Designing a New Apparatus for Measuring Particle Sizes of Nanometer Order by Light-scattering (4th Report)

Formulation for Output Characteristics of Photomultiplier and Improvement of Dynamic Range

Abstract

A new method has been developed to measure particle sizes of nanometer order on raw Si wafers by using a photomultiplier (PMT). The dynamic-range of a PMT used to detect extremely weak light is narrow generally. And moreover, as its rated current has a very low value, a protective circuit needs to guard the PMT against over-current due to unexpected very large particles. In this study, it was tried to derive theoretical formula for calculating the output current on the PMT quantitatively. By estimating the characteristics of the output current by the obtained formula, a method for protecting the PMT by using the saturation region at the characteristic of output current can be devised. As a result, it can be verified that this method could simplify the measuring method and the instruments, and it could magnify the dynamic range of the PMT in measuring extremely weak lights.