Don't cross the LHC stream!

By Phil Plait | September 21, 2010 7:05 am

There are a lot of questions in science that seem simple, but in fact lead to profound concepts. Why is the sky dark at night? Why does gravity pull me down? Why is the Sun hot?

And some questions seem silly and frivolous, but it turns out are really hard to answer, and in fact scientists might disagree on the answer. Case in point: what happens if you put your hand in the beam of the Large Hadron Collider?

So the folks at Sixty Symbols asked this of several scientists, and the first four minutes of this video are the result:

Fantastic! I love how different scientists think of different angles on this, and come up with different answers. Clearly, they hadn’t really thought about this before, so as they realize various aspects of this the answer changes.

It’s complicated! You have to think about the energy of the beam, of course, but also the energy of a given proton as it moves at 99.9999% the speed of light. But that number doesn’t mean anything if the proton doesn’t actually interact with the matter in your hand, so you have to consider the "cross-section" of the atoms in your hand. Think of it this way: if you shoot a gun at a target, you make a hole. But if you shoot a gun at a fishing net, it might pass right through. Most of the area of a fishing net is holes! The nuclei of atoms are very small compared to the atoms themselves, so in a sense most of you is empty space.

And there’s more. The beam of the LHC is in a small tube that’s a high-grade vacuum — getting your hand in there would be tough. And there’s a magnetic field of ferocious strength there, so I hope you don’t have any metal bits in you. And there are actually two beams going in opposite directions.

So taken in total, I’m not sure what would happen. If the total energy of the beams were dumped into your hand all at once, it would act like dropping a bomb on you. One of the scientists in the video says the total energy in the beams is 300 megajoules, which is equivalent to 75 kilograms (165 pounds) of TNT going off. That’s about 300 sticks of dynamite, if you’re curious.

Bang! Ow.

But depositing all that energy all at once may not be possible; protons are so small they may not all hit you and suddenly stop. That’s why I find the scientists’ answers so amusing. One says it would explode, but that’s because he assumes all the energy gets dumped into your hand. Another thinks nothing would happen, because the energy that actually interacts with you is small. Another thinks about the synchrotron energy produced, which is radiation emitted by the particles themselves as they circle the tube.

The point? The actual answer is hard to state with certainty until you look at everything involved! There are a lot of factors involved, making this seemingly easy question actually a bit of a puzzler.

So I propose that in a few decades, when funding is running low and the LHC’s primary objectives are met, we test this idea out. We don’t have to use an actual hand — logistics might be difficult — but I think a nice slab of rib eye might do the trick. But they better make sure a few interns are on hand to clean the LHC up afterward, just in case the whole 300 sticks of dynamite thing turns out to be the correct outcome.

Tip o’ the lead shielding to AstroPixie.

Related posts:

My excellent CERN adventure
Breaking: The LHC still will not destroy the Earth
Brian Cox calls ’em like he sees ’em
Cox on TED

CATEGORIZED UNDER: Cool stuff, Science, Top Post
MORE ABOUT: LHC, protons, Sixty Symbols

Comments (119)

  1. And you thought that making popcorn with lasers could be fun!

    <Homer>Mmm… Rib eye…</Homer>

  2. Nick

    Why not as Anatoli Bugorski ? Admittedly that was a Synchrotron, though.

  3. Brian Schlosser

    “Sadly, it was discovered too late that while the LHC alone could not destroy the world, the LHC plus a slab of Grade A beef would, in fact, tear apart the fabric of space-time leading to the total annihilation of the solar system”

    — Slawthos the Profound, “A (Very) Brief History of the Human Race”, University of Maximegalon Press

  4. Gus Snarp

    Um, one of those scientists has the “Atlas of Creation” on the shelf behind him. What’s up with that? Who is that guy, and can we assume he owns it because he wanted to debunk it, or did they actually find a creationist physicist to interview?

  5. Gus Snarp

    Isn’t it possible that it wouldn’t do anything you would feel, but might give you some form of cancer? Or better yet, super powers! I’m thinking it makes you into Dr. Manhattan. Yes, that’s it. It’s all just subterfuge to keep us from realizing the true purpose of the LHC – they’re going to use it to turn Stephen Hawking in to Dr. Manhattan.

  6. Frank

    “Paging Adam and Jamie to the white courtesy phone, Adam and Jamie, white courtesy phone.”

  7. Mike G
  8. Tony

    My hope would be that something in between the extremes happens, resulting in a perfectly cooked rib eye. In addition to being the most complicated machine man has ever built, CERN would also have the worlds most expensive barbecue.

  9. TCs

    “so I hope you don’t have any metal bits in you.”

