to reduce loss of helium , a pressure vessel is lined with a membrane made of tantalum.the concentrate of helium at the inner surface of the membrane is held constant at 4.44*10^-5kg/cm3, which the concentrate at the outer surface of the membrane is held constant at concentrate .the area of membrane is 2.22 m2,and the diffusivity of helium in tantalum is Dhelium=3.091*10^-11m2/s
what must be minimum membrane thickness that ensure that at steady state the helium at leak rate not exceed 1.11*10-6 kg/h?