back to article What are we more likely to see? A smooth Windows 10 May release... or a xenon-124 decay? Oh dear, bad news, IT folks

The hunt for dark matter has been fruitless so far, but scientists searching for the elusive particle have discovered another rarity: the radioactive decay of xenon-124. Xenon is a pretty unremarkable element. It's an invisible, colorless, odorless, tasteless noble gas that doesn't react much with other chemicals. One of its …

  1. JassMan Silver badge

    Interesting story, but...

    given my schoolboy maths, shouldn't there be 1.6 x 10^2 decays per year from their sample size? That is almost 1 every 2 days. If dark matter interactions are as rare as they think won't they be drowned in the noise? Or did they forget to tell us that the interactions will exhibit some completely different phenonemon from that detectected by their tank?

    1. Anonymous Coward
      Anonymous Coward

      Re: Interesting story, but...

      Maybe not "completely different", but different enough they can tell. Basically they have a known set of "things we know could/should happen based on standard physics" so they look for exceptions. If they find an exception and can't come up with a reasonable explanation under their current understanding, then it becomes a dark matter candidate and they start work trying to explain it / fit it into candidate dark matter theories.

    2. Anonymous Coward
      Anonymous Coward

      Re: Interesting story, but...

      I get about 470 decays per year, or 1.3 decays per day:

      3500kg * 1000 g/kg * 0.1e-2 Xe-124 abundance * (1/124) mol/g * 6e23 atoms/mol * (0.5/1.8e22) decays/atom/year = 470

      From the decay rate plot shown at, you can see that the corresponding peak at 64 keV just barely pops up above the background; they've been lucky it wasn't masked by the nearby contaminant peaks, which are orders of magnitude more intense.

      Hunting for the dark matter is definitly harder than looking for a black cat in a dark room - at least with the cat you know it's there, and have a decent idea what shape it is.

      1. Terje

        Re: Interesting story, but...

        You also have to factor in that only about 0.1% of Xenon atoms are Xenon 124.

        1. MJB7

          Re: Interesting story, but...

          That'll be the "1e-2 Xe-124 abundance" term

          1. Terje

            Re: Interesting story, but...

            Right, I'm apparently more visually impaired then usual and it's not even beer o'clock yet...

            1. Terje

              Re: Interesting story, but...

              Looking at the experiment homepage it seems like the mass of the detector is 3500kg, while the mass of Xenon is 62kg.

              1. JassMan Silver badge

                Re: Interesting story, but... @Terje

                You must have read a different part of the Xenon1T website description. The part I read states that there is 3.5T of Xenon with a fidudicial volume of 2T. It took a bit of extra research but I found that the fiducial volume (in the context of detectors) is the active volume which is "looked at" by the detectors. The detector system is actually a double walled cryogenic chamber with 2 tons inside the inner chamber and a further 1.5 tons between the inner and outer walls.

                What makes the whole thing look like it might be a massive white elephant is that the 2T of detection volume is actually less than 0.8m3 ie less than 1*10^15 of the volume of the earth.

                In fact the astroboffins say that this dark matter (if it exists at all,) is interstellar so there is probably not much of it within the solar system. Presumably since the whole reason for the proposition of dark matter is that it provides the missing gravity required to hold spinning galaxies together, any inside the solar system will have fallen into the sun long ago.

                Personally, I think infinitesimal is an exaggeration of the chance that a particle falling though the volume enclosed by 1AU of space on its way to the sun will actually hit an atom of xenon in a chamber the size of a small hot water cyclinder.

                1. Crypto Monad

                  Re: Interesting story, but... @Terje

                  What I'd like to know is - how do they already know the half life of Xe124, if its decay has never been observed? Is it a theoretical value? What's the level of uncertainty?

                  Direct observations which either confirm or disprove the previously expected value are equally interesting.

                2. Tomato42

                  Re: Interesting story, but... @Terje

                  while the dark matter indeed will be attracted to the sun and will fall towards it, what you write suggest you think that the sun will actually keep it there, but of of the properties of dark matter is that it is weakly interacting, sun will not stop it, it will just pass through it and continue orbiting the galaxy

                3. Anonymous Coward
                  Anonymous Coward

                  Re: Interesting story, but... @Terje

                  A T is a Tesla, a unit of magnetic field strength. At one point you refer to a volume of 2T. I can't find a reference to it on their website. Can you clarify what you mean?