    You don’t have to have any metal bits, the water in the hand is diamagnetic. According to that link, 16 T is probably enough to levitate a mouse or a frog and the LHC has about half that flux density.

  10. Michel

    As long as it goes BOOM I´m all for it!
    Maybe Adam [tm] can build a small one.
    He likes BOOM too.

  11. Bethany

    Alright, here’s what I calculated:
    The protons are high energy with lorentz factor of gamma=7500, kinetic energy is about K=7×10^6 eV. The paper cited below says that the stopping power of a proton going 10^6 eV is about 2.5×10^8 eV cm^2 g^-1. Using the density of muscular tissue rho=1g cm^3 and the thickness of my hand of 1 cm, the energy deposited is 2.5×10^8 eV. In other units its 1.07×10^-11 calories, 4.49×10^-11 Joules, and 1×10^-14 grams of TNT. If there are hundred billion protons per bunch in the beam (as the video said) then for every bunch you get 4.49 Joules or 0.001 grams of TNT of energy.

    So, what will 0.001 grams of TNT do to your hand? Anyone wanna call Mythbusters?

    Thanks Phil. That was a great problem, I think about particles, energy, cross sections and column depth all the time.

    E Waibel and G Willems 1987 Phys. Med. Biol. 32 365


    o/^ and the science gets done
    and you make a neat gun o/^

  13. Bethany

    The other question is how long will you leave your hand in the beam? What is the rate of the bunches around the beam? How long will it take for you to receive 1 ton of TNT energy? My guess is 2 minutes.

  14. CR

    (without having seen the video link) Strangely, I’m reminded of a line from an early Star Trek Next Gen episode that went something along the lines of “Careful! That’s a strong enough magnetic field to suck the iron right out of your blood!” I’m guessing that might hurt a bit by the time it’s done.

  15. Pete

    If they get bored at CERN they could test this idea in the LHC’s beam dump chamber.

    They’ll be like kids trying to think of stuff to shoot with their air rifle, but much more spectacular.

    “Hey guys…guys lets try a soda can!”

  16. Lyr

    Isn’t this how Dr. Manhattan came into being?

  17. chris

    to understand how the LHC REALLY works, you have to ask alpinekat.

  18. Gary Ansorge

    9. TCs

    Only 16 Teslas? Then I could be levitated with only a couple of hundred Ts.

    Bring it on,,,

    ,,,and thanks for the link. I was wondering how strong those B fields were.

    Now, how much mass compression can be achieved in a magnetic mirror? In other words, what’s the actual density of the deuterium plasma?

    When inserting hand into proton beam, be sure to use the non-dominant hand. You’ll need the other one for,,,Oh, never mind,,,

    Gary 7

  19. Gus Snarp

    Introducing me to this site is going to lead to a lot of lost productivity.

  20. Chris

    OK a little calculation time. My hand is ~1 inch thick, so assuming a density of nearly water (1 g cm^-3) and ~ 1 mole of nucleons/gram, we get a column density of
    (2.54 cm)(1g cm^-3)(1 mol/g)(6.022*10^23 nucleons/mol) = 1.5*10^24 nucleons cm^-2

    the cross section at 7 TeV is 110 mbarns = 110*10^-27 cm^2

    Multiply the two numbers is 0.17

    So each proton has about a 17% chance of a collision. It’s probably a little lower since I assumed everything was hydrogen atoms and not heavier elements, but order of magnitude is pretty close.

    Now what happens in a collision. Unlike the LHC, the center of mass of collision in your hand is not the same as our rest frame, so there would be significant momentum moving the particles forward. I don’t think the hand would explode, it might be more like the drilling scenario. So Kids don’t try this at home.

  21. Themos Tsikas

    They have a special beam dump place at the LHC: “Each beam dump absorber consists of a 7m long segmented carbon cylinder of 700mm diameter, contained in a steel cylinder, comprising the dump core (TDE). This is water cooled, and surrounded by about 750 tonnes of concrete and iron shielding. The dump is housed in a dedicated cavern (UD) at the end of the transfer tunnels (TD).”

    The energy in the entire beam is that of a TGV train going full tilt. If one thousandth of that is transferred to your hand, you’d still lose the hand. Then there’s the radiation from secondary reactions which will probably exceed lethal limits.

  22. Sarah

    There is a russian who managed to get his face in the path of a particle accelerator beam.

  23. Bethany (12): Interesting calculation! If you’re right, don’t forget that each beam has 3000 bunches of protons, so it’s not 0.001 grams, it’s 0.001 x 6000 = 6 grams. Not as big as what I found (where I assumed all the energy is absorbed) but still, bang! Ow.

  24. 1)
    2) Locally lethal from a second of exposure.

