ISAI is an experiment of solar axion search dedicated for axion-nucleus interaction.
An event-triggered monolithic Silicon On Insulator (SOI) X-ray pixel detector cooperated with position sensitive anti-coincidence timing counter observes a 14.4 keV gamma-ray as a converted signal of solar axion by Fe-57 isotope.
Because the background from radioactivity in detector defines the axion sensitivity,
we had developed a rigid-flexible circuit board to separate the pixel sensor and the peripheral electrical components having major radioactivities.
Two timing triggers from the pixel detector and the anti-coincidence counter are recorded by a high time resolution DAQ system so that background induced by cosmic-ray or environmental radiation can be rejected in the offline analysis.
We will present the experimental apparatus, the commissioning and the first background observation using the half detector without the anti-coincidence measurement.