What is Positron: Definition and 115 Discussions

The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1 e, a spin of 1/2 (the same as the electron), and has the same mass as an electron. When a positron collides with an electron, annihilation occurs. If this collision occurs at low energies, it results in the production of two or more photons.
Positrons can be created by positron emission radioactive decay (through weak interactions), or by pair production from a sufficiently energetic photon which is interacting with an atom in a material.

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  1. P

    Positron Generator: Create Anti-Particles & 100% E=MC2?

    if you have a beam of high energy electrons ( enough energy to create positrons) that hit plate in a vacuum that was positively charged could you produce anit particles without the particels annihilating it self (hence the vacuum) and have the positivly charge particles suspended in a magnetic...
  2. S

    Can photon capture give electron and positron opposite charge

    Is it possible, in theory, that the physical entity electron e(-) and its charged opposite positron e(+) both obtained their respective electric charges by simultaneous capture, by a more fundamental quantum entity (call it FQE), of a quantum of photon with zero rest mass having equal amounts of...
  3. S

    Natural positron emitters

    There are 3 long lived (over 10^9 years) isotopes which may capture electrons and have actually been observed to undergo single beta transmutation. Interestingly, all these 3 ALSO can undergo beta decay AND positron emission. Potassium 40 has a branching ratio of about 1000 electron...
  4. F

    Electron Capture vs Positron Emision

    I'm having some slight confusion over what seems to be a violation of conservation of mass: Both electrons and positrons have positive mass, so now consider an atom that undergoes a beta decay, and so has it's mass changed by the difference in mass between a proton and a neutron. How does it...
  5. P

    Build Positron Accelerator | Safety Tips & Experiments

    Hello all, My son and I have been doing experiments with a simple cloud chamber and I am curious what type of accelerator I might be able to build that would be strong enough to make positrons? Then I will use a magnet with the cloud chamber to show him that they are charged differently. A...
  6. P

    Are the Electron & Positron Created from a Photon Scattered at the Same Angles?

    Hello. Firstly, I hope this is the right sub-forum for this question. Here's a quick question that I have. After an electron-positron pair production, do the angles that the paths of the electron and the positron make with the original path of the photon have to be equal? Another way to ask...
  7. T

    Photon decay into Electron and Positron

    Homework Statement Show that the energy momentum conservation forbids the reaction (gamma)-> positron + electron, Gamma is a photon, which is chargeless and massless Homework Equations E(photon)=hf p(photon)=hf/c Conservation of Energy Conservation of Momentum 4-momentum The Attempt at a...
  8. S

    Helicity of the positron in zero mass limit

    Hi... I read somewhere that positron, in the massless, limit will have the same helicity as the antineutrino. This must be because they are in the same SU(2) doublet. So helicity operator must commute with the SU(2) generators. Please confirm.
  9. I

    Feynman diagram of electron and positron annihilation

    Hi all, I am learning Feynman diagrams, and I have a quick question: in diagrams such as the one for electron-positron annihilation (see http://en.wikipedia.org/wiki/Feynman_diagram#Electron-positron_annihilation_example) why is it that the line "in the middle" is that of an...
  10. A

    Application of Coulomb's law to positron velocities

    I have an idea in which I need to manipulate a positron using an electrical field. However, in order for the problem to work, I need to make sure that the positron's kinetic energy is under 511 keV. to do this, I used Coulomb's law (F=\frac{kQ1Q2}{r^2}) to obtain the force. Because F = ma, I...
  11. E

    Annihilation of electron and positron

    Homework Statement A positron with kinetic energy 2.2MeV collides with an electron at rest, and annihilate each other. a. Calculate the average energy of the two gamma photons produced as a result of annihilation Homework Equations The Attempt at a Solution I would infact...
  12. O

    Positron emission (Beta + decay)

    Why does β+ decay occur? If protons are stable and all baryons eventually decay to protons, then how is it that protons can 'decay' to a neutron? What causes this to happen? (I assume it isn't as frequent as β- decay, or up and down quarks would be coming and going constantly, and we'd be...
  13. G

    Electron positron system

    Homework Statement Hamiltonian for an electron positron system in a uniform magnetic field B (in the z direction) ## \hat{H} = AS^{(-)} \cdot S^{(+)} +\frac{eB}{mc} (S_z^{(-)} +S_z^{(+)} )## ##A \in \Re ## We have a spin ket given by ## |\psi \rangle = | \uparrow \rangle^{(+)} | \uparrow...
  14. B

    Electron positron pair density in charge renormalization

    I am trying to find out the density of electron positron pairs around a bare electron charge. In most texts, I saw that the treatment relates to the observed charge vs. the bare charge. I wanted to know if there is a formula that describes the density of electron positron pairs that surround...
  15. S

    I recently saw in my physics textbook a diagram of a positron and a

    i recently saw in my physics textbook a diagram of a positron and a electron being created in pair production. The diagram showed that as soon they where created, they moved in opposite directions and then they spiralled inwards a bit. Now i think the reason why they move in opposite directions...
  16. B

    Is charge conserved in positron emission?

