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I have a question regarding creation of anti-matter

  1. Sep 22, 2007 #1
    I have a question regarding anti-matter in which ways can it be created? I got into a heated arguement with someone last night. He's a first year university student and he was trying to tell me that we can create it by accelerating particles to the speed of light and making them collide. I know for a fact this is false because only light can travel that fast. I also read something about Gamma rays hitting earths atmosphere and creating small amounts of it could this be what he's talking about? gamma rays are made of protons correct?
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  3. Sep 22, 2007 #2
    Gamma rays are high energy photons - not protons.

    Your first year university student was correct. Most antimatter particles were discovered in particle accelerators (http://livefromcern.web.cern.ch/livefromcern/antimatter/). Obviously you cannot accelerate particles to the speed of light - but you can accelerate them to relativistic speeds (very close to the speed of light). When you collide these particles you can create positron emissions among other things. That is the technology behind PET scans.

    Also - Positrons are also produced from the radioactive decay of nuclides such as carbon-11, nitrogen-13, oxygen-15, fluorine-18, and iodine-121.

    Also - you are correct about high energy collisions in the earth's atmosphere creating antimatter.
  4. Sep 22, 2007 #3
    sorry I ment to say photon lol I at least know the basics but....

    hmmm what if you had two particles traveling 80% the speed of light would the other particle not seem to be going 160% the speed of light towards you from the perspective of the particle.
    Sorry lol I know this has kind of become a question of relativity but I guess thats a big part of astronomy.
    thanks for clearing up how Positrongs are created.
  5. Sep 22, 2007 #4
    Cosmic rays are usually high energy protons. Aren't PET (Positron Emission Tomography) scans dependent on detecting the antimatter component (positron) of (inhaled) radioactive oxygen having decayed, not man-made collisions?
  6. Sep 22, 2007 #5


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    Yes, I think you are right. The positrons used in a PET scan are created in a radioactive process. If your PET scan involves putting your head into a particle accelerator, your going to the wrong radiologist.:biggrin:
  7. Sep 23, 2007 #6
    I meant that PET scans used positrons (antimatter). I didn't know where the positrons came from - thanks for clearing that up.
  8. Sep 23, 2007 #7
    So long as I'm not more confused than I think: Yes, from your point of view at least. But from the point of view of either particle, the answer would be no.

    Check this out: http://www.math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html

    You don't add velocities the way you'd expect to. At speeds we normally travel, it makes no difference. But closer to the speed of light, it makes a huge difference.
  9. Sep 23, 2007 #8


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    As an interesting (I hope) sidenote, I've read that turbulance on the surface of the Sun creates antimatter in a process vary much like that in particle accelerators. One sunspot was observed to have created more than a pound of the stuff! (Indercetly observed, of course.)
  10. Sep 23, 2007 #9


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    PET scans detect the 2 anihilation photons (0.511 MeV) when the positron-electron anihilate each other.


    High energy particles, e.g. protons in the GeV range can produce antimatter-matter pairs when colliding with other nucleons. The total energy must exceed the rest energies of the particles created and reacted.


    Cosmic rays are generally high energy protons, but there is actually a spectrum.

  11. Sep 25, 2007 #10
    We all know that mass = energy, but at least most of the time it seems more specifically that energy = 1 part matter + 1 part antimatter. So if you accelerate two particles (i.e. add energy), then stop them, that energy is liable to come out as half antimatter. But I'm getting more and more confused trying to decide how general a rule the matter + antimatter part is.

    Now I remember some idle conversations ten years back where I was supposing that if you took a tiny black hole and force-fed it a concentrated stream of matter, while it was busy spraying out Hawking radiation, that you'd manage to convert matter into matter+antimatter, which would be a neat trick. But I know some things have come out about correlations in Hawking radiation since then - I don't know if this one works.

    Then there's radioactive decay, where something like 0.4% of the mass in uranium comes out as energy. But maybe that has something to do with the W being its own antiparticle? Wait, no, that's the Z. I really should review my particle physics sometime.

    Now here's where I realize I'm totally clueless. Kinetic energy and potential energy are two interconvertible quantities, right? A particle with kinetic energy has extra mass... does a particle with potential energy have extra mass? If I have a pet double neutron star in my backyard, do the two of them increase their gravitational pull every time their highly elliptical orbit brushes them past each other at "almost" the speed of light? Or do they get extra mass from being far away from each other the same way as they get extra mass for moving fast - but then why don't they have infinite mass from being infinitely far from practically everything in the universe.

    Oh, bother. I don't even remember forgetting that one.
    Last edited: Sep 25, 2007
  12. Sep 26, 2007 #11
    so you mean 2 particles heading towards each other, each individual particle going at 80% the speed of light? When people think of light speed and Einstein's saying that nothing can break c people usually think of some type of situation like 'If I were hanging onto the back of a train going at the speed of light..." but they neglect to include the other brilliant part of Einstein's theory dealing with time's inconsistency and the Lorentz Factor. Logically, two particles zooming at each other each at 80% of c would, by the intuitive logic of Newtonian mechanics, be going towards each other at 160% c but this is not the case because from the reference point of a particle, it is going very fast, and because it is going very very fast relative to the other particle, time is very very slowed, slowed to the point at which the rate they approach each other is in fact less than c
    Last edited: Sep 26, 2007
  13. Sep 26, 2007 #12
    By virtue of the facts that light speed is constant and maximal, and that light is our standard of measurement and communication, the Lorentz factor follows naturally from little more than these and the Pythagorean theorem. Also, through special relativity all physics in inertial ("not relatively accelerating") frames transform directly into each other.
  14. Sep 26, 2007 #13


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    Precisely because "you don't add velocities the way you'd expect to", you would not see the two particles moving at 160% the speed of light "from your point of view".

    If particle A is moving at 80% the speed of light, relative to you, and particle B is moving at 80% the speed of light, relative to you, directly at particle A, then you would see that the two particles had a relative speed (relative to each particle) of
    [tex]\frac{.8c+ .8c}{1+ \frac{(.8c)(.8c)}{c^2}}[/itex]
    (That's the formula ganstaman was referring to.)

    You should be able to calculate that that is 1.6c/(1.64)= about 97.6% the speed of light. Still less than the speed of light.
  15. Sep 26, 2007 #14
    HallsofIvy: Oh, I see where I went wrong. This line from the link: "Originally we wanted to know the speed of C as measured relative to A not the speed at which B observes them moving together."
  16. Sep 26, 2007 #15


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    Just to be sure understand you:

    If I see two particles that are at locations which I measure to be 10 light-minutes apart, and I see them as moving toward each other (and toward myself), each at a speed of .99c (from my perspective), my watch will still count off more than ten minutes before I see them collide?
  17. Sep 27, 2007 #16
    Assuming I've finally got this, the answer is no. Read my above post. There's a difference between the speed at which we see the particles moving together and the speed of one particle relative to another as we measure it.
  18. Mar 14, 2011 #17
    Re: AntiMatter

    even if you had many massive particles firing at each other, the equation shos they can never reach the speed of light, it can get infinately close to the speed of light but never quite reaching it :)
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