The purpose of the calorimeter is to detect the scattered photons and measure their energy and the position at the calorimeter face. These values, along with the coordinates of the interaction point in the target, provide the photon 3-momentum.
The calorimeter consists of 704 modules of TF1 lead glass, of 4×4×40cm2 size, arranged in a matrix of 22(X)×32(Y) columns and rows.
The properties of TF1 lead glass are summarized in a table elsewhere. With the given module size of 4×4×40cm2 and the type of PM used one obtains on average about 1100 photo-electrons per energy deposit of 1 GeV.
The length of the module makes 14.6 RL. The length sufficient to absorb 98% of a shower was estimated for TF1 in a paper from GAMS as l0.98=30+4·lnE (cm). A 40 cm module absorbs more than 98% of showers at E<12 GeV.
Radiation hardness of TF1 was studied in a paper from GAMS by irradiating the glass blocks by pions and protons and measuring the attenuation of the response for electromagnetic showers and other light sources. They obtained that the response drops by e times after the block of about the same size as ours absorbs about 5·1010 negative pions. One can roughly estimate the corresponding dose. The hadron shower leaves about 2 GeV of energy deposit on average, concentrated in the second half of the module, closer to the PM tube. Estimating the effective weight of the material involved as 1 kg one obtains a dose of about 2 krad.
We measured the radiation damage of the TF1 glass modules in Hall A:
The sizes of every block have been measured. The results are:
The lead glass blocks will be viewed by the venetian blind 12-stage USSR-made FEU 84-3. The following information is available: