| 摘要 |
<p>Apparatus for accurate measurement of the density-thickness or mass per unit area of a material placed between a radioactive source and an ionization chamber, in which the apparatus is calibrated by using a plurality of standards of known mass per unit area or basis weight to provide a relationship between basis weight and the output current of the chamber which includes at least terms of the second order and preferably includes terms of the third and higher orders. The accuracy is increased by enclosing the major portion of the radiation path in airtight chambers, leaving only enough of the path exposed to the external atmosphere as is necessary to provide a working air gap through which the material may pass. The airtight chambers are of sufficiently rigid construction that the density of the gas therein is substantially constant and independent of ambient temperature and pressure variations. The accuracy is further increased by measuring ambient temperatures and pressure fluctuations, and linearly compensating the computed basis weight for resultant density variations in the small working air gap.</p> |
