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Nuclear Questions  
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Posted (11 years 6 months 5 days 20 hours ago) and read 825 times:

As scientists do in particle accelerators, they somehow get itty-bitty particles to ram into each other at near the speed of light developing intense energy. Recently (decades ago), they were able to create antimatter by ramming isotopes together.

1) Are antimatter reactions fission or fusion? Or is it a long-lost third version of nuclear power?

2) the result of an electron and a positron (positive electron) are 2 gamma rays of energy. how much energy is that exactly and would it be better or worse than modern nuclear technology?


The meaning of life is curiosity; we were put on this planet to explore opportunities.
8 replies: All unread, jump to last
 
User currently offlineBobrayner From United Kingdom, joined Apr 2003, 2227 posts, RR: 6
Reply 1, posted (11 years 6 months 5 days 20 hours ago) and read 807 times:

Are antimatter reactions fission or fusion? Or is it a long-lost third version of nuclear power?

Do you mean events that create antimatter? Or the annihilation of antimatter with conventional matter? Anyway, neither of these can really be described as either fusion or fission.

Antimatter is not, per se, a viable tool in power generation. You get lots of energy from matter/antimatter annihilation, but you'd need to pump in even more energy initially to create the antimatter. It would only be viable if we had some supply of antimatter to hand; but we don't.

the result of an electron and a positron (positive electron) are 2 gamma rays of energy. how much energy is that exactly
Take an electron mass (or two, in this case), and multiply by c². You get about 1.02MeV.

and would it be better or worse than modern nuclear technology?
See above. To compare this to the rest of the power industry you'd need some natural supply of positrons.

Incidentally, comparing the energy released by different interactions won't give us a lot of useful information about the how viable a nuclear power process is; it's like choosing the "best" fossil fuel for power stations solely by comparing combustion temperatures.



Cunning linguist
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 2, posted (11 years 6 months 5 days 19 hours ago) and read 791 times:

"Take an electron mass (or two, in this case), and multiply by c². You get about 1.02MeV."

this is actually where i get confused. according to EM tests (or so stated in my physics book), decaying protons are alpha rays and decaying electrons are beta rays, but decaying neutrons are gamma rays. is this saying that two electron-like masses that annihilate each other somehow produce a massive neutron decay energy blast, something on the order of 928.6MeV?




The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineBobrayner From United Kingdom, joined Apr 2003, 2227 posts, RR: 6
Reply 3, posted (11 years 6 months 5 days 18 hours ago) and read 776 times:

A gamma ray could have any energy in a very wide range. It's just a blob of energy, for our purposes.

A beta particle ("ray"?) is a synonym for an electron.

An alpha particle (idem) is the same as a helium nucleus, IE it's a clump of 2 protons and 2 neutrons.

One electron "weighs" about 0.5MeV. Neutrons and protons both "weigh" around 900MeV. If you annihilate either of these with their antiparticles, you'd get gamma rays of equivalent energies.



Cunning linguist
User currently offlineBobrayner From United Kingdom, joined Apr 2003, 2227 posts, RR: 6
Reply 4, posted (11 years 6 months 5 days 17 hours ago) and read 765 times:

decaying protons are alpha rays

Whether or not protons can decay is a matter of some debate, but in any case you're unlikely to achieve it in the lab. Current experiments show that, if it does decay, it takes at least 10³³ years (on average).

A proton is stable because it's the lightest baryon; for it to decay would violate at least one existing (fairly solid) law of physics... but laws are being updated all the time  Wink/being sarcastic

A mention of "proton decay" might also refer to a nucleus decaying by kicking out one or more of its component protons (IE Ne-18 to O-16). What context is this in?

decaying electrons are beta rays, but decaying neutrons are gamma rays

Electrons are also rather stable (vaguely similar arguments to protons). Any mention of electron decay in a textbook is more likely to be about some larger object decaying by a process that creates an electron.

Neutrons are the only one of the three that are likely to decay; producing a proton, an electron (a beta "ray"), and also an electron antineutrino (which we can forget about for now).

Again, references to "neutron decay" might mean a heavy nucleus trying to stabilise itself by ejecting a neutron.



Cunning linguist
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 5, posted (11 years 6 months 5 days ago) and read 732 times:

Alrighty then Bobrayner, I guess the word 'decay' might not have been appropriate. In any case, those were some good points and corrections, thanks.

