Defining a uranium contaminated soil with GPS

[Guidepast]

Hello to all, I’m a student new to Geant4,
I have created a trapezoid representing uranium contaminated soil (Logical Volume name: Soil) in order to analyse the efficiency of my HPGe detector design, I would like to distribute the particle source through all the soil volume, for that I’m using the following commands:

/gps/pos/type Volume
/gps/pos/confine Soil
/gps/ene/mono 185.7 keV
/gps/particle gamma
/gps/ang/type iso

But when I run it, the particles are not distributed, (image attached) . Any hints on how should I deal with this?

Thank you very much in advance.

[Andrea]

Hello,

You have to define a volume in which the GPS must generate the primary vertexes (/gps/pos/shape) and then confine them to the physical volume, like this:

/gps/pos/type Volume
/gps/pos/shape Para
/gps/pos/centre 0. 0. 0. cm
/gps/pos/halfx 10. cm
/gps/pos/halfy 10. cm
/gps/pos/halfz 10. cm
/gps/pos/confine Soil

Andrea