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. scythe327

    B Can a hypothetical atom be made out of positrons and electrons ?

    I am a Computer Science Engineering student at a local university in India and I was really moved by the CERN youtube channel and it got me curious about the particles like electrons and protons, I love symmetry in nature and was not a huge fan of proton being nearly 2000 times the mass of...
  2. D

    Diagonalizing of Hamiltonian of electron and positron system

    What I did was first noting that ##\hat{\vec{S}}_1\cdot\hat{\vec{S}}_2=\frac{1}{2}(\hat{\vec{S}}^2-\hat{\vec{S}}_1^2-\hat{\vec{S}}_2^2)##, but these operators don't commute with ##\hat{S}_{1_z}## and ##\hat{S}_{2_z}##, this non the decoupled basis ##\ket{s_1,s_2;m_1,m_2}## nor the coupled one...
  3. P

    B 1-photon emission possible from electron-positron annihilation?

    I was reading about electron-positron annihilation. Typically it results in two photons, each with an energy of 511 keV, that go shooting out in opposite directions. But I read that in some instances three photons can result. Electrons have an intrinsic spin of ½, while photons have a spin of 1...
  4. M

    I Positron decay direction from muon

    Hello! I read that in the rest frame of a positive muon, decay positrons are preferentially emitted in the direction of the muon spin. Why is that the case? The decay is ##\mu^+\to e^+\nu_e\bar{\nu_\mu}##. Assuming that the positron is emitted at almost the speed of light, it will be a left...
  5. P

    Electron and positron collision producing a b0 meson pair

    Conservation of Energy: 9GeV + E = 5.3GeV + 5.3GeV Therefore E = 1.6GeV for the threshold energy. How would I find the velocity of B0 mesons so that I can calculate their mean distance? Then it would just be distance = velocity of b0 * mean proper lifetime Right?
  6. Mayan Fung

    I Why is a pair of an electron and a positron unstable?

    We know that an electron and a positron will annihilate and emit gamma ray. But the electron and positron possesses initial kinetic energy meaning that it is difficult for them to really collide in each other. Just like Earth is not dropping into the Sun even with the gravitational pull. So I am...
  7. K

    Minimum energy positron electron collision producing Z-boson

    Homework Statement Homework Equations m2 = E2 - p2 ([/B]The Attempt at a Solution I got stuck by not knowing how to handle the frames and I thought you can view the Z boson (CoM) frame, but then you simply get that mz = 2me
  8. P

    I The virtual photon can turn into a virtual electron positron?

    for example, when does an electron repel another electron with an electromagnetic disturbance?
  9. O

    A How are positrons used for fusion propulsion?

    Hi, I recently came across Positron Dynamics, a company working on a fusion propulsion system. You can watch this presentation given at Breakthrough Discuss 2018. They also got a grant from NIAC. Rather than trying to create and store positrons, they use Na-22 as a source. They also patented...
  10. B

    A R value in electron positron annihilation

    In the calculation of R=σ(e+e-→hadrons)/σ(e+e-→μ+μ-) from BaBar experimental data at a center of mass energy of √s≈10 GeV i obtain R=5. Theoretically I should get a value of R=10/3. I know it has something to do with the resonances of ϒ mesons shown in the plot attached, but I don't know how to...
  11. ISamson

    Could lightning be creating antimatter in our atmosphere?

    A recent article from phys.org says that a Japanese team of scientists have detected gamma rays coming from lightning strikes, which react with atmospheric Nitrogen and release a positron. Who would have thought that!
  12. Q

    B Discovering the Elusive Positron g-Factor: A Comparison with CODATA's Best Value

    Hi. I registered recently. Maybe you can help me with the following. I have sought the value of the electron g-factor and abundant information has appeared, including the best value exposed in CODATA. With the value of the positron g-factor I have not been lucky. Comparative approaches of...
  13. D

    I Electron and positron annihilate

    Hi. I am just starting to self-study particle physics. Came across the following in some notes - Electron and positron annihilate to form a photon with zero momentum. I thought all photons had momentum due to the de Broglie equation ? Also 2 electrons scatter to form a photon with zero energy...
  14. Admiller

    I How many electron positron pairs are created

    How many electron positron pairs are created every second in a cubic meter of vacuum?
  15. J

    Final Velocity of Positron through Potential Difference

    Homework Statement If a positron (or electron antiparticle) beam is accelerated across a potential of 20 kV, find the final velocity v of the particles. Do this problem TWICE, once using MKS units (J for energy) and a second time using "modern" units (eV for energy). Use the following values...
  16. Jovian_Dsouza

    B Does an electron turn into a positron when hit by a photon?

