# Tag Info

4

There was a lot of hype $10$ to $15$ years ago over the hydrogen economy. It was of course rather odd that anyone could take this seriously. How much free hydrogen gas is available? Answer: virtually none. The problem is that you have to either put electrical energy into water to split it into $H_2$ and $O_2$, or if you chemically condition methane $CH_4$ ...

2

Positronium is an exotic species composed of positron and electron. Depending on the allignment of the spins of postron and electron, the total spin of the positron can be zero or 1 (for the ground state for which l=0) and are designated as: ^1S (para-positronium) and ^3S (orto-positronium)

0

We should start by saying that we don't understand the physics that produced a matter-antimatter asymmetry. It seems likely that the asymmetry was around one extra matter particle per billion or ten billion matter-antimatter particles, but this figure is based on general principles rather than any precise calculation. What this means is that if we take a ...

1

Not really. If we were made of antimatter, we would think of matter as antimatter. Antimatter is really the same as matter, just with an opposite charge and opposite lepton/baryon numbers. The laws of physics would be virtually the same. However, if we were made of matter in a universe that was mostly antimatter, we'd have to be very careful not to get ...

2

The electron and positron are two point charges with opposite sign, and classically , as the field lines are an iconal representation of the charge, when the charge becomes zero there will be no electric field lines from the spot where the two point particles overlap. BUT electrons and positrons are quantum mechanical particles and when close enough ...

35

To maintain lepton number as a conserved quantity. Consider, in detail, what's going on in a beta decay (well, I'm going to ignore the nuclear context). The reaction is then $$n \longrightarrow p^+ + e^- + \nu \,,$$ where you should take the symbol $\nu$ to mean some neutrino (without prejudice about matter-type or anti-matter-type for the moment). There ...

10

So there's this funny rule whose provenance I can't recall, but whose essence is: everything that is not forbidden, eventually happens. This rule is particularly fecund in quantum mechanics. If the process you describe is allowed, then every neutron already is a superposition of neutron and antineutron, and the question is just whether the oscillations ...

0

Whatsoever properties of matter or antimatter are related to "charge" at particle level.........are responsible for annihilation phenomena .Now an interesting question could be that if so then how is it possible that two particles neutron and its anti-particle can annihilate each other...? The reason for this is the , fact of composite nature of neutron and ...

1

A neutron has baryon number = 1, while the anti-neutron has baryon number = -1. Physics Guy has much the same here with quarks, that works as well. In the language of CPT the charge operator reverses the charge of the quarks, so the two up quarks with charge $-1/3$ is flipped to $1/3$ and the down quark from $2/3$ to $-2/3$. I gave this question a 1-vote, ...

4

Every particle has (or can have) an antiparticle. Sometimes, it is even his own antiparticle. An antiparticle $D'$ is (easily said) defined as a particle $D$ after a CPT-transformation. CPT-Symmetry is believed to be a fundamental concept of physical nature. A CPT-transformation is a complete changing of observables of a particle. The C stands for ...

0

Somehow, I don't believe the question of "quickly" needs to be applied here. The reason is simple. For a fission bomb, there is a need to maintain confinement in order for the nuclear reaction to continue - as density reduces, the chain reaction can extinguish. On the other hand, for an "antimatter bomb", as the antimatter heats up, it will start to expand; ...

0

What I mean is, suppose we could somehow get a kilogram of antimatter and contain it safely. "contain it safely" is science fiction. There is no way to keep antimatter in a matter environment safely except by the use of electric and magnetic fields, suspended in them . Even suppose one can create ( another science fiction scenario which I will not ...

1

The obvious answer, to my mind, would be to build an antimatter bomb like a fission bomb. You have a shell of matter (probably the containment unit) around the antimatter which is crushed by some kind of explosive, perhaps a nuclear explosive, creating a rapidly contracting dense shell that can partially overcome the centrifugal tendencies introduced by the ...

0

Likely the dominant process for the positron in the lead plate is simply Bhabha scattering. This is no surprise. We must consider the lab energy of the positron. At center-of-momentum energies less than twice the muon rest mass, the electron and positron annihilation is limited primarily to radiation of multiple photons. At energies above the eV scale, ...

1

As Jon said in the comments, the mean free path before the electron-positron annihilation is longer than 6 millimeters, or at least not much shorter, and it's simply hard for them to annihilate. Most of the space is empty, the electron and positron are pointlike particles, and they're unlikely to hit each other. The mean free path that indicates the "...

0

Books tell us that electricity is constituted only by electrons. But in reality protons also cause electricity. In some materials like conductors this is an exception as protons are fixed at their places and are too heavy to move. So basically electricity is a flow of charge which could be positive or negative.

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