                  1. Gordon 10 Silver badge

                    Re: Interesting story, but... @Terje

                    SI units nazi alert. From his context its 2000Kg = 2 Metric Tonnes = 2T

    3. Katyanna Quach

      Re: Interesting story, but...

      Yes - a xenon-124 atom does decay every couple of days or so. But it's not trivial to detect.

      I was told that the detector can measure radiation events once every second. There are 112,320 seconds in ~1.3 days, so Xenon-1T has to detect that 1 xenon-124 decay event from all the 112,320 events every 1.3 days.

      The detector has to be very sensitive and the researchers need to work out what background events to abandon to find that elusive xenon-124 decay. The Xenon experiment has been upgraded multiple times to make it more sensitive since it was first installed in 2006, so that explains why it's taken them so long to finally detect the decay.

  2. revenant

    “the rarest thing ever recorded.”

    What? Even rarer than a genuine apology for Corporate misdeeds? I doubt it.

    1. Anonymous Coward
      Anonymous Coward

      Re: “the rarest thing ever recorded.”

      Of course, when the Independent posted on FB that scientists had observed the rarest event ever, the comments didn't disappoint:

      Nigel Farage attending a Fisheries Meeting

      Liverpool/Tottenham etc. winning the league

      A blowjob *after* marriage

      A BMW driver using their indicators (US="turn signal")

      Someone admitting to liking Mrs Brown's Boys

      My brother buying a round

      An Independent story not posted as "BREAKING"

      A shopping trolley that goes in a straight line

      A Great Northern Train arriving on time

      Chris Grayling getting something right

      ... etc

      1. Aresen

        Re: “the rarest thing ever recorded.”

        All reports of BMW drivers signalling a turn or lane change are apocryphal and not from credible sources. No one has been able to duplicate the experiment.

        1. Unicornpiss

          Re: “the rarest thing ever recorded.”

          I had a BMW driver as a passenger once. I put on my signal to turn left and he said "What's that funny clicking sound?"

      2. Evil Auditor

        Re: “the rarest thing ever recorded.”

        Or a genius in a genius bar.

        The shopping trolley problem, by the way, has been solved: adding a fifth, fixed, forwardfacing wheel in the centre of the trolley.

      3. dnicholas

        Re: “the rarest thing ever recorded.”

        > A blowjob *after* marriage

        This isn't *that* rare, I can attest to that. It's not economically sustainable though, the health implications of that much prosecco notwithstanding

    2. IceC0ld

      Re: “the rarest thing ever recorded.”

      It's the longest, slowest process that has ever been directly observed .............

      and will remain so until the elusive fully functioning from the get go MS Windows update release arrives :o)

    3. Graham Dawson Silver badge

      Re: “the rarest thing ever recorded.”

      It does say the rarest thing ever recorded. If something hasn't been recorded, then it can't be compared.

    4. Anonymous Coward
      Anonymous Coward

      Re: “the rarest thing ever recorded.”

      An X-Factor winner with actual talent?

  3. SNAFUology
    Paris Hilton

    The Xenon-verse

    Does that imply/mean the universe is bigger and older than we thought ?

    1. ABehrens

      Re: The Xenon-verse

      You meant "odder than we thought".

    2. Anonymous Coward
      Anonymous Coward

      Re: The Xenon-verse

      It means you neither read not thought on the article correctly.

  4. This post has been deleted by a moderator

  5. Anonymous Coward
    Anonymous Coward


    At the current rate of progress, the most unlikely event in the universe has to be Brexit.

  6. anthonyhegedus Silver badge

    Can we make an improbability drive using a bucket of xenon then?

    1. Michael H.F. Wilkinson

      I doubt it would supply enough Brownian motion compared to a nice hot cup of tea, and the latter will only produce finite improbability.

      I'll get me coat

  7. yoganmahew

    Nothing is rare...

    at scale.

