proton-antineutron interaction

[acrosome]

Hey,

Way back in this thread I contemplated make-on-demand antimatter via Visser wormholes, and picked the brains of people much smarter than myself. Among other things I learned that electron-positron obliteration is a somewhat smaller scale of blazing radioactive death than is proton-antiproton obliteration.

But I recently learned that proton-antineutron obliteration is a thing, and I know nothing about it. I can't find much (acrosome-understandable) information on the resulting particles and how they behave. It's easy to miss stuff such as, for instance, uncharged pions rapidly decaying into energetic gamma rays.

Basically, I'm pretty sure it's a pipe dream, but I'm looking for a TL10 torchship power source that is not blazing radioactive death (to some tolerable degree).

So who can tell me about proton-antineutron reactions?

[Anthony]

You get the same products as you'd get from the antineutron decaying, and then the antiproton annihilating -- so you get an electron and an electron antineutrino, plus what you normally expect.

[acrosome]

What do you "normally expect"? Other than craptons of heat. More pions? Are the charged or neutral? Etc.

Also, it isn't an antiproton. It's a proton. Apparently a proton and an antineutron can obliterate one another.

[Anthony]

Originally Posted by acrosome

What do you "normally expect"? Other than craptons of heat. More pions? Are the charged or neutral? Etc.

Also, it isn't an antiproton. It's a proton. Apparently a proton and an antineutrino can obliterate one another.

Proton and antineutron, not antineutrino. You have to keep charge, baryon number, and lepton number balanced. A proton has a charge of +1 and a baryon number of +1, an antineutron has a baryon number of -1, so you need to have final products with a charge of +1 that is less massive than a proton, which means a positron or anti-muon. Those have a lepton number of -1, so we need to balance it out with a neutrino (I was getting the numbers wrong before).

The total energy of the proton-antineutron is 1876 MeV, the total of a positron and a neutrino is 0.511 MeV, so the remaining energy will be used for production of particles, most commonly pions, pair production of electron-positron pairs, and gamma rays.

[acrosome]

Originally Posted by Anthony

Proton and antineutron, not antineutrino.

Spellchecker bit me... I think?

Originally Posted by Anthony

You have to keep charge, baryon number, and lepton number balanced. A proton has a charge of +1 and a baryon number of +1, an antineutron has a baryon number of -1, so you need to have final products with a charge of +1 that is less massive than a proton, which means a positron or anti-muon. Those have a lepton number of -1, so we need to balance it out with a neutrino (I was getting the numbers wrong before).

The total energy of the proton-antineutron is 1876 MeV, the total of a positron and a neutrino is 0.511 MeV, so the remaining energy will be used for production of particles, most commonly pions, pair production of electron-positron pairs, and gamma rays.

Are the pions charged? Because that matters when you're trying to use them for thrust. And how energetic are the gamma rays?

I was hoping that this interaction had been studied and there was a paper out there somewhere describing it, but my google-fu is failing me.

[AlexanderHowl]

Around a sixth of the pions should be useable for thrust in a realistic drives, meaning that only around a tenth of the total energy will be useable for thrust. The gamma rays should be around 100 MeV if I remember correctly.

[dataweaver]

Proton is two up-quarks and a down quark; anti-neutron is one anti-up and two anti-downs. Combine them and you get the annihilation of an up and an anti-up, the annihilation of a down and an anti-down, and left-overs being one up-quark and one anti-down quark. This results in a pion, which has the same charge as a proton.

[Anthony]

Note that, if you don't need near-C exhaust, antiproton collisions with nuclei tend to result in the pions being captured by other particles in the nucleus, blowing the nucleus apart (and, other than different remaining charge, the same for antineutrons). This tends to give you free neutrons, which is not ideal, but probably no worse than the high energy gamma rays you get otherwise, and you can potentially absorb them for antimatter-catalyzed microfission, which has been studied as a drive.

[acrosome]

Originally Posted by dataweaver

Proton is two up-quarks and a down quark; anti-neutron is one anti-up and two anti-downs. Combine them and you get the annihilation of an up and an anti-up, the annihilation of a down and an anti-down, and left-overs being one up-quark and one anti-down quark. This results in a pion, which has the same charge as a proton.

Whoa, wait- so all you get is a charged pion and craptons of energy? So, for instance, the pion could be manipulated with a magnetic field to simply get launched out the back? No radioactive death? What do the pions decay into, and how fast?

My innate skepticism makes me suspicious regarding the viability of this a possible solution. Also, it conflicts with what Anthony said- he mentioned gamma rays, etc. Everything else he mentioned sounded manageable, with the exception of muons, about which I know startlingly little.

Originally Posted by Anthony

Note that, if you don't need near-C exhaust, antiproton collisions with nuclei tend to result in the pions being captured by other particles in the nucleus, blowing the nucleus apart (and, other than different remaining charge, the same for antineutrons). This tends to give you free neutrons, which is not ideal, but probably no worse than the high energy gamma rays you get otherwise, and you can potentially absorb them for antimatter-catalyzed microfission, which has been studied as a drive.

Well, I do want torchship-equivalent performance, which I'm pretty certain means ludicrous exhaust velocities. Otherwise, this sounds intriguing and I wish to subscribe to your newsletter.

[Anthony]

Originally Posted by acrosome

Whoa, wait- so all you get is a charged pion and craptons of energy?

A pion has a mass of 139 MeV, so the remaining 1747 MeV produces whatever particles it can with the leftover energy.