Add single-element test problems

[celeritas-project]

Add single-element test problems

[stognini]

New simplified CMS geometry

This set of single-element concentric cylinders acts as a spherical cow in a vacuum version of CMS. The gdml file is produced by and available in benchmarks/geant4-validation-app.

Composition

• The World volume is square box (G4Box) and its dimensions are expressed in cartesian coordinates [x. y, z].
• All other volumes are concentric cylinders (G4Tubs), and their dimensions are expressed as [inner radius, outer radius, length]
• A small distance between cylinder edges is defined to avoid overlapping and is currently set to be d = 1e-10 cm;

Volume	Composition	Dimensions [cm]
World volume	H (G4_Galactic)	[1000, 1000, 2000]
silicon tracker	Si	[30, 125, 1400]
electromagnetic calorimeter	Pb	[125, 175, 1400]
hadron calorimeter	C	[175, 275, 1400]
superconducting solenoid	Ti	[275, 375, 1400]
iron / muon chambers	Fe	[375, 700, 1400]

Each volume in the table can be seen (and is listed in the geometry scene) in the event display:

[sethrj]

Closed by #231 I think 😄