  25. MJD

    this page details (I think, it’s a bit technical) the protection mechanisms the LHC to prevent the beam doing damage if something goes wrong. about 1/3 of the way down there’s an image of what a proton beam from an accelerator can do to a copper plate. I imagine the effect on someone’s hand would be similar

    also, consider that the energy of the full beam is about 40 times the energy that produced the largest hole in that picture

  26. BCL1

    This is an interesting question. I used to work for a company that manufactured ion implanters (machines that accelerate ions and implant them into silicon wafers to make computer chips). Hitting silicon with an ion beam is well documented and can the effects of the incident beam on the target material can be modeled using Monte Carlo type simulations. There is a free program (I think that it is called TRIM or SCRIM or something like that — it’s been a while) that can be downloaded from the internet for this. I am not sure if it is applicable to the much larger energies used in the collider, however. My gut feeling is that most of the protons would pass right through your hand. However, some of their energy will be lost in the process. I’m going to look for the software and get back to you guys on this.

  27. CR (15):

    (without having seen the video link) Strangely, I’m reminded of a line from an early Star Trek Next Gen episode that went something along the lines of “Careful! That’s a strong enough magnetic field to suck the iron right out of your blood!” I’m guessing that might hurt a bit by the time it’s done.

    Or the episode of House, where he does an MRI on a corpse with a bullet in the skull.

  28. Xerxes

    I think the hand-beam question is best answered by this document:

    Granted, a carbon block isn’t an exact model of the human hand, but it’s probably close enough. The key points are:

    1) “this energy deposit over 85 μs is long enough to change the density of the target material. The density decreases at the inner part of the beam heated region because of the outgoing shock waves in the transverse direction. As an example, after the impact of 200 bunches with a size of σ = 0.2 mm, a maximum temperature of 7000K and a density decrease by a factor of 4 is expected.” The results of heating your hand to 7000K and increasing its volume by a factor of 4 are probably best not imagined. Since a full beam is 2808 bunches instead of 200, you might want to scale that by a factor of 10 too.

    2) But on the other hand (hehe): “The beam tunnels through the target and deposits the energy with a penetration depth of 10 m to 15 m” Since your hand is not 10m thick, you won’t pick up the full effect. This paper goes into some detail of the spatial distribution of the energy dump: So at hand-thickness of 2ish cm, you’d only get maybe an eighth of the effects of #1, so your hand will only reach the more modest temperature of 1000K (times 10 for a full 2808 bunches?). The shockwave from the blast will extend several cm in the transverse direction; translation, the rest of your hand will be blown off by the middle of your hand exploding. Probably the part of the accelerator apparatus downstream of your hand picks up the rest of the energy. The rest of you probably wouldn’t want to be standing next to it when it blows.

    Cool pictures of the effects of a low-energy (450-GeV) beam on copper plates are in

    (I spent so much time looking up references, several other people made the same points. Oh well.)

  29. BCL1

    Wow. I ran the SRIM simulation. There is no predicted interaction between the atoms in your hand and the proton beam. This means that the crossection for the hand/beam interaction is pretty much zero. The beam would pass through your hand like it wasn’t there. However, just becasue the beam woudn’t notice your hand, this doesn’t mean that your hand wouldn’t notice the beam. Even if a small amount of the energy available (a fraction of a percent) gets transferred to your hand (which seems likely in spite of what the calculations say), you will be in a world of hurt. Basically it would start to heat up really fast and burn a hole pretty quickly. If you have confidence that the simulation isn’t missing anything and that no energy is dissipated in your hand, however, you can try it. You first.

  30. Themos Tsikas

    Run the simulation again with something like the mass they use for dumping beam.

  31. Alan

    “He had his immortaility inadvertantly thrust upon him by an unfortunate accident with an irrational particle accelerator, a liquid lunch, and a pair of rubber bands. The precise details are not important because no one has ever managed to duplicate the exact circumstances under which it happened, and many people have ended up looking very silly, or dead, or both, trying.”

  32. BCL1

    I am not sure what they use for the beam dump. Typically we would use carbon as this would sputter very little and would conduct a far amount of heat. Given the high energy of the beam they are using, I am not sure what they use for a beam dump. Do you know?

  33. JAMarton

    I’m ashamed to say that one day while doing dishes I wondered whether a particle accelerator could clean my lasagna pan. Thanks for the post!

  34. BCL1

    Ah, now I am reading a few more of the posts. Xerxes has some interesting information and appears to be the final word in this discussion. I don’t think that the simulation program that I’ve been running is designed for these high energies and is probably lacking into taking into account secondary effects which dictate energy dissipation when the energies are very high and the crossection of the interactions are low. Relativistic effects may also come in to play and I know that the simulation model does not cover these. I see that they are using carbon as a beam stop and that the thickness is 15 meters! I actually plugged in 10 meters when running a model and it didn’t make much of a difference. There was still no interaction between the beam and the carbon beam dump as there should be. When the model no longer agrees with observations, it’s time to formulate a new model.

