Beryllium sphere's purpose

I love this movie (to the extent that we made thermion outfits for a fancy dress once ).  I've always pondered what the beryllium sphere was actually for.  Reading around, a number of possibilities for this are:

 A neutron reflector - beryllium is good for reflecting neutrons.
 A gamma reflector - beryllium is apparently fairly good at reflecting gamma rays too.
 Some kind of inertial system
 Affects the space-time continuum in a way suitable for warp drives.
 High temperature and pressure confinement system.

The reason I wonder is mainly because beryllium is an unusual material and is very toxic to handle, so they NSCA designers must have had some special reasons for such an exotic material.  The fact that an alien race produced a suitable replacement indicates it is practically a commodity in spacefaring communities.  Is there any data connecting the performance of beryllium spheres with that of transparent aluminium?