Gamma chamber 4000A is a compact and self-contained irradiation unit of Cobalt-60, offering an irradiation volume of approximately 4000 c.c. The unit consists of the following main parts: a) source and cylindrical source cage, b) biological shield for the source, c) inner shielding plug, d) central drawer, e) mechanical drive system, f) electrical control system and g) external cabinet. Gamma irradiation unit holds up to several thousand curies of Cobalt-60 and it have been developed at Bhabha Atomic Centre (Bombay, India) for radiation research in different fields.