fotomultipliäriä

A fotomultipliäri, or photomultiplier tube (PMT), is a highly sensitive detector of light. It is capable of detecting single photons. A PMT consists of a vacuum tube containing a photocathode, a series of dynodes, and an anode. When light strikes the photocathode, it emits electrons through the photoelectric effect. These electrons are then accelerated and strike the first dynode, releasing more electrons. This process is repeated through a cascade of dynodes, with each stage producing a larger number of electrons. Finally, the amplified electron signal is collected by the anode, producing an electrical pulse that can be measured. The gain of a PMT, which is the ratio of the number of output electrons to the number of input electrons, can be very high, on the order of 10^6 or more. This high gain makes PMTs ideal for detecting very faint light sources. They are commonly used in scientific instruments for applications such as spectroscopy, particle physics experiments, medical imaging, and astronomy. The sensitivity of a photomultiplier tube is dependent on the wavelength of the incident light, with different photocathode materials exhibiting varying spectral responses.