  35. Xerxes

    @BCL1: I think the program probably does not correctly scale, since a very high energy proton beam will interact primarily through strong interactions rather than electromagnetic. The electromagnetic interactions would be almost negligible, as you computed.

    The beam dumps are carbon. They keep it from heating up too much by using magnetic dissipators to spread around the beam energy.

  36. Bryan

    As a wise man once said “Don’t be so arrogant- 98% of you is water and most of the rest is the space between electrons”

  37. Grizzly

    What appealed to me about this was the “Gee, I don’t know” aspect rephrased a half dozen times for each question… and the “But, let’s see… umm, well, here’s a thought…” that followed each question.

    Then there was the difference in opinion, and in some the excitement about trying to figure out an answer.

    That’s science there, the “I don’t know, let’s find out…” Assuming that we can construct an experiment to test hypotheses then we’re able to learn and have fun with the question.

    And that’s why I’m hoping the scientists on the LHC begin to find answers because I really don’t like untestable hypotheses (string theory being one).

  38. Rob Ingram

    This isn’t just theoretical for me. I’ve had my head in a proton beam. Now obviously not one as powerful as the LHC, of course. I was a patient the M.D. Anderson Proton Treatment Ctr. in Houston. The energies used to treat a tumor in the base of my skull was only in the range of 70 to 250 MeV. The interesting thing about protons versus X-rays is how their “dosages” are distributed through tissue depth. The good thing about protons is that they don’t ionize through the entire depth of the body as X-rays do. That’s also the bad thing as the higher the energy, the deeper the penetration depth and also the higher the resulting ionization.

    I definitely don’t think it would be a good idea, but I don’t think there would be a “Bang!”.

  39. Rob Mutch

    A great video. I really enjoyed getting the different perspectives of each scientist – a mix of their knowledge and personal feelings.

  40. TRL

    I can’t speak to the LHC, but during a visit to SLAC in the early 80’s, the guy showing me around showed off a steel ingot into with they dumped the electron beam out of curiosity. It was completely disrupted. I would not put my hand into the beam.

  41. Gerry

    Sounds like a job for Cadaver Hand.

    Should be pretty easy to get one from the nearest University medical school….

  42. Owen

    My first reactions go something like this:

    What would happen? Besides quenching? And giving a lethal dose of radiation to the person? And how the heck did that person get past the safety systems anyway? Someone escort this person to medical immediately!

  43. Now, that’s going to leave a mark!

  44. Andrew Barton

    I think we need one of those signs, like the ones they have for lasers …

    ‘Do not put remaining hand into beam of LHC.’

  45. Steve Caron

    This is facinating.

    The biggest detractors of the LHC have stated that it shouldn’t continue because the scientists don’t really know what will happen and it isn’t worth the risk.

    And here they are, admitting they have no idea what would happen.

  46. I love watching geeks figure out thinky stuff.

  47. JoeSmithCA

    Hey if I’m going to do something dumb like put my hand in there I’m going to prove or disprove the whole liquid nitrogen thing then a bottle of liquid hydrogen and if I’m still alive maybe kilogram of C4 wrapped around a stick of dynamite. I figure between any of them I should get quite a bang out of it.

  48. Ray

    Maybe its the kid in me, but why don’t they just test this with a fresh pig’s knuckle? (avoids the thorny issue of using human remains for experimentation)

    Really, what is the LHC doing on the weekends? Get a couple of guys together and let them see what happens during the down time.

    Oooooh, better yet, send this to the Mythbusters and let them test it. Phil, Adam Savage is your bud, hook us up!

  49. Buzz Parsec

    @Uncle Al (27) –

    ” I’ve written about a 100,000 lines of PDP-11 assembler code and would never set a flag by incrementing it while assuming it’s clear. The right way to set a flag is to clear it and then complement it (CLR(B) FLAG, COM(B) FLAG) if the tested for condition obtains. If you want to set the flag unconditionally, and are really pressed for space, MOV(B) #-1,FLAG does it in one instruction and in one less memory reference and word of code than the CLR(B) FLAG, COM(B) (or INC(B)) FLAG sequence. NEVER blindly assume that FLAG is initially clear. If and only if all code paths have been inspected, a comment explaining the situation is absolutely mandatory. And this applies to my code, none of which is real-time or used in life-critical contexts. In a machine capable of killing people, every single line of code should be checked and all assumptions must be thoroughly documented in the source, and any maintenance must recheck the assumptions and update the documentation as needed.

