2.3 Prototype Tests
The setup is shown schematically in (fig. 2-5). The blocks of aerogel are stacked together and wrapped in a PTFE white diffusing box. On the bottom, the top and the middle plane, PMP dipped in PTFE foils is used to increase the light collection efficiency by shifting the wavelength of the Cerenkov light reaching the foils. The phototube is placed on top of the box, as shown in (fig. 2-5). This geometry has the following advantages:
| Box (cm3) | Aerogel (cm2) | Length (cm) | PMT (R5900U) | PMP foils | No p.e. | Simulation |
|---|---|---|---|---|---|---|
| 11x11x10 | 9.5x9.5 | 8 | 1,center | YES | 10.8 | 10.8[3] |
| 11x11x10 | 9.5x9.5 | 8 | 1,corner | YES | 10.0 | 9.5 |
| 11x11x10 | 9.5x9.5 | 8 | 1,corner | NO | 6.7 | |
| 11x11x10 | No | 0 | 1,corner | YES | 0.5 | 0.0 |
| 14.5x14.5x10 | 14.5x14.5 | 4 | 1,corner | YES | 4.3 | 3.9 |
| 15x15x10 | 15x15 | 10 | 1,corner | YES | 6.6 | |
| 15x15x10 | 15x15 | 10 | 2 corners | YES | 13.1 |
A cosmic-ray "beam" is defined by two plastic scintillators (T1 and T2) each 3x3 cm2. A third bigger (20x15 cm2) scintillator (T3) is used in dE/dx mode in order to reject multiple tracks. The box containing the aerogel (fig. 2-5) is positioned between the T1 and T2 scintillators while T3 is positioned below T2. An extra Cerenkov threshold counter filled with aerogel of index of refraction n=1.05 has been used to make a b selection. It appeared that the number of photoelectrons when no beta selection is applied to the cosmic tracks crossing the setup has to be multiplied by 1.14. The signal from the R5900 U PMT facing the aerogel box (n=1.03), as well as the signals from the triggering system (T1, T2, and T3) and the second aerogel counter are digitized using a Camac LeCroy ADC read by an IBM PC.