    Consider the reaction: ^{39}_{20}Ca \rightarrow ^{39}_{19}K + \beta^{+} I understand that a proton in the Calcium nucleus is being split into a neutron, which stays in the nucleus, and a positron, which gets ejected. But if you look at the equation above, charge is not conserved. The only...
  17. L

    Can Protons or Positrons Flow as a Current?

    Instead of electrical current could there ever be a situation where protons or positrons are made to flow as a current?
  18. K

    Energy level of hydrogen atom - with the electron replaced by a positron

    Energy level of hydrogen atom -- with the electron replaced by a positron The energy level of a hydrogen atom is given by (without fine structure consideration) Eh = -13.6 eV / n^2 Suppose -- if the electron is replaced by a positron, what would happen to this energy level? The resulting...
  19. J

    Positron Helix magnetic field, find pitch and radius

    Homework Statement A uniform magnetic field of magnitude 0.137 T is directed along the positive x axis. A positron moving at a speed of 5.40 106 m/s enters the field along a direction that makes an angle of θ = 85.0° with the x-axis (see figure below). The motion of the particle is expected...
  20. S

    Industrial grade positron formation

    Is there any way to economically produce positrons using particle accelerators or any other method?
  21. P

    Feynmann diagram - positron representation

    Hello, this might be a basic question. In feynman diagram's we represent the positron as traveling backwards in time. Is that correct ? How do we interpret this ?
  22. D

    What is the mass and lifetime of the φ meson?

    An electron and a positron are collided head on such that all their energy is used to produce a φmeson. The number of observed φ mesons is found to be inversely proportional to (E−E0)+Γ2/4. where E is the total centre of mass collision energy, E0=1019 MeV and Γ=4.26MeV What is the mass and...
  23. B

    Particle Accelerator Problem, proton -> electron positron

    Particle Accelerator Problem, proton --> electron positron He guys, I could use some help on this problem. [PLAIN]http://img31.imageshack.us/img31/2039/physhw.jpg I got the energy of the photons: E = 2hc/lambda Energy of the electron and positron I believe are: E =...
  24. B

    Photon decay into positron and electron

    Homework Statement Why can't a 3.141 MeV photon decay spontaneously into an electron and positron, each with rest mass energy .511 MeV?Homework Equations Conservation of Momentum and Energy E=\sqrt{m^2c^4+p^2c^2} E_\gamma=pc The Attempt at a Solution 3.141=\sqrt{(.511)^2+p^2c^2}...
  25. J

    Is it possible to create a Positron - Electron cooper pair?

    Hello, Would it be possible for an electron and positron to form a cooper pair if an electron is brought into the neighborhood of the positron who is anchored in a penning trap (or in some other fashion)? If normal cooper pairs form by using the the attractive force of the lattice...
  26. T

    Annihilation of Electron by Positron to Produce at least 2 Gamma Rays

    Homework Statement The problem is listed as follows: Show that conservation of energy and momentum require at least two gamma rays to e emitted in the annihilation of an electron by a positron. Homework Equations p(initial) = p(final) E(initial) = E(final) Total rest mass = 1.0218...
  27. DuckAmuck

    How do photons split into electrons and positrons?

    I'm confused about how photons are able to split into electrons and positrons. Learning about four dimensional vectors, but it's still not clear how this happens. The photon will have a vector of P=(E,p), where p^2=E^2, so P^2=0, since photons don't have mass. It must be that P = P1 + P2...
  28. J

    Positron - electron annihilation.

    Here is an excerpt from my textbook: "The mass of a Z boson is about 90 Gev. By selecting the energy of the electron and positron beams in the LEP collider to be 45 Gev each, a high rate was achieved for the production of neutrino-antineutrino pairs in the process. The experiment shows that...
  29. C

    Positron Emission: Exploring the Science Behind It

    I've been wondering about positron emission. If a neutron has more mass than a proton, how can a proton turn into a neutron by releasing a particle with mass? [PLAIN]http://img37.imageshack.us/img37/654/positronemission.gif (source:http://en.wikipedia.org/wiki/Positron_emission) Doesn't this...
  30. R

    Electron - positron annihilation

    Apologies if this question is already covered. I searched, but couldn't get info from pf. when electron-positron annihilation happens..what is emitted ? as per wiki, its gamma rays but on cern website i read that muon pairs(muon and anti muons) are emitted. which one is correct ?
  31. F

    Does a positron absorb a Photon?

