The HERMES calorimeter is
composed by 840 radiation resistant F101
lead-glass (LG) blocks arranged in a configuration with one wall above and one below the
beam, and with photomultipliers (PMTs) viewing from the rear.
Each wall is composed of 420 identical lead-glass blocks, stacked in a 42x10 array. Each block has an area 9x9 cm2 and a length of 50 cm
(about 18 radiation lengths). This cell size meets the requirement that about 90% of the
shower is contained in the cell for an axially-incident positron.
The blocks were polished, wrapped with 50 mm thick
aluminized mylar foil and covered with a 125 mm thick
tedlar foil to provide light isolation.
Each wall is composed of 420 identical lead-glass blocks, stacked in a 42x10 array.
Each block has an area 9x9 cm2 and a length of 50 cm
(about 18 radiation lengths). This cell size meets the requirement that about 90% of the
shower is contained in the cell for an axially-incident positron.