    I read somewhere that an electron travels forward in time and a positron travels backwards.And when a photon hits the electron the direction of time for it reverses and it becomes a positron.Does an electron really turn into a positron when hit by a photon? why?
  17. Gummy_Bear

    Kinetic energy of positron and proton

    1.e problem statement, all variables and given/known data Two positrons and two protons are kept on the four corners of a square of side a. Positrons are kept at vertices A and C and protons are kept at B and D. let q denote the charge on both positron as well as the proton. So what is the...
  18. I

    I Is this Linear Accelerator Design Valid?

    Good Evening Everyone, A group of friends and I were having a mini-contest, to see who could theoretically make anti-matter using the most simplistic design in terms of cost and general complexity. The obvious choice for us was the Positron, due to low energy requirements on all fronts. One of...
  19. E

    How Does a Positron's Kinetic Energy Change with Magnetic Field Strength?

    Homework Statement A positron moves in a circular path of radius R due to a uniform magnetic field of strength B applied perpendicular to the plane of the circle. If B is varied, which of the following best represents a graph of the kinetic energy of the positron as a function of B so that the...
  20. MullaTheMech

    Difference Between an Electron and a Positron?

    [Mentor's Note: The first 4 posts have been split off from another thread.] I want to know why a electron has a different charge than a positron. lets use an electron and positron that came to be at the same time and place. They should have split something. Can someone explain what it is they...
  21. J

    Speed of a Positron: How Does Voltage Affect It?

    Homework Statement A positron is a particle with the same mass as an electron, but with a positive charge. If a positron begins with a speed of 1/10th the speed of light, and then moves from a high voltage region to a low voltage region, what happens to its speed? Ignore any gravitational...
  22. Nick tringali

    What happens when an electron and a positron meet?

    The question also wants a numerical answer, calculate the amount of energy released. I am helping my friend with this because she is bad at science, but she is in College. If anyone knows of any formulas that would be of use, i would appreciate it.
  23. klotza

    Insights The Basics of Positron Emission Tomography (PET) - Comments

    klotza submitted a new PF Insights post The Basics of Positron Emission Tomography (PET) Continue reading the Original PF Insights Post.
  24. Plok

    Is the sun positively charged?

    Hydrogen fusion as described by proton-proton chain reaction that dominates in the sun produces two positrons for each helium nucleus produced. These annihilate with free electrons while the number of protons remain the same. Over time the sun is supposed to become positively charged, yet the...
  25. Einstein's Cat

    Distance between positron and electron

    Is there a way in determining the distance between an electron and a positron as they anhilliate? If this figure has been determined already, what is it? Thank you very much for your help!
  26. K

    I Understanding Anti-Positron Chirality: The Confusion Explained

    please see the following conversaytion. he is saying in some point that the anti positron is right chiral and the says its left chiral... whats right ParoXoN • 4 years agoVery cool post! Thanks for that :) I'm a little confused though: You say towards the end: "The “anti-positron” (does not...
  27. F

    Creating a positron and a electron with a photon

    Homework Statement Hi everybody. I have to demostrate that a photon, no matter it's energy, will never be able to create a positron and an electron on it's own. Homework Equations E=Sqrt(m^2+p^2) as long as c=1 Conservation of energy Ei=Ef; initial energy is equal to final energy...
  28. blue_leaf77

    Distinguish between positron and proton

    Probably a basic question in this field but I haven't been able to find the answer upon internet search. Suppose I send a beam consisting of protons and positrons with a given momentum into a cloud chamber, how can then I tell them apart? My own rough guess: Suppose the two particles undergo...
  29. A

    Why must an electron-positron collision produce gamma rays?

    Or, more specifically, what determinates the frequency of the photons emitted by a such a collision. I know that the number of photons produced depends on the spin and energy states of the initial particles.
  30. END

    Unfixed charges released from rest

    Homework Statement a.) [/B]A proton and an "positron" (identical to an electron, except positively charged) are brought ##5µm## apart and released from rest. What is the initial potential energy stored by this system? b.) In all of the previous problems on this homework, the system's...
  31. arpon

    What is the minimum energy required to produce an electron-positron pair?

    Homework Statement The antiparticle of electron is positron, whose mass is the same as electrons, i.e. 9.1 * 10^{-31} kg but the charge is opposite. What is the minimum energy required to produce a electron-positron pair? 2. Homework Equations E = mc^2 The Attempt at a Solution Actually I...
  32. S

    Why Do Positrons Lose Energy Before Annihilating With Electrons?

