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Deadly detection question

  1. Mar 26, 2014 #1
    Hi everyone,
    As you might gather from my moniker, I am a writer. I'm working on a sort of crime novel and have a weird question for you. I have a character who wants to kill another character using a particle detector. I have a couple ideas already but need one using a solid-state semiconductor detector, which obviously is difficult with the detector alone. Thus I'm thinking about the dilution refrigerator.

    Could one have one of those just sort sitting in one's lab (with, I presume, the detectors inside it), and would it get tremendously cold on the outside--so cold, in fact, that you could press someone against it and freeze them (or their skin, anyway)?

    Other ideas welcome as well....

    Thanks!
    Writermon
     
  2. jcsd
  3. Mar 27, 2014 #2

    Bandersnatch

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    I used to work in a factory making those. We always had at least one standing around being tested. They're perfectly safe, and as such I assume they are indeed placed in labs.

    No sort of cryogenic device(cryostat) would ever get cold on the outside, unless damaged.

    Cryostats are vacuum-insulated flasks(dewars), usually with two-stage insulation and refrigeration(one using liquid nitrogen, the other liquid helium).
    In one of common designs the sample is cooled by a liquid helium bath in a sealed container, vacuum-insulated from another container cooled with liquid nitrogen, which in turn is again vacuum-insulated from the outer walls. In the vacuum spaces additional radiation insulation(i.e., reflective aluminium foil) is installed to minimise heat transfer inwards.
    The outer walls of the dewar lose heat only via radiative transfer of energy, which is inefficient enough not to lower their temperature noticeably below room temp.

    If the dewar walls were actually cold to the touch, it would mean that a significant amount of heat is being transfered towards the sample, which is exactly what the device is supposed to prevent.


    As for other ideas, you could perhaps have a large spill of liquid nitrogen?
    1 litre of liquid nitrogen after evaporating will take up 400 litres of volume. A large enough spill could conceivably change the composition of air in a room to bring oxygen content below safe levels and cause asphyxiation in the victim.
    If you can get the oxygen content in air below 10%, the victim is as good as dead.
    You'd need a pretty large spill, preferably near a heat source, as L.nitrogen doesn't evaporate very fast when exposed to room temperatures.
    The cryostats don't hold a whole lot of cryogenic liquids in them, but both helium and nitrogen are usually supplied from a separate, large dewar, which could serve as the source of the spill.
     
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