Development of Total Absorption Calorimeter of CALET

We have been developing a total absorption calorimeter (TASC) for CALET instrument. The performance of two types' crystal scintillators, i.e. bismuth germanate (BGO) and lead tungstate (PbWO4 ), has been studied as the material of TASC. We have compared several products, BGO by Crismatec and SICAAS and PbWO4 by SICAAS and Belarus. The light yield for low energy deposit was measured by a photomultiplier tube (PMT). It was almost the same both for Crismatec's BGO (372.0 p.e./MeV) and for SICAAS's (363.6 p.e./MeV). The light yield of PbWO4 is smaller than that of BGO, as expected, by a factor of 45 on average. The read-out using a photo dio de (PD) was tested for BGO in realistic set-up. The results of PD is consistent with that of PMT, and it is confirmed that PD is capable of detecting 0.5 MIPs in BGO with thickness of 2.5 cm.