    If it was really a counter and not a flag they were incrementing, of course they need to check for overflow after each increment.

    To everyone else, I don’t often get a chance to rant about PDP-11 programming anymore, so I couldn’t resist temptation. Just be thankful I stopped after one!

    PS. Does anyone know how to quote angle brackets so you can make fake HTML tags look right?

  50. DNash

    This question reminds me of a time in 7th grade math class where us smart aleck kids tried to distract our teacher from the boring lesson by asking him a question from comedian Steven Wright’s show: “If you’re driving in your car at the speed of light, and you turn your headlights on, would they do anything?”

    The teacher, not realizing this was a joke, actually tried to answer and took up about half the class period.

  51. jaranath

    Gus Snarp @#5:

    Harun Yahya (or his organization) sent the Atlas of Creation to a LOT of scientists, gratis. Probably was one of those. I know I want a (free) copy!

  52. Luke

    @5. Gus Snarp

    He actually took the time to explain why he had the Atlas of Creation in another video (a fan asked this exact same question), which I can’t seem to find at the moment, but essentially, your assumption about debunking is correct, plus he said something about finding the illustrations beautiful if I remember correctly.

  53. Asura

    What happens…?

    The best Mythbusters episode evar!

  54. Sharku

    @Bethany: Prof. Copeland mentions the protons having a kinetic energy of 7 TeV (10^12) yet you seem to be using 7 MeV (10^6) in your calculations, so… am I missing something or are you?

  55. TJ

    I swear there was someone that got hit by a weaker particle accelerator back in the day, hit him in the face, messed him up baaad.

  56. kevin

    Wow… honestly listening to these people talk makes me realize just how stupid I am.

    Great stuff.

  57. I had a thought and the video seems to have mentioned this, but the inside of the accelerator is a vacuum. If you were to somehow open the tube and stick your hand in, that would let the surrounding air rush into the tube and probably cause the beam to greatly decohere and lose most of its energy before you could do anything. Although the Bremsstrahlung radiation from that might be deadly.

  58. Adrian

    A pity Mythbusters doesn’t have the budget to test that. :)

  59. Kaleberg

    My old high school actually had a cyclotron. We could have tried a low energy version of this experiment.

  60. Messier Tidy Upper

    Great questions – and answers in that videoclip. Fascinating. :-)

    Just one comment of mine to add which regards the supernova segment of the video – we now think Betelgeuse is further than 400 light years – at least another 100 and possibly more. Stellar expert Jim Kaler suggests 570 ly :

    But it could be as far as 640 light years distant, the figure indicated by its natural radio emission parallax. (No, I’m not sure why Betelgeux’s parallax would be different in radio vs light or other electromagnetic radiation.)

    Also it seems everyone forgets about the type Ia “white dwarf” supernova!

    If our Sun had an extra half a solar mass or so .. plus a nearby interacting companon star to gain matter off .. and was already a white dwarf star (which it will be give a five or so billion years) then we might be talking! 😉

    Except, of course, it isn’t, it hasn’t got a companion star to gain mass and when it eventually does become a white dwraf it won’t boast one solar mass anymore but very much less!


    PS. My favourite symbol personally is Pluto’s juxtaposed ‘P’ & ‘L’ combining the planet’s initials with a subtle reference to Percival Lowell who worked and funded its search – and the Lowell observatory from where Tombaugh discovered the long sought Planet X. :-)

  61. Bethany

    @ Sharku (58) I appear to be missing something. I calculated the energy using the Lorentz factor from wikepedia. However, the article also states the energy to be 7 TeV. Missing by a magnitude of 10^6 will make a big difference in what’s going to happen to your hand.

  62. ggremlin

    I’m disappointed, 66 comments and not one Ghostbusters reference or even Real Genius?

    The math is beyond me, but I would say “Nothing Good” is an acceptable answer. :)

  63. ctcoker

    Honestly, I really don’t know that it would do much besides possibly give you cancer. Following Bethany’s calculations, it seems that the closest analogue would be an intense beta source. These will burn you, and obviously can kill through prolonged exposure, but burning holes in your hand and such? I don’t think so.

    However, if we take Phil’s comment on the aforementioned work, we would get about 25 kJ of energy deposited in the hand (the 5 J from Bethany is going to do jack and squat in terms of large scale effects, by the way). A human hand masses maybe a quarter kilogram, and has similar properties to water (seeing as it’s abut 3/4 water in the first place). This water starts at about 40 C, so if we dump 25 kJ into the hand at once, we end up with a ~25 C degree rise is temperature. This would probably result in a bad burn. But the LHC beam is not 10 cm wide, it’s maybe 10 mm wide at its widest. Armed with this information, we’re dumping 25 kJ into maybe only ~1/50 of the hand’s volume and mass, so we end up boiling the water in the hand in the beam path (latent heat of vaporization for water is 2.2 kJ/g, and about 10 grams of water is in the beam path). Ouch. So yeah, maybe the beam CAN burn a hole in someone’s hand.

