Quick Pair Production question

6

Hello, I'm stuck on this relatively easy question but can't seem to find the answer in either my CGP revision guide, nor the rubbish Nelson thormes AQA A-level Physics book. Any help would be most grateful.

(b) (i) Explain why there is a minimum energy of the λ photon for this conversion to take place and what happens when a λ photon has slightly more energy than this value.

Reply 1

rbnphlp

11

desm0nd

Hello, I'm stuck on this relatively easy question but can't seem to find the answer in either my CGP revision guide, nor the rubbish Nelson thormes AQA A-level Physics book. Any help would be most grateful.

(b) (i) Explain why there is a minimum energy of the λ photon for this conversion to take place and what happens when a λ photon has slightly more energy than this value.

do you think we have telepathic ability to find out what conversion took place ..Post the whole q please..

Reply 2

lrn2physics

4

I'm guessing this is because the particle pairs have a certain mass, and this mass is related to the energy of the photon by e=mc^2. The energy is related to λ by, e = hc/λ

This leads us to hc/λ = mc^2
which gives, h/λ = mc
h and c are constants, so λ is inversely proportional to m. You can't create the particles, unless you have enough energy. There's a minimum energy requirement. However, if you have more than necessary energy, this "extra" energy is the kinetic energy of the particles.

All of this, of course, is just a guess.

Reply 3

Henoch

1

The conversion is from part a of the question where a Y photon(virtual) is converted into an electron and positron. (Basically pair production)

Reply 4

mondalani

1

this is due to Einsteins mass - energy equivalence theory.

Reply 5

charlotte792000

1

The gamma photon must have enough energy to provide the rest masses of the electron and positron. Any extra energy will provide the particles with kinetic energy

Quick Pair Production question

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