crystals as 1 microseconds When a crystal takes signal, the full 12x12 becomes dead for a time Observe differences in number of Compton imaging events

Pedro Arce Introducción a GEANT4 15 Compton Camera Exercise 3ci: Measuring time Set the measuring time of the scatterer detector crystals as 1 microseconds Two signals in a crystal cannot be distinguised if they differe less than a given amount Observe differences in number of Compton imaging events

Pedro Arce Introducción a GEANT4 16 Compton Camera Exercise 3cii: Measuring time Set the measuring time of the absorber detector crystals as 1 microseconds Two signals in a crystal cannot be distinguised if they differe less than a given amount Observe differences in number of Compton imaging events

Pedro Arce Introducción a GEANT4 17 Compton Camera Exercise 3cii: Measuring time Set the measuring time of the scatterer and absorber detector crystals as 1 microseconds Two signals in a crystal cannot be distinguised if they differe less than a given amount Observe differences in number of Compton imaging events

Pedro Arce Introducción a GEANT4 18 Compton Camera Exercise 2c: Using events with multiple interactions Compton imaging is done on 2 detector events, so when there are multiple interactions within a detector event it is necessary to identify the position and energy of the interaction of interest, to reduce to one interaction in each detector This can be achieved via “Identifying Compton Interactions” using various algorithms It may be appropriate to use the interaction energy, position or separations to identify the 1st interaction.

Pedro Arce Introducción a GEANT4 19 Compton Camera Exercise 3a: Using events with multiple interactions Set the ComptonRecHitDist for the scatterer and absorber to 0 mm. /gamos/setParam CC:EvtClass:ComptRecHitDistScat 0.*mm /gamos/setParam CC:EvtClass:ComptRecHitDistAbs 0.*mm Use the NM1stHitByEnergy Algorithm Only single/singles will be identified Write out singles using /gamos/setParam CC:EvtClass:DumpSingles 1 /gamos/setParam CC:EvtClass:DumpMultiples 0 Observe number of Compton imaging events

Pedro Arce Introducción a GEANT4 20 Compton Camera Exercise 3b: Using events with multiple interactions Set the ComptonRecHitDist for the scatterer to 6 mm and absorber to 0 mm. /gamos/setParam CC:EvtClass:ComptRecHitDistScat 6.*mm /gamos/setParam CC:EvtClass:ComptRecHitDistAbs 0.*mm Use the NM1stHitByEnergy Algorithm Only multiples/singles and singles/multiples will be identified Write out only the multiples using /gamos/setParam CC:EvtClass:DumpSingles 0 /gamos/setParam CC:EvtClass:DumpMultiples 1 Observe number of Compton imaging events

Pedro Arce Introducción a GEANT4 21 Compton Camera Exercise 3c: Using events with multiple interactions Set the ComptonRecHitDist for the scatterer to 0 mm and absorber to 6 mm. /gamos/setParam CC:EvtClass:ComptRecHitDistScat 0.*mm /gamos/setParam CC:EvtClass:ComptRecHitDistAbs 6.*mm Use the NM1stHitByEnergy Algorithm Only singles/multiples and singles/multiples will be identified Write out only the multiples using /gamos/setParam CC:EvtClass:DumpSingles 0 /gamos/setParam CC:EvtClass:DumpMultiples 1 Observe number of Compton imaging events

Pedro Arce Introducción a GEANT4 22 Compton Camera Exercise 3d: Using events with multiple interactions Set the ComptonRecHitDist for the scatterer to 6 mm and absorber to 6 mm. /gamos/setParam CC:EvtClass:ComptRecHitDistScat 6.*mm /gamos/setParam CC:EvtClass:ComptRecHitDistAbs 6.*mm Use the NM1stHitByEnergy Algorithm Multiples/multiples, singles/multiples, multiples/singles and singles/multiples will be identified Write out only the multiples using /gamos/setParam CC:EvtClass:DumpSingles 0 /gamos/setParam CC:EvtClass:DumpMultiples 1 Observe number of Compton imaging events

Pedro Arce Introducción a GEANT4 23 Compton Camera Exercise 3d: Using events with multiple interactions Set the ComptonRecHitDist for the scatterer to 0 mm and absorber to 6 mm. /gamos/setParam CC:EvtClass:ComptRecHitDistScat 0.*mm /gamos/setParam CC:EvtClass:ComptRecHitDistAbs 6.*mm Use the NM1stHitByXYZPos Algorithm singles/multiples will be identified Write out only the multiples using /gamos/setParam CC:EvtClass:DumpSingles 0 /gamos/setParam CC:EvtClass:DumpMultiples 1 Observe number of Compton imaging events