Applications of Transmission Electron Microscopy
application
Due to the high gain and short response time of the photomultiplier tube, and because its output current is proportional to the number of incident photons, it is widely used in astrophotometry and astrospectrophotometry. Its advantages are: high measurement accuracy, can measure relatively faint celestial bodies, and can also measure rapid changes in celestial body luminosity. In astronomical photometry, the multiplier tube of antimony cesium photocathode is widely used, such as RCA1p21. The maximum quantum efficiency of this photomultiplier tube is around 4200 Angstroms, which is about 20%. There is also a photomultiplier tube with a double alkali photocathode, such as GDB-53. Its signal-to-noise ratio is an order of magnitude larger than that of RCA1p21, and its undercurrent is very low. In order to observe the near-infrared region, photomultiplier tubes with multi-alkali photocathode and gallium arsenide cathode are commonly used, and the quantum efficiency of the latter can reach up to 50%.
Ordinary photomultiplier tubes can only measure one piece of information at a time, that is, the number of channels is 1. matrix. Since the number of channels is limited by the thin metal wire at the end of the anode, only hundreds of channels can be achieved.
operating characteristics
1. Stability
The stability of the photomultiplier tube is determined by many factors such as the characteristics of the device itself, working status and environmental conditions. There are many situations where the output of the tube is unstable during the working process, mainly including:
a. Jumping instability caused by poor welding of electrodes in the tube, loose structure, poor contact of cathode shrapnel, tip discharge between electrodes, flashover, etc., and the signal is suddenly large and small.
b. Continuity and fatigue instability caused by too much anode output current.
c. Effect of Environmental Conditions on Stability. As the ambient temperature rises, the sensitivity of the tube decreases.
d. Humid environment causes leakage between pins, causing dark current to increase and become unstable.
e. Environmental electromagnetic field interference causes unstable work.
2. Limit working voltage
The ultimate working voltage refers to the upper limit of the voltage that the tube is allowed to apply. Above this voltage, the tube will discharge or even break down.