Also, if you don't mind, I heard something about antimatter (if ever being used) on the discovery channel once describing that "...a matchbox-sized amount of antimatter would provide more energy than a railroadcar-sized amount of uranium..."

Any guesses on what they could have been refering to?



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineAirways1 From United Kingdom, joined Jul 1999, 560 posts, RR: 0
Reply 6, posted (11 years 6 months 4 days 23 hours ago) and read 729 times:

The point is this: a mass m is equivalent to an energy mc², hence Einstein's equation E=mc².

If you take a load of carbon (coal) and burn it, you would find that the total mass of all the combustion products would be very slightly less than the total mass of the carbon, plus the oxygen that went into burning it. This is a chemical reaction, and this mass defect is very small, so the amount of energy released is correspondingly small.

In the case of uranium, essentially the nucleus splits into two or more smaller particles. The combined mass of these particles is smaller than that of the uranium nucleas, this dispcrepancy again being related to the energy released. This mass difference is a much larger proportion in the case of nuclear reactions, such as the fission of uranium, than in chemical reactions such as the combustion of carbon, and hence the harnessable energy is much greater from a mass of uranium than an equal mass of carbon. Nevertheless, this mass difference as a fraction of the total mass of the fissionable material is still small.

In the case of anti-matter, on the other hand, the entire mass of the anti-matter and the matter which is required to anihilate it goes into energy, and thus the energy yield is much, much higher for an equivalent mass of anti-matter.

airways1


User currently offlineBobrayner From United Kingdom, joined Apr 2003, 2227 posts, RR: 6
Reply 7, posted (11 years 6 months 4 days 19 hours ago) and read 715 times:

Also, if you don't mind, I heard something about antimatter (if ever being used) on the discovery channel once describing that "...a matchbox-sized amount of antimatter would provide more energy than a railroadcar-sized amount of uranium..."

Airways1 - good answer  Smile

A normal nuclear reactor running on uranium will harness a uranium decay process to convert a very small % of the uranium's mass into energy, according to E=mc². The final waste products (a few steps down the decay chain) will weigh very slightly less than the original fuel.

With antimatter, you effectively get 200% (IE the energy equivalent of the antimatter's mass, plus that of the matter it annihilates with). There should be no waste product in the ordinary sense; it's all been converted into gamma rays (&c), which can then be used to heat liquids that drive turbines, like in most other power stations.

So, yes, you could get as much power from a matchbox of antimatter as you could from (say) a railroad car of uranium. That's very true.

The problem is that we have uranium lying around, but not antimatter. If you wanted to create the antimatter first, then (allowing for inefficiencies) you'd need several railroad cars full of uranium to power an antimatter-producing process for long enough to get the matchbox full.



Cunning linguist
User currently offlineJwenting From Netherlands, joined Apr 2001, 10213 posts, RR: 18
Reply 8, posted (11 years 6 months 4 days 17 hours ago) and read 706 times:

a proton can not decay... It might fall apart into quarks but it cannot decay radioactively.
Certainly it cannot decay into something smaller emitting alpha particles for alpha particles are made up of protons and neutrons (which are heavier than protons).

What proton decay actually means is that a material can decay into another material by emitting protons (rather than other particles like alpha (He4 cores) or beta (electron) particles.
In that it's equivalent to neutron emission (except the electrical state of the leftover particle won't be neutral unless there is a simultaneous beta emission as well).

A matter-antimatter reaction is neither fission nor fusion. It's an annihilation reaction in which the matter and antimatter are combined with the only result being energy (plus what matter or anti-matter is left after the reaction for lack of material to react with of course).

Another problem not yet mentioned about antimatter reactors is the extreme reactivity of the material.
You'd need such amounts of energy to contain the antimatter in a way in which it will have no contact with normal matter that you'd loose whatever energy it produces right there.
If the antimatter were ever to touch the wall of the containment vessel it would instantaneously react with the wall in a massive reaction, effectively causing a large pulse of energy combined with a large hole in the containment vessel (and whatever lay under it).
In that, it's similar (but worse) than nuclear fusion. A fusion reaction can be stopped by cooling the plasma after which the containment field can be shut down. An antimatter reactor cannot be stopped, ever, until any and all antimatter contained within the field has been spent.



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