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What causes those radiation readings in my radiation meter (See the linked video)? Metal pieces were magnetized.

Used radiation detector is RADEX RD1503. "Radiation" is not generated if the tube has been wrapped inside an aluminium foil. Should induction occur through thin aluminium foil? At least magnet holds through that foil and plastic tube.

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Is there the possibility that radiation meter is encountering induced current from the magnetic field of the metal pieces? Unless I'm mistaken, this could be possible if it is reading the induced current as ionizing events. –  WM_Undergrad Jun 25 '14 at 13:43
@WM_Undergrad Edited –  Kimmo Rouvari Jun 25 '14 at 16:12
There is much that is unclear here. "Radiation meter" is deeply unhelpful--what type of detector do you have? Is it a Geiger-Müller tube? A chip of scintillator with a PMT on it (a solid-state photon detector)? I don't imagine it is a germanium detector but it could be a silicon detector. All these instruments have different properties. And asking us to go look at a video without the courtesy of even describing what might be at the other end is a big turn off for me. I never follow a link in a question unless you've done the work to convince me it is worth my time. –  dmckee Jun 26 '14 at 1:32
BTW--the answer to my question is in your link--but again you are asking us to do work that is your responsibility as the asker; it's a Geiger counter which means that @WM_Undergrad's suggestion is imminently reasonable. (but unproved without some details about how the signal behaves). There is a simple test, but I'll let WM_Undergrad suggest it. –  dmckee Jun 26 '14 at 1:35
@WM_Undergrad A note on foil "Faraday cages": if the foil is smooth it just re-radiate the signal (at least for wavelengths comparable to or smaller than the size of the object you are shielding) and only cut it by about a factor a two. This is a case where neat work is counter-indicated. Crinkle it up before putting it on and it'll work much better. When you understand why you'll know a useful little thing about E&M. I verified this fact experimentally while I was a grad student as I needed (and eventually got) about a factor of ten noise reduction in a high speed circuit near a flash lamp. –  dmckee Jun 26 '14 at 2:17

2 Answers 2

up vote 1 down vote accepted

As we're discussing above, it seems that the detector you're using seems to be functioning properly when used with verifiable radioactive material. The extra clicks are being caused by current induced in the counter by magnetic flux when you may be moving the detector. In order to get around this, it seems that you should use, in addition to the crinkled foil suggested by dmckee, a setup that involves keeping the business end of the detector and the sample under test stationary, thereby removing the current being induced by the changing magnetic field. Many thanks to dmckee for the insights above.

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I'm puzzled by the fact that aluminium foil (crinkled or not) blocks those increased meter's readings. Also, I can't increase those readings with my Neodymium magnets no matter what. Naturally, in that stationary case nothing happens. –  Kimmo Rouvari Jun 28 '14 at 3:34
The aluminum foil counteracts magnetic flux (changing magnetic field). When the foil encounters a changing magnetic field, the flux induces eddy currents in the foil. These eddy currents generate a magnetic field to counteract the flux, thereby removing the changing magnetic field from your radiation meter. As a result, a stronger magnetic field causes larger eddy currents and thusly a still net 0 magnetic flux, thereby blocking the false induced readings. –  WM_Undergrad Jun 28 '14 at 18:46
Do those eddy currents generate their own magnetic field which should affect the meter? Maybe I should repeat my experiment in the future with various new twists in it. –  Kimmo Rouvari Jun 29 '14 at 3:04
No, these eddy currents generate their own magnetic field which resists change in the overall magnetic field, therefore they reduce the effect on the meter. Thus, with the foil, your measurements are more accurate. –  WM_Undergrad Jun 29 '14 at 3:06
Thanks! Now I got it. Anyway, I have to make new experiments in future on the subject, more fine tuned and sophisticated. This conversation inspired me a lot. –  Kimmo Rouvari Jun 29 '14 at 3:40

It's very unlikely, but not impossible, that the metal stock your magnets were made from was contaminated with a radioactive isotope. I mention this because I once encountered radioactive re-bar - it was only noticed because it was brought into a lab with radiation detectors at the door. Eventually it was traced back to contamination (radioactive cobalt) and a complex (and falsified) supply chain to the manufacturer.

Try magnets of different composition, and from different manufacturers, and if only these produce the effect you might suspect something. Chemical analysis by a mass spec could also confirm whether the magnet contains a radioactive isotope.

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Hi Mark, those metal pieces were magnetised by myself and there was no radioactive contamination present. Actually, at the beginning of the video one can verify that. –  Kimmo Rouvari Jun 28 '14 at 3:22
@WaitMeDude "there was no radioactive contamination present" While you are almost certainly right for your purposes, those of us who have done low-background particle physics know just how tricky that kind of claim is. Mark's cobalt-bearing re-bar is not a qualitative anomaly, merely the high activity tail of a very broad distribution. Something on order of 1/3 or 1/4 of the ambient ionizing dose comes from the extant radioisotopes that surround us day in and day out. –  dmckee Jun 29 '14 at 15:28

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