Tag Info

3

When an electron-positron pair approach they can form positronium, a very low mass and very temporary hydrogen-like system. It comes in two forms, ortho- and para-, depending on the relative orientation of the spins. With para-positronium they have opposite orientations; this is the lowest energy or ground state for positronium. The excited states can, and ...

3

The symmetries that you're missing are conservation of baryon number $B$ and lepton number $L$. We strongly suspect that baryon number is not an exact symmetry, because the universe appears to contain very many baryons and very few antibaryons. Actually, a better metric for the baryon asymmetry of the universe is to compare the baryon density to the density ...

3

The electron is the lightest lepton and the proton is the lightest baryon, so it's hard to see what reaction could occur without violating lepton number or baryon number. I suppose if proton decay (to a pion and positron) occurs then there could be a reaction to give a pion and two photons.

3

The question is based on a misunderstanding. We will do the work in the center of mass frame of the incident particles, and assume a two photon final-state (in practice it also occurs to a thre-photon state). We have a total incident a four-vector of $(\gamma m_e c^2,\vec{0})$ (this simple form is why I chose to work in the CoM frame). The two photons ...

3

Let us start with the wiki article: The singlet state with antiparallel spins (S = 0, Ms = 0) is known as para-positronium (p-Ps) and denoted 1S0. It has a mean lifetime of 125 picoseconds and decays preferentially into two gamma quanta with energy of 511 keV each (in the center of mass frame). Detection of these photons allows for the reconstruction of ...

2

Jezstarski is mostly correct, The para-positronium (p-PS) state ends up being the main mode of annihilation of positronium (PS). Positrons can annihilate in at least eight different ways but once ortho-positronium (o-PS) forms in a void/vacuum, it has additional time to undergo another mode of annihilation. P-PS annihilates in under 125 picoseconds. O-PS ...

2

My 2 cents: If only two gamma rays are produced with each of their energy equaling the rest energy of either e- or e+ (which is 511keV) then, it could possibly mean that there is no net linear momentum, which possibly means that this e+ and e- pair are very very close to each other and after collision, the gamma rays are emitted as per the law of ...

1

You can start with the electromagnetic spectrum: https://en.wikipedia.org/wiki/Electromagnetic_spectrum And particle decay rates: https://en.wikipedia.org/wiki/Particle_decay and follow the references.

1

Your proposal will work as long as mass and charge enter into the expression in a ratio 1:-2. Find an expression with a different ratio (like electric potential, or radiated power ...) and you're sunk. The fine structure constant $$\alpha = \frac{e^2}{\hbar c} \tag{Gaussian units}$$ is an example of such an expression and controls the fine structure of ...

1

Let us see how the notion of the "electron cloud" enters the calculations. In the first Born approximation, the elastic scattering is determined with the atomic form-factor $F$ containing the reduced mass in the wave function and the "electron coordinate" in the exponential: $$d\sigma\propto|Zf(\mathbf{q})-F(\mathbf{q})|^2,\qquad (1)$$ F(\mathbf{q})=\int ...

1

Well, the details are important. From the abstract in your link of the paper we see that: 1) it is a publication from 1978 2) it calculates rates for positronium annihilation in the very high magnetic fields found in astrophysical situations, 10^12 Gauss It explicitly states that the momentum contribution comes from the magnetic field. In the relevant ...

1

Positronium is a quantum mechanical entity. It is a bound state in the potential create between two elementary "particles". Even though the wiki article draws a nice picture of he electron and positron orbiting about their center of mass this is a representation as if they are classical particles . They are not. The electron and positron are not in orbits, ...

1

I'm afraid the responses so far are either misleading or do not answer the question. In fact in a dense medium a positron when it forms the longer lived ortho-positronium can "pick-up" an electron from an adjacent atom and then decay into 2 x 511 keV photons long before the 3-photon ortho-positronium state would have decayed. Look up "pick-up effect".

1

I have only an amateurs understanding, but it seems to me that a strong vacuum and EM fields are needed to trap positrons (see Penning Trap on wikipedia). I have wondered if ionizing the remaining scant air within a vacuum tube would improve the preservation of positrons in a Penning Trap. My reasoning is that positively charged gas molecules would repel ...

Only top voted, non community-wiki answers of a minimum length are eligible