  64. Agt_Grey

    Oh great… now Jamie and Adam are gonna start building a particle accelerator for Tory to stick his hand in. Does no one think these things through?!?

  65. Raskolnikov

    Oh oh… This reminds me of the time I played… I mean experimented with liquid nitrogen and an empty bottle of Sprite…

  66. JibJab

    This is the difference between science and religion. One asks numerous questions, compares their results to others, and ponders the result at length. The other says “God did it!”

  67. Gus Snarp

    @Luke – Thanks, I am reassured. I’ll be working my way through the backlog of videos, so I’m sure I’ll see that one eventually.

  68. Nigel Depledge

    BCL1 (29) said:

    My gut feeling is that most of the protons would pass right through your hand. However, some of their energy will be lost in the process.

    Yeah, I think if the beam did pass through without hitting any nuclei, the protons would still emit Cerenkov radiation on the way.

  69. Nigel Depledge

    Xerxes (31) said:

    Granted, a carbon block isn’t an exact model of the human hand, but it’s probably close enough.

    Given that the human body is about 70% water, I think a bucket of water would have been a closer model.

  70. Nigel Depledge

    @ Alan (34) –
    Ah, yes, poor old Wowbagger (the Infinitely Prolonged)

  71. Nigel Depledge

    Bryan (39) said:

    As a wise man once said “Don’t be so arrogant- 98% of you is water and most of the rest is the space between electrons”

    Cucumbers are 98% water. People a bit less (about 70%).

  72. Nigel Depledge

    TRL (43) said:

    I can’t speak to the LHC, but during a visit to SLAC in the early 80’s, the guy showing me around showed off a steel ingot into with they dumped the electron beam out of curiosity. It was completely disrupted. I would not put my hand into the beam.

    Hmmm … probably not a very accurate parallel.

    The commonest atom in steel is iron, which is a pretty big nucleus (although I’ve no idea what its cross-section is in barns).

    The commonest atoms in a human body are hydrogen, carbon, oxygen, nitrogen, phosphorous, sulphur, calcium, sodium, and potassium. Iron, zinc and chlorine are in the mix too, but at a lower abundance. Although, again, I’ve no idea what kind of cross-section these have in barns.

  73. Rizz Rustbolt

    Sounds like a job for the Mythbusters.

  74. How long has René Auberjonois been working on the LHC? 😉

  75. Partial to Particles

    Here is a quick calculation (with the LHC at full design energy and intensity, if they ever get there):

    Protons with that energy are roughly “minimum ionising”, depositing about 2 MeV/g/cm**2 locally by ionizing atoms.

    The human hand is about 1 cm thick and is mostly water, density 1 g/cc (convenient!!)

    So 1 proton will deposit 2MeV locally in your hand.

    There are 10**11 protons/bunch, and about 3000 bunches around the LHC ring, so in 1 turn of the ring
    3×10**14 protons pass through your hand, depositing 6×10**14 MeV.

    1 ev is very roughly 10**(-19) Joules (J)

    So, 1 turn of the LHC deposits 10**(-19)x6x10**14×10**6 J = 60 J

    1 turn of the LHC takes only ~100 microsec=10**(-4)second, so you might think if you stuck your hand in for 1 second, say, the protons would come through your hand 10,000 times. However, there is another effect on the protons going through the material in your hand called “multiple scattering”, which will blow up the beam enough that it will be all lost after a few turns (I would need some computer code of the beam optics to see how many a few is).

    Let’s take a few to be 2 turns, so we have about 120 Joules deposited in your hand. That is not a lot, but since the beam is, say, 1 mm square, the energy is deposited in 0.1×0.1×1 cm**3 = 0.01cm**3 of your hand.

    Now, the heat of vaporization of water is about 2000 J/cm**3, so the heat needed to boil your blood in that local region that the beam passes through is only 2000 x 0.01 = 20 Joules, much less than the 120Joules deposited by the beam. Some of the heat will spread out by thermal conductivity, but since it is deposited in such a short time, about 100 microseconds, I think the blood will boil locally causing vein rupture etc, and likely quite a nasty burn and mess. “Drilling a hole” through your hand is probably not far off the mark.

