Tell me more ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.
up vote 3 down vote favorite

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?

share|improve this question
The issue with betas is going to be range. The machines presumably work in air rather than vacuum, so the distance beta travel before ranging out is relatively short. In most of the designs I envision they range out before they are detected. Alphas are stopped long before they leave the luggage. – dmckee♦ Apr 30 '11 at 3:53

2 Answers

up vote 1 down vote accepted

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.

share|improve this answer
surely no one should make such claims without evidence.. – qftme Apr 30 '11 at 3:00
@qftme: The basis of the claim is that x-rays and gamma-rays are both photons with sufficient energy to ionize matter, and that's how we detect them. I would point a student at Leo or something similar, but it follows from the basics of high energy photons interacting with matter (PDF link!). – dmckee♦ Apr 30 '11 at 3:11
up vote 3 down vote

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 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.

share|improve this answer
Thanks a lot, I think I understood it now, i forgot about 1/r^2 – Sebastian Godelet Apr 29 '11 at 15:39
+1 for the logical experimentalist perspective – qftme Apr 30 '11 at 3:04

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.