Angular distribution for alphas in centre of mass and lab, and for 15O in lab.
Energy of 15O as a function of alpha energy
Angle of 15O as a function of alpha energy.
efficiency, as a function of positions of 2 detectors:
LEDA + S2
Two LEDAs: the more distant one is positioned so that its maximum angle is 1' less than the minimum angle of the near one.
The bottom line: although the efficiency increases from 43% to 50% for the LEDA at 50 mm as the S2 behind it moves from 25 mm behind to 5 mm behind, an efficiency of 53% is obtained for one leda at 62 mm and a second at 167 mm from the target. Moreover, for a minimum distance of 100 mm (consistent with TOF PID), LEDA+S2 has an efficiency of ~6%, whereas 2LEDA has an efficiency of ~44% (at 100 mm and 272 mm).
***Update***
Here's a figure showing the efficiency of two detector configurations for 5.7 MeV 18F.
The S2 is always 5 mm behind the LEDA; for the two-leda configuration, the positions are as follows:
forward backward
leda leda
30 90
40 120
50 150
60 180
70 210
80 241
100 303
120 366
140 430
160 495
180 561
200 629
(all in mm from the target)
