Results 1 to 13 of 13

Thread: Matter-Antimatter rocket - gamma rays and such

  1. #1
    Join Date
    Feb 2003
    Location
    Depew, NY
    Posts
    6,525

    Matter-Antimatter rocket - gamma rays and such

    What do gamma rays do to matter? Do they weaken materials, heat them up or make an electric charge?

    If an matter-antimatter rocket malfunctioned so that it was not mixing the matter and antimatter correctly, would you have to worry about unreacted particles looping back towards the ship at high speed? Could you actually have M-AM reactions happening far behind the rocket?
    Solfe

    -----------------------------------------------------------------------------------
    "Triangles are my favorite shape
    "Three points where two lines meet"
    Tessellate, Alt-J

  2. #2
    I'm not the best informed person, but I can attempt some answers. I'm pretty sure gamma rays are photons, so they would not have any effect on the electric charge. What they do is they strike atoms and make the electrons gain energy, so I think that they would heat them up. And they can make atoms lose electrons (ionization), so that would be damaging.
    As above, so below

  3. #3
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    19,916
    I might know more than Jens (or not), but I can say a little more. As he says Gamma Rays are photons. The positron-electron interactions give off 511 KeV photons which are not energetic enough to disrupt stable nuclei, but can ionize atoms a few eV at a time, so one annihilation would ionize maybe 100,000 atoms... which would make things hot, and disrupt crystaline structures and alter chemical bonds making complex things like DNA lose information. The proton-antiproton annihilation gives off three gamma rays, which average about 600 MeV. These are above the threshold needed to create pions and other mesons, and so do have the ability to disrupt stable nuclei, potentially freeing protons and neutrons from heavier species... but also result in a lot of ionization events creating heat, and disrupted chemical bonds.

    There are several ideas I've seen for how a matter-antimatter reaction could power a spacecraft, but none have been highly efficient at converting energy into a change in momentum. It's usually just trying to maintain a certain temperature of plasma, and using a hole in a magnetic bottle to direct particles out the back. So, with such a model, having to rich a mix of anti-matter could result in spraying expensive anti-particles out the back unreacted (maybe)... but as long as the magnetic confinement stays operational, you shouldn't have anti-matter leaking forward into your payload... and a modest amount of shielding should keep the 600 MeV gammas from hurting the payload either.
    Forming opinions as we speak

  4. #4
    Join Date
    Feb 2003
    Location
    Depew, NY
    Posts
    6,525
    I am writing a story where the characters attempt to put too much matter and antimatter fuel on their shuttle and it wrecks their engine in a scary and annoying way.
    Solfe

    -----------------------------------------------------------------------------------
    "Triangles are my favorite shape
    "Three points where two lines meet"
    Tessellate, Alt-J

  5. #5
    Join Date
    Jul 2006
    Posts
    9,072
    On the other hand it sounds like one of the most efficient warhead payloads you can come up with for the weight and space.

    Makes the most energetic chemical explosives look like mentos and diet coke.

  6. #6
    Join Date
    Nov 2005
    Posts
    3,448
    All those are engineering concerns. I presume that a partical of antimater has to come within about a pico meter of some regular matter to be aniallated. If that is more than rarely the surface of the exhaust cone, then frequent repairs will be needed. Yes some will aniallate far behind the exhaust nozel. I presume a positron can be anihalated by a nucleus with no electrons.Tail gating a matter-antimater engine would be a disaster. CNT = carbon nano tubes with great specs loose strength rapidly with really minor changes in the crystal latice. Anti-protons being aniallated may produce much more energetic gamma photons. Neil

  7. #7
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    4,171
    I presume a positron can be anihalated by a nucleus with no electrons.
    You would be wrong

    I presume that a partical of antimater has to come within about a pico meter of some regular matter to be aniallated.
    Remember - they are charged and attract each other. Positronium is something like 100 picometres across.

  8. #8
    Join Date
    Feb 2005
    Posts
    8,018
    I thought this was noteworthy:

    http://io9.com/5889828/were-on-the-v...er-discoveries

    "The other big antimatter-related result hasn't come from a big particle accelerator but instead a nanowire in a Dutch laboratory. According to a team led by Leo Kouwenhoven of the Delft University of Technology, they have spotted what could be the first experimental evidence of Majorana particles, first proposed by Ettore Majorana over 70 years ago."

    "These theoretical particles are a unique exception to the standard relationship of matter and antimatter, in that they don't annihilate each other when they come into contact. Majorana realized in 1937 that a fermion with no electric charge would have a completely identical antiparticle, meaning pairs of these particles would be able to exist together without destroying one another. They're remained strictly theoretical until now, when Kouwenhoven reported the first tentative evidence of their existence."

    Also:
    http://en.wikipedia.org/wiki/Onium
    http://en.wikipedia.org/wiki/Orthopositronium

    So maybe we have a way of storing the stuff. To loosen things up, use it to spike the jet of a NSWR to get a reaction going--the very jet used as containment?

  9. #9
    Join Date
    Jul 2011
    Posts
    496
    Quote Originally Posted by publiusr View Post
    So maybe we have a way of storing the stuff. To loosen things up, use it to spike the jet of a NSWR to get a reaction going--the very jet used as containment?
    But if these identical pairs peacefully co-exist, what's the point?

