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Colt
2003-Feb-22, 09:06 AM
I know that it takes a long time for us to create even small amounts of anti-matter right now but we can still create it. What is stopping us from building an anti-matter fueled ship to mars? AM containment? Propulsion unit? I have never really heard a good reason as to what is stopping us. Well, just wanted to start this thread before I go to sleep so I can check it in the morning. Night. -Colt

David Hall
2003-Feb-22, 09:16 AM
By small amounts, we're talking on the order of a few protons here and there. Not even enough to give a good bang.

And if we could create enough, we still don't know how to harness it effectively or use it for propulsion.

liglats
2003-Feb-22, 10:27 AM
Somewhere I have a copy of "The Physics of Star Trek", where the author looks into the probability of anti-matter propulsion. (I'm moving house and it is in a box somewhere...)

Even without looking at Warp Drive, we would have to supply a ridiculously large amount of power to some unbelievably large particle accelarators to get even small amounts of anti-matter. If anyone has a handy copy of the book, a quote here would be good.

John Kierein
2003-Feb-22, 12:12 PM
There may be easier ways to get anti-matter. There are some normal matter elements that naturally radiate anti-matter in the form of anti-electrons, or positrons. This is sometimes called negative beta decay. I think there is an isotope of potassium that does this. It's a problem of capturing the anti-matter and containing it in a magnetic field so it doesn't interact with matter before it's used as propellant.

But I have never felt that matter anti-matter annihilation would make a good propellant. This is because that the huge amount of energy released is in the form of gamma rays. Gamma rays penetrate things better than x-rays and are ionizing radiations that produce damage to humans and robotic electronics. It takes lots of shielding to capture this energy once released and convert it to useful heat and thermodynamically useful propellant. Otherwise it just escapes through the combustion chamber and goes out into space in all directions.

Glom
2003-Feb-22, 12:16 PM
On 2003-02-22 07:12, John Kierein wrote:
There are some normal matter elements that naturally radiate anti-matter in the form of anti-electrons, or positrons. This is sometimes called negative beta decay.


I thought Beta-negative decay was when a neutron turns into a proton and throws out an electron, while Beta-positive decay was when a proton turns into a neutron and throws out a positron.

John Kierein
2003-Feb-22, 12:52 PM
You are right. The charge of a positron is positive and an electron is negative. So a negative electron charge is positive. I thought they used a confusing notation, but not so. http://www.npp.hu/mukodes/beta-e.htm
I just had thought that since beta radiation was normally negative charge, so an anti-matter counterpart to beta was called a negative beta which would have a positive charge. Not true.
The point is that there are natural sources of antimatter without having to resort to accelerators if you can contain it. The should call electrons negatrons, but it has never caught on.

Sodium naturally radiates positrons.

<font size=-1>[ This Message was edited by: John Kierein on 2003-02-22 08:02 ]</font>

roidspop
2003-Feb-23, 02:08 AM
Speaking of gamma rays, there was this article about using an isotope of hafnium as a source of energy for a UAV. It could also be used for space propulsion, but the shielding issue would be tough to get around.

http://www.newscientist.com/news/news.jsp?id=ns99993406

John Kierein
2003-Feb-23, 09:54 AM
Fly it on Mars! Use it as a power source for Europa. Use it for unmanned space exploration.

<font size=-1>[ This Message was edited by: John Kierein on 2003-02-23 04:55 ]</font>

daver
2003-Feb-24, 06:57 PM
On 2003-02-22 04:06, Colt wrote:
I know that it takes a long time for us to create even small amounts of anti-matter right now but we can still create it. What is stopping us from building an anti-matter fueled ship to mars? AM containment? Propulsion unit? I have never really heard a good reason as to what is stopping us. Well, just wanted to start this thread before I go to sleep so I can check it in the morning. Night. -Colt



There was a book by Robert Forward called MIRROR MATTER that went into this in some detail. One of his contentions was that currently anti-matter production was way, way, suboptimal. With a bit of research it might be possible to make the process much more efficient. Anyway, we're a long ways from there right now.

dgavin
2003-Feb-25, 03:56 AM
Actualy Nasa has built a -portable- antiproton trap, called the HiPAT.

Here's a little information on it.

http://std.msfc.nasa.gov/sciresearch/antimatterpropulsiontechsummary.pdf

chivis
2003-Feb-25, 05:34 AM
Just me thinking outside the box again but....

