PMT-Reflector Geometry

The photomultiplier-reflector geometry is well described by a set of spheres, cylinders and tori. The exact geometry is discussed in the Programmer's manual; here it is merely sufficient to be aware that the PMT-reflector arrangement is divided into a number of regions (reference also Figure 12.5):

Figure 12.5: Schematic of the current PMT geometry implemented in SNOMAN. Note that the finite thickness glass envelope is not shown. The dimensions and construction lines are shown for reference only.

1. The rest of the detector. A book keeping region.

2. The region (either air or water) internal to the reflector, bounded by the reflector which may or may not have petals (users choice - see below), the front face of the photomultiplier and the exit into region 1.

3. The glass envelope of the tube, which has a thin photocathode on the upper inner surface and aluminium on the lower inner surface. The envelope is assumed to be geometrically symmetric and a uniform 3mm thick.

4. The internal volume of the photomultiplier. It includes a description of the dynode stack.

5. The rest of the PMT-reflector bucket (ie everyhting not in another region). Assumed to be opaque/black for the purposes of optical photon transport.

6. The pinout glass of the phototube. Presumed to be standard glass, but is defined as a separte region to allow for radioactivity studies.

7. The base of the phototube.

These are the only regions needed for tracking optical photons. Various of the boundaries have properties associated with them that may alter the photon's properties:

From	To Region
Region	1	2	3	4	5	6	7
1	-	In	-	-	-	-	-
2	Out	-	Fresnel	-	Omega	-	-
3	-	Fresnel	-	P-c or Al	Lost	Fresnel	-
4	-	-	P-c or Al	-	-	-	-
5	N/a	N/a	N/a	-	-	N/a	N/a
6	-	-	Fresnel	Fresnel	lost	-	Lost
7	-	-	-	-	N/a	N/a	-

Symbol	Meaning
-	No common surface
In	Interface from the main SNOMAN code.
Out	Interface to the main SNOMAN code.
Fresnel	Fresnel reflection and refraction is implemented.
P-c	Photocathode reflection, transmission or absorption may occur.
	In the event of the latter, the tube may record a hit.
Al	Reflection/absorption due to the aluminium coating the
	back hemisphere of the phototube.
Omega	The Omega may reflect or absorb the photon.
Lost	The photon enters region and is dumped.
N/a	Not applicable. Region is not transparent.

Of these possible interactions, fresnel reflections are covered elsewhere, the rest are covered below.