Exercise 6: Reducing the acceptance

Object: Observe the effect of detection acceptance, or solid angle.

Similar to Exercise 4 using the block and then the cylinder, but simply separate the target from the block by 500 cm. Do this for 50 MeV gammas.


VOL1 functions as a container for all other volumes of the simulation, and as such, it must also be modified when the geometry expands.  If you want to see the geometry or examine parts of it, use the interactive GEANT DRAW command with different values of U0, V0, SU, and SV (positioning of viewpoint and scaling factor), SHIFT command to simply shift the viewpoint, or ZOOM command for interactive placement.

Look for differences in results with Exercise 4.  With the block, there should be some similarity with the change from the block to the cylinder in Exercise 4.  When you consider the solid angle varies as the inverse square of the distance, this much of a change in separation between the target and the block is bound to have a large effect on the count rate of charged particles.  However, with the block remaining the same dimension, the shower containment is unchanged, so that by pulling the block back one finds that the energy resolution for gamma rays is retained while significantly reducing the charged background.

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