    Another effect is that some of the protons will actually interact with nuclei of the atoms of your hand. For a 1 cm hand this would be very roughly 1 percent of the beam particles. The 7 TeV of this nuclear collision will mostly go forward, but maybe about a fraction 0.001 would go sideways and some of it, say about 10%, would be absorbed in your body. So, this would be about 7×10**12x.001x.01×0.1x3x10**14×10**(-19)= 210 Joules, probably an overestimate. Anyway, this would be deposited over about 50kg of body mass, or about 50,000 cm**3, so about 0.004 Joules per cc, not enough to boil you. However, it is a LOT of radiation, 4 joules/kg=4Gray, the unit of radiation absorbed dose. A radiation worker has a legislated yearly limit of about 200 times less!!!

    Conclusion: stay away from the LHC beam…

    PS, I haven’t checked my arithmetic thoroughly…

  76. ColonelFazackerley

    I did my undergrad at Nottingham.

    The chap that mentions synchrotron radiation is Professor Moriarty. Really.

  77. bob

    all you people are FAIL.

  78. nymonym

    Who are the physicists here? Does anyone know their names?

  79. Mitchell

    The quality of the LHC beam question responses illustrates a larger problem. Aside from people having difficulty giving ‘back of the envelope’ answers to unexpected questions.

    “What would happen if I touched it?” seems a primal question of common interest. One might think education content on any topic, LHC beam, vacuum, intense B fields, cryo, anti-matter, supernovas, hot Sun, dark sky, whatever, would touch on it. But no. While of educational interest, it’s rarely of research interest.

    Questions of educational interest, however great, but little research interest, rarely end up as educational content. “Easy to state, but hard to answer, requiring consideration of many things” is typical. As is “a puzzle, easy to get wrong”. Requiring collaborative work and peer review. Which, absent research incentives, doesn’t happen.

    “Silly and frivolous” questions aren’t the problem. Take any topic, pose a handful of questions laying bare its deep structure, and commonly, answering them requires recourse to primary literature and talking with domain experts. Educational content being composed of the stories easily found, and thus pervasively superficial, outdated, badly incomplete, and incorrect.

    Bluntly, the dreadful state of descriptive science education content, K-grad, is a failure of the scientific community, not the education community. They have their own problems. But the inability to build content around the “simple and profound”, the insightful and compelling, merely because it’s hard, interdisciplinary, there are few incentives, and we can’t be bothered? That’s our problem.

  80. Montana

    Great clips. Very inspiring last section.

  81. RCT

    Completely unsurprising that these scientists have totally inadequate radiation safety training regarding the collider and obviously none have been trained on the simple fact that direct exposure to the beam would cause extreme damage to any tissue exposed.

    These aren’t neutrons and don’t need to collide with nuclei to cause an ionizing radiation cascade in tissue. I’ve never seen SI tables for TeV particles but based on typical transuranic alpha SI’s I would not be surprised if each event was a multi-cell-killer.

  82. Once again, science fiction die it first. In “Star Smashers of the Galaxy Rangers” the main characters create a new material by placing a piece of cheddar cheese in a cyclotron. The result, “Cheddite” is used in a new, ultra powerful star drive…

  83. Once again, science fiction did it first. Just as Arthur C. Clarke predicted communication satellites, Harry Harrison predicted something like this in “Star Smashers of the Galaxy Rangers”. The main characters jokingly replace the target in a cyclotron with a chunk of Cheddar cheese. The resulting material, “Cheddite”, creates a powerful new star drive…

  84. Adam F

    As a biologist, my go-to guess would be that you would get cancer if you stuck your hand in something like that. DNA doesn’t like high energy particles blazing through it. I’m all for attempting to cook a ribeye though. Science for the lulz!

  85. meekGee

    I read somewhere that the centrifugal force exerted on the tube is actually measurable.

    Somewhere, in the vacuum, the quantum sound of 400 Billion femto-tires is echoing down the tubes, like a lone car in the Lincoln tunnel at 3 am.

  86. fooburger

    I was going to point out that Bethany’s calculation significantly underestimates the energy (MeV instead of TeV), but it looks like she already caught it.
    What’s the cross section of a TeV proton in meat?
    Normally when I want cross sections and stopping powers I look at NIST tables.
    Unfortunately there aren’t a lot of TeV proton sources to provide empirical data on this.
    Generally the hotter a species is, the less ‘collisional’ it is, so while there’s more energy to ‘give away’, the particle also becomes less and less willing to give that energy away.

    I generally visualize this as a ‘Coulomb’ interaction between two charges. When the charges are approaching each other very quickly, the ‘Coulomb’ force acts on each charge for a more limited amount of time than when they are passing by slowly. The Coulomb force itself doesn’t change much, but being that the time interval is smaller, then the change in energy of the particles is going to be small.

