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In American-British drama miniseries Chernobyl, on the second episode, a scientist takes some dust from the outer surface of a window and places it in an instrument that tells her what radioactive isotope was in the sample.

She places the sample in the device in the middle and then fiddles with the electronics. The device on the right seems to include some form of oscilloscope. She then tells the colleague, upon handing him the printout,

"Iodine 131. It's not military, it's uranium decay, U-235."

"Reactor fuel?"


What was the instrument that was used? And how was the scientist able to deduce that there was a nuclear explosion?

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    $\begingroup$ That sounds way too convenient... $\endgroup$
    – user137661
    May 16 '19 at 21:50
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    $\begingroup$ We could perhaps say with great confidence that it was some form of spectrometer, but they come in two varieties: mass spectrometers try to figure out how big the atoms in a sample are, the normal kind just gets a spectrum from whatever radiation it already sees and in this case you would be looking for a gamma-spectrometer or an alpha-particle spectrometer. Of those I would imagine the older and more proven tech is the mass spectrometer, but I am absolutely unsure about this TV series or what historical events the scene was attempting to mimic. $\endgroup$
    – CR Drost
    May 16 '19 at 22:01
  • $\begingroup$ at 3.21 here $\endgroup$
    – user_1_1_1
    May 16 '19 at 22:53
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Exactly was is depicted in the miniseries is difficult to answer without a clip, but there are a few different devices that can achieve something similar.

A mass spectrometer can be used to measure the mass of an isotope. With enough accuracy and some tables, this can be enough to identify an isotope in some cases.

It could also be a gamma-ray spectrometer, which measures the energy of detected gamma rays. Since many isotopes have distinctive gamma ray energies, this can be used to identify isotopes in most cases.

There are short-lived isotopes that don't occur in nature. The detection in any significant concentration of any such isotope would indicate a nuclear accident of some kind.

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  • $\begingroup$ @Chris See information added to the question -- there isn't much else that you'd get from watching a clip. From general-physicist eye, there is a heavy implication that the device is a gamma-ray spectrometer (or maybe something measuring betas or alphas) rather than a mass spectrometer. Not that the show holds itself to such an extreme level of accuracy that they couldn't have compressed this episode to something plausible but shorter than what it'd take in the real world. The character in question, Ulana Khomyuk, is, after all, a composite character. $\endgroup$ Jun 8 '19 at 18:38

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