A typical FIREX target is assembled with a 500 μm diameter PS shell, a glass fill tube and a gold cone guide. Each part is glued together by an epoxy resin. To date, several assembled targets have been cooled down to cryogenic environment. However, they could not survive a cool down process and appeared to rupture around the glued boundary between the PS shell and cone guide. To reveal a crucial factor of the target destruction, its thermal stress after cool down was calculated using the ANSYS code. A two dimensional axisymmetric calculation model is composed of the PS shell and cone guide glued by an epoxy resin which is covered on by an epoxy fillet. A cool down process from 293 K to 10 K was simulated. The calculation showed that the rupture of the shell would start from the PS shell and gold cone guide boundary and the target validity depended on how the epoxy fillet could reinforce the PS shell.
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