Light Guide Design
Requirements
Given the dimensions of the individual paddles of 60mm x 2.54mm x 2520mm and the dimensions of the photo multiplier tube (PMT) including necessary magnetic shielding it is necessary to have light guides. Further arguments for the use of light guides are the rectangular shape of the paddle cross section versus the round shape of the PMT entrance window that does not favor a direct coupling of the readout to the scintillator. In addition particles that pass very close to the end of the paddle would generate a disproportionate large signal in the PMT because of the highly non linear light absorption at short distances for short wave lengths (UV). The PMT H10534 is a 10 stage tube with a quoted 2 inch window. Measurements indicate a total diameter of the tube of 50mm. The H10534 is a full assembly including shielding and base as received from the manufacturer. At this point this assembly has an outer diameter of 60mm. Because of the expected high magnetic field in the region of the PMT of the order of 100 Gauss additional iron shielding is necessary. At this point a total outer diameter including such a shielding is estimated to be of the order of 66mm. As a consequence this dimension becomes larger than the paddle height of 60mm requiring the light guide to be bend in order the provide enough space to tack the paddles on top of each other.
Stacking of Paddles
- The following picture shows the situation with having 66mm outer diameter readout systems coupled to the end of 60mm high paddles in terms of space as viewed for the end. Media:tof_paddle_setting.pdf
