Can one see radioactive substances with an X-ray detector? I was wondering the other day an X-ray detector (like the ones used at airports) can detect gamma-rays lets say from a sample of uranium. I know its all electro-magnetic waves but I'm really unsure about how it works in practical terms.
Edit
Now out of curiousity, if you got an beta-radiator, might that go unnoticed?
 A: In wikipedia there is an extensive article about x-ray detectors and one on gamma ray detectors.
Detectors are calibrated to work with specific frequencies and though there will be some effect  from a gamma ray source on an x ray detector, and vice versa, to make sense of it one would need the proper calibration. 
Now if you are asking whether when luggage is radiated by x rays and a "picture" taken if gamma radiation will show up, it is  improbable mainly due to the distances involved: radiation from a source falls as 1/r^2 and is incoherent, whereas the xray detector uses coherent/and or parallel x-rays. It would need a very large source to show up on the picture.
They must have special Geiger counter detectors to catch illegal radioactive material being passed.
A: Short answer to the title question: yes. 
They are both species of ionizing photons, and you use the same set of mechanism to detect either band. Typically hodoscopes (perhaps based on fiber and high gain photo-diodes), multi-channel plates, or silicon strip detectors.
That said, I suspect that anna is right when she says that the machines used to scan luggage at the airport are not designed, or tuned to detect low levels of radioactivity (say kBq) in the baggage. The geometry that is most favorable for fast planar scanning will not be good at imaging a point source, and the designed flux is probably pretty high, meaning that weak sources only tweak the results by a little bit.
I have seen colloquia from people involved in designing large scale scanning machines for (shipping containers), and they but a great deal of thought and effort into the matter. Hand luggage is surely easier, but still non-trivial.
A: Radioactive substances (radioisotopes) are generally available as salts or metals. In the form of salt, they are in micro gram quantities, so the salt cannot be seen by naked eye.However, ionizing radiations particularly the gamma rays or beta particles can be detected by appropriate scintillation detector. Cobalt -60 source is available in salt form and in metallic form. The source in metallic form called pellet can be seen with naked eyes. 
