I'm trying to create a setup where I would have xrays emitted through a photodiode (the non sensitive side). I do not want the photodiode to detect these xrays going through it, only the xrays which return back to the source.

My question is then, are photodiodes sensitive to light going through the opposite side, through the back of it? (Going through from behind it)


  • \$\begingroup\$ No if the case bottom is metal \$\endgroup\$ – Tony Stewart EE75 Jan 4 at 14:51
  • \$\begingroup\$ Even if the answer is no (they are not sensitive to light from behind) they may be sensitive to X Rays. \$\endgroup\$ – user_1818839 Jan 4 at 17:35
  • \$\begingroup\$ The term x-ray (NASA def) means anything from \$120\:\text{eV}\$ to \$50\:\text{keV}\$, though other definitions also exist, but which either way is quite a span with quite a range of possible interactions. I don't see how anyone could possibly give you a bright-line answer with so little information provided. Please start by discussing your source. Also, please discuss your photodiode and its physical arrangement to the source as best you can. I'll assume you are not using scintillation unless you say otherwise. \$\endgroup\$ – jonk Jan 4 at 21:01
  • \$\begingroup\$ I have used, accidentally at first, Hamamatsu photodiodes for x-ray detection and measurement. It took me just a moment looking at the data I was gathering to realize that the unexplained events in the data were most likely due to x-rays or cosmic rays. It took me a week of research to work out the expected level of events in my photodiode at my altitude and location on Earth and to find it consistent with the recorded events in collected data measured in the photodiode. Orientation of the photodiode greatly influenced the collected electrons per event as well as mean frequency. \$\endgroup\$ – jonk Jan 4 at 21:05

Assuming the photons can get though the metal and wiring, they can be equally absorbed from the front or back. This is why both front illuminated (photon approaches from the metal side) and back illuminated (photon approaches from the junction side) image sensors are used.


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