Total Absorption Counter
From GlueXWiki
CLAS Total absorption counter used for PrimEx
The table below summarizes the information I obtained from various sources about the TAC counter that GlueX borrowed from CLAS.
| Property (source) | Value |
|---|---|
| Material (from Mahbub) | SF-5 Lead Glass |
| Composition by weigth (Web) | 55% PbO, 38% SiO2, 5% K2O, 1% Na2O |
| Length (from Mahbub) | 40cm |
| Height (from Mahbub) | 20cm |
| Width (from Mahbub) | 20cm |
| Weight of lead-glass block | 65 kg |
| Density (Web) | 4.08 g/cm^3 |
| Radiation Length of material (Web) | ~25mm |
| Critical Energy (Web) | 15.8 MeV |
| Refractive index (Web) | 1.67270 |
| PMT (from Mahbub) | 5 inch Hamamatsu R1250 PMT |
Observed problems
After using Hall B lead glass TAC between 2016 and 2017 the light output significantly decreased. The radiation hardness of this lead glass is highly unlikely to exceed 10^5 rad. We are not going to be able to significantly reduce the radiation dose received by TAC since we need to accumulate meaningful statistics in the pair spectrometer with a reasonable converter thickness that does not distort the PS acceptance shape with respect to the production converter. Therefore, it is important for GlueX to have a total absorption counter made of material with radiation hardness of ~10^6 rad or better.
Options considered earlier
- lead-glass counter array:
- efficiency ~100%
- to avoid radiation damage: rate < 100kHz using radiator of 10-5 X0 and ~100 pA beam
- Cerenkov counter (higher current - but probably lower efficiency)