    Does a positron absorb a photon like an electron does? When an electron absorbs a photon it increases in energy, but does that happen for a positron? Thanks.
  32. K

    Electron and Positron Annihilation

    Homework Statement An electron traveling at 0.8c annihilates with a positron that is at rest, producing two photons. One of the produced photons travels in the direction of the electron. Determine the energy of each of the photons.Homework Equations p_{photon} = \frac{E}{c} P_{electron} =...
  33. S

    Positron lifetime calculations on ABINIT

    Dear memebers of this community: Although I am newbie in using ABINIT I though I understood the basic features of it until I confront myself to the example of positron calculations (/abinitx.x.x/tests/v4/Input/t95.in and /abinitx.x.x/tests/v4/Input/t96.in ). I found that for running that test...
  34. tom.stoer

    Neutrino pair creation in electron positron scattering

    Hello, does anybody know how to compare (at tree level) the two reactions e^- + e^+ \to \gamma^\ast \to e^- + e^+ and e^- + e^+ \to Z^\ast \to \nu + \bar{\nu} \;\;\; \text{and} \;\;\; e^- + e^+ \to W^\ast \to \nu_e + \bar{\nu}_e The first process is the so-called Bhabha...
  35. L

    Another q on electron positron collisons

    Another q on electron positron collisons :) I asked earlier about why spin-0 bottomonium mesons aren't created directly with electron positron collisions. So I found out that when an electron and positron collides, it may make a virtual photon, and the virtual photon turns into a spin-1...
  36. D

    Electron and Positron system

    Homework Statement The system consists of an electron and a positron, which are rotating around each other. Using Bohr's theory of the hydrogen atom, what are possible orbits' radius (from the system mass center) and possible energy equation. Homework Equations The Attempt at a...
  37. A

    Calculating Total Energy of Positron and Electron in Quantum Physics Problem

    Homework Statement Hi I am new to this forum and offering quantum physics at A level. Can anybody help with the following problem: The rest energy of an electron is 0.511MeV. A positron created in a cloud chamber has 0.158MeV of kinetic energy. It collides with an electron at rest...
  38. I

    What is the orbital frequency of an electron and positron 2.00nm apart?

    A positron is an elementary particle identical to an electron except that its charge is . An electron and a positron can rotate about their center of mass as if they were a dumbbell connected by a massless rod. What is the orbital frequency for an electron and a positron 2.00nm apart? My...
  39. Q

    Electron - Positron Annihiliation

    I know that positrons are produced by beta + decay and I know that they are antimatter. My question now comes to what happens when the collide. I know that should be complete annihiliation and the most likely outcome is the production of two or more gamma rays. My question comes when trying...
  40. D

    What's the difference between an electron hole and a positron?

    Qualitatively speaking, an 'electron hole' and a positron sound quite similar. Are they they same? If they are, why are different terms used and what is the utility of that, and if they aren't the same, am I completely wrong in assuming that they are in some way analogous? What kind of tree am I...
  41. S

    Positron neutrino=electron antineutrino

    Hi everybody, Basically, the title of this thread says it all. My question is: Since all particles have an antiparticle and the positron is the electron's antiparticle, does that mean the positron-neutrino is the same as the electron-antineutrino? If not, is there such a thing as a...
  42. R

    Why is the Decay of Neutral Pion to Electron Positron Pair Forbidden?

    Why the decay of neutral pion to electron positon pair is forbidden?
  43. S

    Exploring Lepton Annihilation and Hadron Formation in the Standard Model

    Imagine you have electron and positron (leptons) falling towards each other. The interaction between these two is electromagnetic at long distances. It is well established that this reaction eventually leads to annihilation of these two particles. Now consider electron and proton(hadron) falling...
  44. B

    Electron-Positron Attraction: How Do These Particles Interact?

    I have been doing some thinking and I can't find the answer to my question anywhere, so I was wondering if someone else knew. My question is simply this: Do electrons and positrons attract each other electromagnetically, or do the antimatter properties of the positron alter the interaction in...
  45. F

    A positron moving from a Charged Plate to Another

    A positron moving from a Charged Plate to Another [SOLVED] Can you solve the question a and b and explain it to me ? What i know ? ( I'm not sure though ); Kinetic Work = Kinetic Energy = 1/2 m . v^2 Electrical Work = Electrical Energy = q.V So at the begin, the positron isn't moving...
  46. E

    Electron and positron length contraction q.

    Homework Statement In the stanford linear accelerator, electrons and positrons are fired at each other at 50Gev. In the lab, each electron and positron beam is 1cm long. (a) how long is each bundle in its frame? (b) what is the proper length of the accelerator for a bundle to have both its...
  47. J

    Electron positron helicities and gamma-5

    Hi all, I've read that in the QED process e^+e^- \to \mu^+\mu^-, terms in the scattering amplitude coming from electrons and muons of the same helicity do not contribute. I don't understand why this is the case. Is this not true if the interaction is mediated by the weak force?
  48. K

    Photon as composite of electron and positron

    A photon annihilates into an electron and a positron (both having spin 1/2). The reverse process is also a reality. Can the photon therefore be viewed as a composite of an electron and a positron having a total spin 1?
  49. B

    Is Time Travel the Key to Understanding Dirac's Equation and Positron Creation?

    When Dirac solved his equation, he found out there are negative energy levels and he did not know how to make of it. Then Feynman figured out if electron travel backward in time, then those negative energy levels will become positive energy level, and it will show up as a positron travel...
  50. C

    Positron and anti-proton existence

    So, I was recently think about something. Don't ask me how I thought of this, but positrons and anti-protons were on my mind all day and I thought of something. I thought about inertia. I thought about it and the more and more I did I figured that there must be something within matter that makes...
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