Pair production

Announcements
    • Thread Starter
    Offline

    1
    ReputationRep:
    Hi everyone I was wondering is someone could give me an explanation of pair production and an example of pair production as I am struggling with the way that my teacher has explained it.
    Many thanks
    Offline

    0
    ReputationRep:
    Hi! I'm assuming you mean in particle physics? We've just covered that at school (I'm studying AQA A Level and I'm in Year 12) so I'll try my best to explain...
    Occasionally, gamma rays (very high frequency electromagnetic waves) spontaneously create a particle (eg an electron) and an antiparticle (eg a positron - the antimatter counterpart of an electron, with the same mass but an opposite charge).
    Gamma rays, like all electromagnetic waves, are made up of photons (little packets of energy that act like particles). In pair production, an individual photon splits up into a particle and an antiparticle.
    Pair production is more likely to happen if the gamma ray has just passed a nucleus.
    In order for a photon to split into a particle and antiparticle, it needs enough energy - it needs at least as much energy as the particle and antiparticle have when they aren't moving (their rest energy, which should be on your data sheet if you have one?)
    A particle and its corresponding antiparticle have the same rest energy, so to work out how much energy is needed you have to multiply the rest energy of the particle by two. The units for that are usually mega electron volts (MeV), but sometimes they'll ask you to convert that into joules - one MeV = 1.6x10 to the power of 13 Joules, so times the answer in MeV by 1.6x10 to the 13.
    Using this method you can work out whether the pair production is possible- if the photon has at least enough energy as is needed, it is possible, if not it is impossible.
    If the photon has more energy than is needed the particle and antiparticle gain that energy as kinetic energy.

    For example...
    A photon spontaneously converts into an electron and a positron. The photon has 2.0x10 to the -13 joules of energy. The minimum energy needed for this pair production is 0.51 MeV (roughly the rest energy of an electron or a positron) x 2 (because two particles with this rest energy are created). This is 1.02 MeV which is 1.02x1.6x10 to the -13 Joules which is 1.64x10 to the -13 Joules (ish). The extra 0.36x10 to the -13 Joules are converted into kinetic energy which the electron and positron gain.


    I think that's everything! Sorry if it's overcomplicated/unclear - and sorry it's so long! I have trouble being concise
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by donttellme)
    Hi! I'm assuming you mean in particle physics? We've just covered that at school (I'm studying AQA A Level and I'm in Year 12) so I'll try my best to explain...
    Occasionally, gamma rays (very high frequency electromagnetic waves) spontaneously create a particle (eg an electron) and an antiparticle (eg a positron - the antimatter counterpart of an electron, with the same mass but an opposite charge).
    Gamma rays, like all electromagnetic waves, are made up of photons (little packets of energy that act like particles). In pair production, an individual photon splits up into a particle and an antiparticle.
    Pair production is more likely to happen if the gamma ray has just passed a nucleus.
    In order for a photon to split into a particle and antiparticle, it needs enough energy - it needs at least as much energy as the particle and antiparticle have when they aren't moving (their rest energy, which should be on your data sheet if you have one?)
    A particle and its corresponding antiparticle have the same rest energy, so to work out how much energy is needed you have to multiply the rest energy of the particle by two. The units for that are usually mega electron volts (MeV), but sometimes they'll ask you to convert that into joules - one MeV = 1.6x10 to the power of 13 Joules, so times the answer in MeV by 1.6x10 to the 13.
    Using this method you can work out whether the pair production is possible- if the photon has at least enough energy as is needed, it is possible, if not it is impossible.
    If the photon has more energy than is needed the particle and antiparticle gain that energy as kinetic energy.

    For example...
    A photon spontaneously converts into an electron and a positron. The photon has 2.0x10 to the -13 joules of energy. The minimum energy needed for this pair production is 0.51 MeV (roughly the rest energy of an electron or a positron) x 2 (because two particles with this rest energy are created). This is 1.02 MeV which is 1.02x1.6x10 to the -13 Joules which is 1.64x10 to the -13 Joules (ish). The extra 0.36x10 to the -13 Joules are converted into kinetic energy which the electron and positron gain.


    I think that's everything! Sorry if it's overcomplicated/unclear - and sorry it's so long! I have trouble being concise
    That is brilliant thanks so much i am in year 12 doing the same thing too xx
 
 
 
Write a reply… Reply
Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: September 27, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Poll
Which is the best season?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Sponsored content:

HEAR

HEAR

Find out how a Higher Education Achievement Report can help you prove your achievements.

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.