    Quote Originally Posted by antoniseb View Post
    I might know more than Jens (or not), but I can say a little more. As he says Gamma Rays are photons. The positron-electron interactions give off 511 KeV photons which are not energetic enough to disrupt stable nuclei, but can ionize atoms a few eV at a time, so one annihilation would ionize maybe 100,000 atoms... which would make things hot, and disrupt crystaline structures and alter chemical bonds making complex things like DNA lose information. The proton-antiproton annihilation gives off three gamma rays, which average about 600 MeV. These are above the threshold needed to create pions and other mesons, and so do have the ability to disrupt stable nuclei, potentially freeing protons and neutrons from heavier species... but also result in a lot of ionization events creating heat, and disrupted chemical bonds.
    Essentially, weakening most structural materials.

    There are several ideas I've seen for how a matter-antimatter reaction could power a spacecraft, but none have been highly efficient at converting energy into a change in momentum. It's usually just trying to maintain a certain temperature of plasma, and using a hole in a magnetic bottle to direct particles out the back. So, with such a model, having to rich a mix of anti-matter could result in spraying expensive anti-particles out the back unreacted (maybe)... but as long as the magnetic confinement stays operational, you shouldn't have anti-matter leaking forward into your payload... and a modest amount of shielding should keep the 600 MeV gammas from hurting the payload either.
    What of the idea of using the fuel, or at least reaction mass, as shielding? Pure energy isn't a very effective reaction mass, and neither is the fact that half the energy produced is released as neutrinos, essentially worthless as either reaction mass or as usable energy.

    What reaction mass is both abundant throughout our universe, easily collected (Bussard's Ramjet) and also capable of being used as shielding against gamma rays? How about liquid hydrogen? Wouldn't H2 in liquid form be useful? I'm not talking about using Bussard's device as an engine. Just a collection machine.

  10. #10
    Join Date
    Feb 2003
    Location
    Depew, NY
    Posts
    6,525
    Just to flesh out my why I asked the question - What I was picturing was a shuttle that uses an antimatter rocket for propulsion. The engine exhaust and the shuttle itself is more of a hazard than any weapon it carries. The crew of the shuttle needs to escape from a hostile but not well armed larger spaceship. The larger ship wants to re-capture the shuttle crew (mostly) intact. The main concern of the shuttle crew is making sure they do not fly into the larger ships exhaust and do not stray into the larger ships best weapons arcs. If the shuttle can accelerate fast enough, the large ship will not be able to chase them down easily and will give up.

    The shuttle normally carries 20 grams of antimatter when fully loaded but in the current scenario the crew has stolen a ridiculous amount of antimatter from the larger ship; maybe they have as much as 500 grams. They also swiped anything they thought useful to connect this stolen fuel source to the shuttle. They counted on "disabling the safeties" to make the shuttle accept this fuel source as valid. The engine works for just a few minutes, before the shuttle experiences a series of alarms that causes the automatic systems to get rid of all of the antimatter.

    At this point, I figure that two things would happen: the machinery that holds the antimatter would be ejected and while this is occurring, a stream of matter and antimatter would be "vented" out the engine's exhaust as quickly as possible. Preferably, the antimatter/matter would not be generating any significant thrust, so as not to subject the crew and shuttle to any g forces during a tricky and dangerous automatic process. The only way I can see for this to happen is to make sure there is not any kind of reaction; lots of "fuel" is simply flying out the back end of the shuttle. I was afraid that using magnetic fields to manipulate the antimatter for the rocket would cause unused fuel to loop back to the shuttle.
    Solfe

    -----------------------------------------------------------------------------------
    "Triangles are my favorite shape
    "Three points where two lines meet"
    Tessellate, Alt-J

  11. #11
    Quote Originally Posted by Solfe View Post
    I am writing a story where the characters attempt to put too much matter and antimatter fuel on their shuttle and it wrecks their engine in a scary and annoying way.
    I can't really imagine a scenario in which you could destroy an engine in a non-annoying way.
    As above, so below

  12. #12
    Join Date
    Feb 2003
    Location
    Depew, NY
    Posts
    6,525
    Well, this engine is perverse.

    In destroying itself, it is causing the shuttle to turn in ways that could sweep the other ship with it debris, it isn't giving them thrust when they need it and it is sending out a trail of stuff that basically says "Shoot me or come and get me." On top of that, the heroes are pretty convinced that they did everything they could to prevent any of this from happening.
    Solfe

    -----------------------------------------------------------------------------------
    "Triangles are my favorite shape
    "Three points where two lines meet"
    Tessellate, Alt-J

  13. #13
    Join Date
    Feb 2005
    Posts
    8,018
    Quote Originally Posted by DoggerDan View Post
    But if these identical pairs peacefully co-exist, what's the point?.
    The idea is to keep the identical pairs peacefully contained, but to enter some instability in such a way as to get the antimatter to break free and react with, say, fission products if possible.

Similar Threads

  1. Replies: 3
    Last Post: 2012-May-28, 07:14 PM
  2. the dance of X-rays and Gamma rays together
    By trinitree88 in forum Astronomy
    Replies: 0
    Last Post: 2009-Dec-26, 04:37 PM
  3. beyond gamma rays?
    By The_Radiation_Specialist in forum Space/Astronomy Questions and Answers
    Replies: 13
    Last Post: 2005-Dec-31, 08:59 AM
  4. The galaxy in gamma rays
    By ToSeek in forum Astronomy
    Replies: 1
    Last Post: 2005-Oct-11, 02:49 PM
  5. Replies: 3
    Last Post: 2004-Nov-05, 08:53 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
here
The forum is sponsored in-part by: