Patent ID: 7257990

Claim:
A method for measuring ultralow moisture permeation through a sample at a temperature substantially above ambient using a radioactive compound, which method comprises the steps of: heating the sample being measured to a desired test temperature substantially above ambient, providing a first controlled access region adjacent an upstream surface of the sample, providing a second controlled access region adjacent to a downstream surface of the sample, supplying a defined amount of radioactive gas sufficient only for a single test to the first region at predetermined relative humidity at said test temperature so as to be in contact with the upstream surface of the sample, said radioactive gas being provided in a sealed glass ampoule and supplied by fracturing said glass, collecting radioactive gas permeating from the downstream surface of the sample by circulating a very slow flow of dry carrier gas through the second region to provide a radioactive stream, flowing said radioactive stream from said second region to an ionization chamber containing a beta-particle radiation monitor, continuously monitoring said stream in said ionization chamber to detect the presence of beta-particles emitted by the amount of said radioactive gas which permeates through the sample and generating signals reflective thereof, and receiving said signals from said radiation monitor and converting the signals to calculate the permeation rate through the sample, whereby the sensitivity of the method allows for measurement of permeation of moisture at a rate of 0.001 gm or less/m 2 /day, and continuing such operation at said test temperature over a period of at least about 2 days to attain a substantially steady state of moisture permeation for the sample, whereby the barrier performance of the sample for at least one month can be assessed from said steady state measurement.