    I thought that when positrons and electrons collide they annihilate straight away, giving up energy in forms of photons and other particles. However, I'm reading through some notes and they suggest that the positron loses energy rapidily in collisions with electrons but does not annihilate until...
  33. J

    Positron to replace proton as the nucleus of an atom

    I know that the positron and electron have the same mass, which allows them to annihilate, and I know how solve the 2 body Schrodinger for a standard hydrogen atom to get the orbitals. My question is why the math works out the way it does. Is there an "intuitive" (I use that word cautiously)...
  34. R

    Electron Positron Annihilation

    What kinds of particles do e- and e+ annihilation make? Where does the higgs boson come into play? And why are the electromagnetic and the weak force so closely related? Thanks peeps
  35. V

    Cross section in muon pair production from electron positron annihilat

    I have a question regarding the calculation of the cross section in muon pair production from electron positron annihilation. After some calculations the textbook comes to the conclusion that the differential cross section is approximately equal to: (1+cos(theta)^2)alpha^2/(4*s) where alpha...
  36. W

    Antimatter-Matter Annihilation (i.e. antiproton w/ positron)

    I know that a particle's exact anti-counterpart (i.e. an electron and positron) will annihilate into pure energy. But my question is do differing particles and antiparticles (such as an antiproton and positron) annihilate each other, and if so how much so, because I doubt it too would result in...
  37. W

    Why does positron not annihilate sooner in cloud chamber experiment

    Specifically in Carl D Anderson's cloud chamber experiment, the first experiment to prove the existence of the positron, a positron travels through all of these mediums: glass, charged liquid particles, water vapor, and lastly passes through a lead plate. If antimatter is suppose to anihilate...
  38. xortdsc

    Energy of electron + positron separated by distance

    Hi, given the scenario of an electron and a positron (both assumed to be stationary) being separated by a given distance how could i compute the energy of that system ? The total energy would certainly contain the rest-mass-energies of both particles, but I'm struggling to incorporate the...
  39. R

    Decay of a proton into a positron and a neutral pion

    p -> e+ + pi° is >10^33 years. what conservation law does this limit test? p is uud pi° is uu or dd where the second quark of each is an antiquark baryon number is not conserved 1 = 0 + 0 charge is conserved lepton number is not conserved 0 = -1 + 0 not sure what this...
  40. C

    Pair Production, electron and positron from isolated photon

    I don't completely understand why an electron positron pair cannot be created from an isolated photon. I understand it must have something to do with 4 momentum conservation, but I really can't see a problem given the photon has enough energy for the mass to energy vice versa conversion.\ The...
  41. LotusTK

    Positron Emission: Overview & Changes

    Hi, i have a question here, but i don't know how to write a lengthened answer on it. I just know what happens and that's about it. Questions: A positron can be produced by pair production or by positron emission from a proton rich nucleus. a) Describe the changes that take place in a...
  42. A

    Simple positron diffraction problem

    Homework Statement A beam of positrons (positron ≡ antielectron) travels at 0.001% the speed of light and impinges on a slit that is 1 μm wide. Use modern units to find the angle θ between the center line and 3rd minimum of the resulting diffraction pattern. How far away (in cm) would you...
  43. T

    A proton and an positron (identical to an electron, except positivel

    A proton and an "positron" (identical to an electron, except positivel Homework Statement A proton and an "positron" (identical to an electron, except positively charged) are brought 6 µm apart and released from rest. a.) What is the initial potential energy stored by this system...
  44. R

    What happens when an electron and positron collide

    I was listening to this radio program (Google: In Our Time Antimatter) and they kept saying that when an electron and a positron collide they annihilate and radiate energy. I have a feeling that that's not right. I have a hunch that the particles turn into something else which then radiates...
  45. D

    Annihilation of electron positron pair

    Suppose in thought experiment one electron positron pair is annihilated in the carriage of fast moving train while the other pair is annihilated on the platform . Will the frequency of the photon reaching the platform from the carriage will be same as given out by the other pair which which is...
  46. PsychonautQQ

    Total Energy of 2 Photons from Positron-Electron Boom

    so if a positron and an electron boom each other and create 2 photons, how do I tell the total energy of the two photons? does a positron have anti mass equal to the magnitude of the electron? so the two photons total energy would be 2(m_e)*c^2
  47. Superposed_Cat

    Why is an electron a positron going backwards in time?

    Hi all, I was wondering how wheeler came to the conclusion that an anti-particle is a particle going backwards through time?
  48. S

    High energy electron positron branching ratios.

    Homework Statement Why does the ratio: \frac{σ(e^- + e^+ \rightarrow μ^- + μ^+) }{σ(e^- + e^+ \rightarrow τ^- + τ^+)} tend to unity at high energies and would you expect the same for: \frac{σ(e^- + e^+ \rightarrow μ^- + μ^+) }{σ(e^- + e^+ \rightarrow e^- + e^+)} The attempt at...
  49. L

    Why can positron go unobstructed through lead?

    Can anyone explain why a positron, in a charged magnetic field, is able to go through a 6mm lead plate, as seen in Anderson's positron experiment? Initially I thought that it could be quite similar to the gold foil experiments, but one of the features of the gold foil experiments is that it...
  50. S

    Positron cross section with H,D,T

    I have a question about cross section probability for a positron (e+) to interact with the electron (e-) that would be bound to three different atomic systems (1) hydrogen atom: H(e-), (2) deuterium atom: D(e-), (3) tritium atom: T(e-). My hypothesis is that a positron (e+) would have the...