Hi, quick problem regarding emission of gamma ray.

Click For Summary

Homework Help Overview

The discussion revolves around a problem involving the emission of a gamma ray from an excited Fe (57) atom and the subsequent recoil of the nucleus. The subject area includes concepts of nuclear decay, photon momentum, and conservation of momentum and energy.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the setup of the problem, questioning how to apply conservation laws given the properties of photons. Some express confusion about the momentum of massless particles and how it relates to the recoil of the nucleus.

Discussion Status

There is ongoing exploration of the concepts involved, with some participants providing insights about photon momentum and its implications for the problem. A few have indicated progress in understanding the relationship between energy and momentum in this context.

Contextual Notes

Participants mention the need for clarity on the conservation of momentum and energy principles, as well as the implications of photons being massless yet possessing momentum. There is also a reference to a similar example from a textbook, indicating a potential gap in the original poster's understanding of the problem setup.

teclo
Messages
117
Reaction score
0
A Fe (57) atom is in an excited state 14.4 keV above the ground state. The nucleus decays to the ground state with the emission of a gamm ray. What's the recoil speed of the nucleus?

I'm not sure how to set this up. I thought a photon would have no mass, therefor no momentum. If so I couldn't do this with conservation of momenumtum or energy. I must be missing something, anyone have any ideas?
 
Physics news on Phys.org
The closest thing my book has to a simliar example is dealing with the Rutherford experiement.

K(1) + 0 = K(3) + K(4)

so i would think that the initial energy of the atom equals the energy of the photon plus the energy of the atom after emission. I'm not sure about how to setup something like this though.
 
teclo said:
I thought a photon would have no mass, therefor no momentum.
Despite being massless, photons do have momentum: p = E/c.
 
teclo said:
A Fe (57) atom is in an excited state 14.4 keV above the ground state. The nucleus decays to the ground state with the emission of a gamm ray. What's the recoil speed of the nucleus?

I'm not sure how to set this up. I thought a photon would have no mass, therefor no momentum. If so I couldn't do this with conservation of momenumtum or energy. I must be missing something, anyone have any ideas?

A photon DOES have a momentum.

http://scienceworld.wolfram.com/physics/Photon.html

Even the classical version of light as EM radiation has something called "radiation pressure".

So, knowing this, can you now do the problem?

Zz.
 
ZapperZ said:
A photon DOES have a momentum.

http://scienceworld.wolfram.com/physics/Photon.html

Even the classical version of light as EM radiation has something called "radiation pressure".

So, knowing this, can you now do the problem?

Zz.

yes, acutally i worked the problem out earlier. i forgot that p of the photon is E/c.

with that it was rather easy to approximate the recoil velocity of the nucleus using conservation of momentum. if reference frame observes initial excited nucleus as v of 0

0 = mv + E/c

i was making this harder than it really was
 

Similar threads

How to calculate gamma ray energies following beta decay?
  • · Replies 12 ·
Replies
12
Views
2K
Energy of the photon emitted in a gamma ray decay
  • · Replies 19 ·
Replies
19
Views
3K
High School Prevalence of nuclear decays accompanied by gamma emission
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Why KE of Annihilation Electrons Differs?
  • · Replies 11 ·
Replies
11
Views
2K
Undergrad Beta and gamma rays from radium
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad How to read this decay sheet (gamma emission after beta decay)
  • · Replies 4 ·
Replies
4
Views
2K
Graduate Beta/gamma decay probabilities
  • · Replies 2 ·
Replies
2
Views
2K
Estimating the energy of an emitted photon in gamma decay
  • · Replies 5 ·
Replies
5
Views
3K
Caesium 137 is an unstable isomer
  • · Replies 13 ·
Replies
13
Views
3K
Gamma ray irradiation and a shielded chamber question
  • · Replies 3 ·
Replies
3
Views
3K