Discussion
Electron and positron annihilate and produce a single photon only when :
Answer: D
A single photon can be produced only when at least one particle is in a bound state.
For a free electron and positron, energy and momentum cannot both be conserved if only one photon is emitted. In the centre-of-momentum frame the total momentum is zero but the energy is at least \(2m_{e}c^{2}\); a single photon with that energy would carry momentum \(E/c \neq 0\). So free-pair annihilation gives at least two photons.
If one of the particles is bound, for example an electron bound in an atom, the nucleus or the rest of the atom can take up the recoil momentum, and one-photon annihilation becomes possible. Having one or both particles at rest does not help, since the centre-of-momentum argument still applies.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development