Even if you could use this energy as a propellant, you couldn¡¦t possibly travel far enough, fast enough to make space travel even remotely conceivable. Other then exploring the Kuiper Belt and The Oort Cloud, you couldn¡¦t possibly travel to other star systems with propulsion alone.

There has got to be another way! I think we need to understand the time/space relationship and travel through both simultaneously. Otherwise, isn¡¦t it just a waste of time?

But maybe I¡¦m thinking too far ahead. I guess visiting Jupiter would be nice too ƒº

~Chivis

logicboy
2003-Feb-25, 04:23 PM
Here is a cool site about antimatter propulsion.

Wishfull Thinking (http://ffden-2.phys.uaf.edu/213.web.stuff/Scott%20Kircher/plasmacore.html)

Reacher
2003-Mar-05, 06:09 PM
I am still a little unsure of this whole anti-matter thing. I know what it is(i think)and i beleive that this is how it works: AM comes into contact with matter, bang. but does it have to be the same type? e.g anti-hydrogen, hydrogen? can you get "anti-hydrogen"? and after the bang, wouldnt the remnants react, causing a never-ending bang?

David Hall
2003-Mar-06, 04:23 PM
Well, I know we can get anti-hydrogen, because I remember reading about how it's just recently been done in the lab. Basically, all atomic reactions are the same as with matter, just reversed in polarity.

I'm not sure about restrictions in matter-antimatter interactions though, since I'm not a physicist. But here's my guess. Positrons would be attracted to electrons due to their opposite charges, as would protons/antiprotons. Protons would repel positrons because they have the same charge.

Here's a question, are neutrons the same in both matter and antimatter? I honestly don't know.

Anyway, when two atoms meet, the proton-antiproton and electron-positron pairs would interact as above and annihilate each other to the limit of the smaller mass. The released energy would probably be enough to shatter what's left and sling out a large number of subatomic particles.

Someone let me know how I did here. /phpBB/images/smiles/icon_smile.gif

daver
2003-Mar-06, 07:28 PM
On 2003-03-06 11:23, David Hall wrote:
Well, I know we can get anti-hydrogen, because I remember reading about how it's just recently been done in the lab. Basically, all atomic reactions are the same as with matter, just reversed in polarity.

I'm not sure about restrictions in matter-antimatter interactions though, since I'm not a physicist. But here's my guess. Positrons would be attracted to electrons due to their opposite charges, as would protons/antiprotons. Protons would repel positrons because they have the same charge.

Here's a question, are neutrons the same in both matter and antimatter? I honestly don't know.

Anyway, when two atoms meet, the proton-antiproton and electron-positron pairs would interact as above and annihilate each other to the limit of the smaller mass. The released energy would probably be enough to shatter what's left and sling out a large number of subatomic particles.

Someone let me know how I did here. /phpBB/images/smiles/icon_smile.gif



I was hoping someone else would post so i wouldn't have to embarass myself in public, but here goes.

Let's answer the simple one first. Neutrons and anti-neutrons are different. Neutrons are made up of quarks, antineutrons of antiquarks.

Let's say you drop a small piece of antimatter in a cloud of matter. The positrons and the electons annihilate each other pretty quickly, producing two gamma rays per collision (there's enough energy involved that some mesons might be created as well, which would in turn decay, so your gamma ray output may have more than one peak).

The protons and neutrons are a bit messier (and i'm less sure about the reactions). My guess is that it would take longer (but on a human scale, still virtually instantaneous) for the antiprotons and antineutrons to start reacting--an anti-proton (or if you're using more complex anti-atoms than anti-hydrogen, an anti-ion) would have to replace an electron in a regular atom. Eventually a baryon and an anti-baryon would come into close enough contact that the quarks and anti-quarks interact, producing three mesons.

It shouldn't matter if the reaction was between a proton and an anti-proton or a proton and an anti-neutron or what have you--they still annihilate each other (well, it does make some difference. I think that if a proton collides with an anti-proton, that none of the resulting mesons will be charged, whereas neutron vs anti-neutron may result in some charged mesons, and proton/anti-neutron must result in some charged mesons. If your drive system relies on the mesons having charges, you'll want to make sure that there are some neutrons or anti-neutrons involved in the annihlation).

The mesons go speeding off, possibly spitting of positrons and electrons as they decay (or maybe higher-energy leptons). Also neutrinos and antineutrinos. Eventually all the antimatter reacts with normal matter, and you're left with a bunch of neutrinos and gamma rays.

OK, that should be enough impetus to prompt someone to post what really happens.