Balloon borne CALET Prototype Payload (bCALET) for Electron and Gamma-ray Observation

We are planning a balloon observation of cosmic-ray electrons, γ-rays and heavy nuclei, using the CALET prototype detector, named bCALET- 2. bCALET-2 is 1/12 scale model of the CALET detector. It is composed Imaging Calorimeter(IMC), Total Absorption Calorimeter(TASC) and Silicon pixcel Array(SIA). IMC has an area of 256mm×256mm, and is consisted 8 x-y layers of scintillating fiber belts inserted below tungsten plates (3.57 r.l. in total) for a fine imaging of shower particles. TASC is made 6 layers of BGO scintillator logs (25mm×25mm×300mm in each) with an area of 250mm×250mm, for measuring the total energy deposit of incoming shower particles. The geometrical factor, SΩ, is nearly 300cm2sr. A part of detector is covered at the top by SIA for distinction of the charge of primary heavy particles. We will observe 1 - 100GeV electron and a few 10MeV - 10GeV γ-ray to study the feasibility of CALET. The balloon flight is scheduled in Sep. 2009 at Taiki Aerospace Research Field, Hokkaido, Japan. In this paper, we will report the R&D study of the bCALET-2 detector and a future plan for bCALET-3 and CALET.