Exploring Positronium: Lifetime, Ionization Energy, and Self-Annihilation

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In summary, the lifetime of Positronium is 142 ns and its ionization energy is 6.8 eV. It undergoes self-annihilation, producing high-energy photons. Hydrogen, on the other hand, has a double ionization energy of 13.6 eV and has an infinite lifetime because it only has one electron. Positronium and hydrogen do not annihilate each other because they are not antiparticles of each other. Conservation laws such as the total number of electrons and total charge in the universe prevent this kind of annihilation from happening.
  • #1
what_are_electrons
The lifetime of Positronium has been measured to be about 142 ns (Nico et al. 1990), and its' ionization energy is about 6.8 eV. It appears to undergo self-annihilation thereby generating high energy photons. Hydrogen, by comparison, has an IE of 13.6 eV, double that of Positronium, but it does not annihilate itself, and has, in effect, an infinite lifetime. The radii of the two systems are effectively the same.

When we shoot a beam of electrons at a beam of positrons we also get annihilation, but when we shoot a beam of electrons at a beam of protons, we get hydrogen atoms.

I would appreciate any insight on the differences in the these two systems that explains the radical differences in behavior. Thanks in advance!
 
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  • #2
Its not that simple as just things with unlike charge annihiliating each other, its just because positronium has a positron and an electron at its orbit, so they annihilate each other because they are anti-particles of each other. not only because they have opposite charge.

The reason why a hydrogen atom don't get annihilated because

1. Only an electron is around, no positrons here to annihilate the electron as well as itself.

2. Even though, a proton and an electron don't annihilate each other, but the orbiting electron cannot be attracted to the proton and fall down to the bottom of the potential well simply because the uncertainty relation says that it is not possible.

Am I understanding your question correctly here? or is it that you're asking something else?
 
  • #3
Put another way, there are two kinds of matter: "regular" matter, which is composed of the familiar protons, electrons, and neutrons (along with other quark combos and leptons and whatnot), and antimatter. Every "regular" particle has an associated antiparticle, which has the same mass but the opposite charge. The antielectron is the positron, and pretty much all the others are just named anti- plus the regular counterpart (antiprotons, antineutrons, etc.). Well, whenever a particle encounters an antiparticle counterpart (and only that counterpart, nothing else will do), they annihilate one another in a flash of EM radiation, as high energy gamma waves.

Protons and electrons don't annihilate one another simply because they are not antiparticles of one another. Furthermore, the mass of the proton is much, much greater than the mass of an electron, so it doesn't really make sense that the electron could annihilate the proton, does it? On the other hand, the positron is the electron's antiparticle. They have the same mass, but their charges are opposite one another. Therefore, they will annihilate if they run into each other.
 
  • #4
Protons and electrons don't annihilate one another simply because they are not antiparticles of one another. Furthermore, the mass of the proton is much, much greater than the mass of an electron, so it doesn't really make sense that the electron could annihilate the proton, does it? On the other hand, the positron is the electron's antiparticle. They have the same mass, but their charges are opposite one another. Therefore, they will annihilate if they run into each other.

So what prevents part of the proton charge from 'annihilating' all of the electron charge?
 
  • #5
elas said:
So what prevents part of the proton charge from 'annihilating' all of the electron charge?
Nothing "prevents" it, since the electron and the proton can combine to form a neutron. That's not the whole story though. Particle-antiparticle annihilation requires a "perfect match" between the two particles - opposite electric charge is not enough. Electric charge is a locally conserved quantum number, and each fundamental particle carries its own charge. A particle cannot pass that charge onto something else (or have that charge "destroyed" by an opposite charge) while retaining its identity ; the particle itself must be destroyed at the interaction point for that to happen. The creation of neutral bound states (ie hydrogen atom) doesn't count either, since the constituents retain their separate charges. While such a system is neutral "as a whole" (ie when seen from afar), the charge distribution becomes apparent when the system is examined at close range.
 
  • #6
Its like neo in the matrix and what the oracle said, agent smith is his evil twin, everything like neo but just the direct opposite. In the end, both neo and smith were killed (am I right) ? And only smith and neo can kill each other, no other tom dick and harry can do that.
 
  • #7
Okay, so here's a couple more things.

There are some rules called conservation rules that tell us how things work. No one really knows why these things are the way they are, they just haven't seen them being broken yet - and they've looked very very hard. Here's one:

"The total number of (electrons + electron neutrinos) - the total number of (positrons + electron anti-neutrinos) is constant*"

So if you put a proton and an electron together, you have to conserve the number of electrons or electron neutrinos. Which means you have to end up with an electron or an electron neutrino.

Here's another conservation rule.

"The total charge in the universe is constant"

So we have two options: Either we end up with an electron or an electron neutrino. But if we think about the charge involved, for it all to add up we have to have a total charge of 0. Well there is a way we can do that. We could get something like:

e + p -> nu_e + n

or electron + proton -> electron neutino + neutron

Here's a new conservation law, you might have seen it at school:

"The total energy in the universe is constant"

If you know that energy and mass are the same thing, then you can work out the energy on the left hand side:
E = m(electron) + m(proton) = 0.5 + 938.3 = 938.8 units of energy
on the right hand side:
E = m(neutrino) + m(neutron) = 0 + 939.5 = 939.5 units of energy

So this reaction *is* possible, but our particles need to borrow some energy from somewhere. This happens sometimes - it's a special type of radioactive decay.

There are other wild ideas - the electron and proton could turn into a neutrino and a photon, perhaps? But these are all excluded by other laws of physics like the ones above, but ones that I'm not going to detail.

Compare this to the positron and the electron - now we have an electron and a positron. If we have photons at the end, then we get a net number of electrons + positrons of zero. But that's what we started with. Also, the total charge adds to zero - so that's fine. Finally, the annihilation is allowed by energy conservation, as the photons have no mass.

Here's a question for you. When electrons and positrons annihilate, they always annihilate to at least two photons. Why do you think that is?


*This rule, called "lepton number conservation", has in fact been broken - but only in a very specific case called "neutrino oscillations" which I won't delve into here. Try google...
 

What is Positronium?

Positronium is a unique atom-like system consisting of an electron and its antimatter counterpart, the positron. It has the same properties as a hydrogen atom, except that the nucleus is replaced by the positron, which has the same mass as the electron but opposite charge.

How long does Positronium last?

The lifetime of positronium is very short, on the order of a few nanoseconds. This is because the electron and positron are constantly moving and interacting, resulting in their eventual annihilation.

What is the ionization energy of Positronium?

The ionization energy of positronium is the amount of energy required to remove an electron from the system. It is the same as the ionization energy of a hydrogen atom, which is 13.6 electron volts (eV).

How does Positronium self-annihilate?

Positronium self-annihilates when the electron and positron come into close proximity and their opposite charges attract, causing them to collide and release energy in the form of gamma rays.

What are the applications of studying Positronium?

Studying positronium can provide insights into the fundamental forces and interactions of matter. It also has potential applications in fields such as quantum computing and medical imaging. Additionally, positronium can be used as a probe for studying material properties and chemical reactions at the atomic level.

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