    And beyond that:
    – Is there a Bragg Peak for TeV protons? Is it significantly different from MeV protons? (If I recall, protons lose energy roughly linearly until they get below a threshold, at which they become highly collisional and deposit their energy all at once. It may be that TeV and MeV protons deposit the same energy into a ‘hand’.
    – If protons lose energy by passing through your meat-hand, will they de-phase from the synchotron and go careening about? Or is the LHC pretty flexible and not a finely-tuned highly-unstable device? How important is timing in the LHC?

    Some of this makes me wonder whether the vacuum is perhaps only necessary during acceleration of the particles?

  87. Frank Van den Heuvel

    Never heard of proton radiation therapy? It is a well known problem to all radiation therapy physicists out there. The energy is so high, almost no direct interactions with the electrons (ionizing)
    takes place. The amount of nuclear interactions could increase somewhat and probably cause some damage. In a nutshell direct dose deposition equals Stopping Power (amount of energy deposited per unit length) divided by the mass and Stopping power is inversely proportional to the square of the particles speed (for charged particles). As these particles are so high in energy the stopping power will be low. Probably a 50MeV proton beam would be more effective in depositing its dose for a hand.

    Hope this helps

  88. @51: what the LHC does on weekends (and nights, and other times..) is: more experiments. It’s a 24/7 operation with people working in shifts. If you want to peek, visit (for example)
    I enjoy the technical terms they use, they could describe a whole new spaceship for startrek.

  89. sanskritter

    73. Raskolnikov Says:
    September 22nd, 2010 at 12:11 am

    Oh oh… This reminds me of the time I played… I mean experimented with liquid nitrogen and an empty bottle of Sprite…

    … not sprite then is it?

  90. Mike O

    What is C-A-T really spelled DOG?

  91. J

    Intern cleanup, lol.

  92. HBT

    Why don’t they just put a hand and see what happens. There are plenty of morons who would volunteer for it. If it destroys the solar system then one good thing is you don’t get people asking questions like this …

  93. DSC

    Mythbusters time!

  94. In 2003 a malfunction in the Tevatron caused the beam to drill a hole in a couple of the magnets. If it hits your hand, expect something similar. A small hole in the palm, the rest of the hand gets barbecued from the heat and the rest of the body gets irradiated.

    This is exactly what most sci-fi rayguns do to a body, except for the radiation thing.

  95. Felicia

    Just put a ham in the path of the beam and see what happens. Get an experimentalist to answer this!

  96. Xerxes

    Not sure if anybody is still reading this thread, but there are some new interesting references to consider. This talk by Alessandro Bertarelli at Chamonix has what must be the world’s most informed discussion:

    Unfortunately, the primary literature on this topic tends toward steadfastly practical discussions of “Would this part of the apparatus be deformed by more than 10 microns and need replacement?” rather than “How cool would that explosion look?” However, it contains (on page 16) an entertaining simulation of 45 microseconds in the life of an unfortunate tungsten collimator under the impact of a mere 8 bunches of beam. I think they don’t bother to simulate worse than that because at 8 bunches, you already have the spattering molten tungsten perforating the vacuum pipe and causing a cascade of catastrophic failure.

  97. I have a silly question, that arose when I was watching a Ted talk by Brian Cox, in which he says the beams travel at 99,9999% the speed of light. The number of 9’s after the comma is arbitrary?

  98. Kristopher

    God, i plan on being a physicist and the favorite symbol question would have been a bit embarrassing as i would have automatically said the triforce.

  99. George McIlvaine

    It is interesting that the question is not really answered. It’s a reasonable question. Instead of even a first order guess, we are given “It’s complicated,” and “There are a lot of factors.” It shows unwillingness to risk being wrong, and actual ignorance beyond narrow scientific specialization. And when one asks a question like that, the response comes with an implied smirk about our scientific naiveté. Well, yes, we are naive, and scientifically unsophisticated in the area of advanced subatomic particle physics. But here’s the thing… we, all of us, live in the same world as the LHC scientists. And some other scientists have expressed concerns about the possible global consequences of LHC experiments. Whom should we believe… people who can’t answer a simple question but mock others’ ignorance? Bravo to those posting their speculations, calculations and models… thank you for trying.

  100. Carlos

    The curious thing bout this video is how they cannot help to over think the question, for example, the one about a star going supernova close to us, the question is not “Can a star go supernova close to earth?” which is the one they are answering, the question is “What would happen if a star went supernova close to earth?”, they cannot accept this ilogic question!! just ask them, if a planet just like earth, with animals and atmosphere and magnetic field were close to a star, and that star went supernova, what the hell would they experience?!! And they say they have nothing like the Big Bang Theory guy!!!

  101. Max

    I noticed that a lot of the scientists don’t really answer the questions directly or they’ll rephrase the question to fit their response.

  102. Digger

    I think all of this must be very dangerous at last.
    And army have own interest here.


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