Hi everyone,

we had a problem when calculating the number of particles (geantinos) hitting some volumes.

We created an isotropic homogeneous radiation field inside a sphere. (For space simulations.)

Based on the descriptions about GPS, the following macro seemed appropriate:

```
/gps/particle geantino
/gps/pos/type Surface
/gps/pos/shape Sphere
/gps/pos/radius 250 mm
/gps/pos/centre 0 0 0 mm
/gps/ang/type cos
/gps/ang/mintheta 0 deg
/gps/ang/maxtheta 90 deg
```

However when checking the number geantinos hitting some (geometrically) identical volumes with different positions, we’ve got very different hit numbers. (E.g. 1925, 2197, 2092, 692, 755, 766.)

Our geometry was in GDML converted from CAD files, thus there were tiny overlaps between the volumes. (Every volumes’ mother was the world volume, there were no subvolumes.)

Note: our geometry consists of thin Si detectors with the necessary (simplified) electronics+casings. Its in the order of 10-20 cm in total (the smallest components has a size of a few cm), and the maximal overlaps was around 500 microns.