    Whether it's installations or message rates, scale will find every bug imaginable and a whole lot more you unknown unknown'd.

  8. Blockchain commentard

    I was hoping this would be about a 124 core Xenon processor. Oh well, there's always next year.

  9. Alister

    It’s an invisible, colorless, odorless, tasteless noble gas

    How do they know?

    1. Black Betty

      Because there's always a You-Tube of someone doing it.

      Cody's Lab - Breath All The Noble Gases

    2. T. F. M. Reader Silver badge

      @alister: How do hey know?

      I think it more or less a direct consequence of a gas being noble (a.k.a. inert) - no chemical reactions (at least under normal conditions), etc.

  10. SVV

    What are we more likely to see?

    As the detector is sealed 1.5 km under a mountain, we are unlikely to see a Xenon-124 release. Windows decay however is frequent and easy to observe.

    1. FozzyBear

      Windows Decay/failure

      Electron Transition Frequencies used in Atomic Clocks have trouble keeping up with the frequency of those events (

  11. earl grey

    well done, boffins

    I never cease to be amazed.

  12. adam 40 Silver badge
    Paris Hilton

    How do the electrons get into the nucleus

    Do they tunnel in? Or is it because of the wave function of the electron (or - a bit of both...)?

  13. Crisp

    I'm just imagining a legion of roman soldiers charging into the detector...

    "Did you find the dark matter?"

    "We found this atom of tellurium."

  14. Anonymous South African Coward Silver badge

    So does this mean that all Win-10-nic users are doomed to an eternity of borked updates then?

    I'll get me coat full of Linux Mint USB sticks. Yummy.

  15. iGNgnorr


    Once they've contaminated their pure xenon with tellurium, how do they remove the tellurium atom? Sounds like a particularly hard fishing expedition to me.

    1. Anonymous Coward
      Anonymous Coward

      Re: Fishing

      Density of tellurium is 6.24. Tellurium atoms will simply sink to the bottom.

      Waiting for the layer to become visible, however, will take longer than the current age of the universe.

      1. FozzyBear

        Re: Fishing

        will take longer than the current age of the universe.

        Seems like a tick of the clock compared to work laptop applying the latest updates. F*&k it, coffee time, again

      2. Anonymous Coward
        Anonymous Coward

        Tellurium solution in Xenon

        Liquid xenon is a quite decent solvent (See e.g. The chances are that it will be easily able to dissolve the tellurium produced over the lifetime of the apparatus.

        If we very generously assume that the experiment will run for 1000 years, then the decay of Xe-124 will produce about 1e6 tellurium atoms over this time, giving the molar concentration of about 1e3 atoms/litre (rounding the liquid xenon density to 3.5 g/cm3), or on the order of 1 zeptomole/litre (1e-21 mole/litre). If we assume that the xenon is kept just above its freezing temperature at the ambient pressure (ie 162K), this concentration of tellurium will remain dissolved as long as the Gibbs free energy of dissolution at this temperature is less than:

        -R T ln [Te] = -8.3 J/mol-K * 162 K * ln(1e-21) * 1e-3 kJ/J = 65 kJ/mol

        In chemical terms, this is an enormous number - it exceed the heat of vaporization of Tellurium (which is about 53 kJ/mol). I can't be bothered to estimate the free energy of vaporization at 162K, but it will be less than 53 kJ/mol, since vaporization increases the entropy. So, the tellurium will definitely remain in solution after 1000 years.

        How long will we have to wait to see it to start precipitating at the bottom? Let's take 53 kJ/mol as the worst-possible-case estimate of the free energy of dissolution. Then, the critical concentration of tellurium will be:

        exp[-53 kJ/mol * 1000 J/kJ / ( 8.3 J/mol-K * 162 K )], which is about 10 atto-mole/litre (1e-17 mole/litre)

        That's the concentration we'll reach after waiting for 10 million years. Because the actual free energy of tellurium dissolution is xenon is very, very unlikely to be this high (after all, Xenon -is- a good solvent), we'll probably have to wait for much longer. Each 10 kJ/mol decrease in the free energy will increase the waiting time by a factor of 1700 at this temperature - so it won't take much to get us beyond the lifetime of the universe so far.

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