Producing x-rays: technical details
This section is now split up into two parts.
This part focuses on rectifier tubes (e.g. DY802), which I tried first. Rectifier tubes are cheap and relatively easily available, but have disadvantages: They are not designed for high power dissipation, and most don't take very high voltages. Rectifier tubes are operated in cold cathode mode with fixed operating voltage.
The PD500 tube is a "beam triode" used in old TV's to regulate the acceleration voltage for the CRT. As such, it is specified for 25kV and 30W max. anode dissipation. Good tubes take up to 70kV without cold cathode discharge. This makes it possible to choose acceleration voltage (penetration power) and anode current (intensity of x-rays) indepently. Also, output intensity is much higher than with rectifiers. One disadvantage is that radiation is produced inside the anode cylinder and has to pass it to get out.
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