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Are there special muller tubes that only measure alpha for example?

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    $\begingroup$ Why do you think it is not possible? Yes, there are special alpha particles detectors. Google query="selectively detecting alpha particles" $\endgroup$ – Asphir Dom Aug 25 '13 at 14:04
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Most particle detectors work by detecting the ionization caused by the particle or the secondary effects of that ionization like scintillation light (the exceptions work on Cerenkov light and transition radiation), so it is difficult to say "only detect ionization from alphas".

However, the physics of ionization and the geometry of the deposition depend on the mass, charge and energy of the particle doing the ionization, which gives us many ways to identify the particle involved. Ionization density and profile along tracks, track length compared to calorimetry, pulse shape discrimination in scintillators, combining calorimetry with velocity or momentum determination and so on.

Perhaps the easiest way with moderate energy alphas would be to use a segmented surface detector of some kind, vetoed by a deeper detector with similar segmentation (relying on the fact that alphas range out much faster than gammas or betas). This would not help you to discriminate against heavy fragments, but would be otherwise very reliable.

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  • $\begingroup$ As a special case, if you're just holding a source in your hand and you want to find out what it's emitting, you don't need a special detector -- you can just vary the distance to the detector and see whether there is a complete cutoff due to absorption of alphas in a certain amount of air. $\endgroup$ – user4552 Aug 25 '13 at 22:08
  • $\begingroup$ @BenCrowell When we did the ranging out of alphas in lab in grad school we did it in a bell jar, and needed rather less than a full atmosphere to range some out in 3 cm. Can't recall the isotope off-hand but I assume they were circa 4 MeV. $\endgroup$ – dmckee --- ex-moderator kitten Aug 25 '13 at 23:53

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