Gamma ray coincidence and multipoles

In summary, the conversation discusses an experiment on gamma ray coincidence from Co-60 and aims to deduce the angular momentum of the first excited state, which indicates the type of multipole that the state is. The concept of multipole refers to the Fourier expansion of a function into spherical harmonics, with different values of L corresponding to different types of multipole. The conversation also mentions spin degeneracy and the meaning of multipole in relation to magnetic moment.
  • #1
miss_mayhem
1
0
Dear Physics Forums,

I am currently conducting an experiment on gamma ray coincidence from Co-60. Co-60 decays to an excited state, then de-excited by emitting two gamma rays. The aim is to deduce the angular momentum L of the first excited state.

Apparently L indicates the type of multipole that the first state is. I can't seem to find any information on this, but what I know so far is that L=1 is a multipole, L=2 is a quadrupole etc.. But I do not understand how this is calculated from L. Is it something to do with spin? I'm currently imagining that spin degeneracy is 2 for a photon, and so if L=2 then 2x2=4 which tells us that this state is quadrupole. I'm a bit fuzzy on this.

Also, I am not entirely sure what 'multipole' is meant to mean - something to do with magnetic moment? I would be extremely grateful for a brief explanation of this, I hope I'm not being too demanding!

Thanks guys!
 
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  • #2
Multipole in this context refers to the Fourier expansion of an arbitrary function into spherical harmonics.

[tex] f(\theta,\phi) = \sum_{\ell,m} c_{\ell, m } Y_{\ell m} (\theta,\phi).[/tex]

If we were to expand a dipole interaction in this way, we'd find that only the [tex]\ell=1[/tex] term contributes. A quadrapole corresponds to the [tex]\ell =2[/tex] term, etc. So this terminology is used to refer to the moments that let us calculate the

[tex]c_{\ell,m}\sim \int d\Omega Y^*_{\ell m} f(\theta,\phi).[/tex]
 

1. What is gamma ray coincidence?

Gamma ray coincidence is a process in which two or more gamma rays are emitted from a radioactive nucleus at the same time, indicating that the nucleus has undergone a specific decay. This type of coincidence is used in gamma ray spectroscopy to identify and study different nuclear reactions and processes.

2. How is gamma ray coincidence detected?

Gamma ray coincidence is detected by using specialized equipment such as gamma ray detectors, scintillators, and coincidence circuits. These instruments can detect and record the arrival of gamma rays, their energy, and the time between their detections. By analyzing these data, scientists can determine whether the gamma rays were emitted in coincidence or not.

3. What are gamma ray multipoles?

Gamma ray multipoles refer to the different types of radiation that can be emitted from a nucleus during a nuclear reaction or decay. These include electric and magnetic dipole, quadrupole, and higher multipole radiations. Each type of multipole has a unique energy and angular distribution, which can be measured and analyzed to understand the underlying nuclear processes.

4. How are multipoles related to gamma ray coincidence?

In gamma ray coincidence, the detection of two or more gamma rays indicates that the nucleus has undergone a specific decay, which can be described in terms of multipole radiation. By analyzing the energies and angular distributions of the coincident gamma rays, scientists can determine the type and strength of the multipole radiation involved in the decay process.

5. What are the applications of gamma ray coincidence and multipoles?

Gamma ray coincidence and multipoles have numerous applications in nuclear physics, astrophysics, and other fields. They are used to study nuclear reactions, identify and characterize radioactive isotopes, and understand the structure and properties of nuclei. They are also used in medical imaging techniques such as positron emission tomography (PET) scans, where gamma ray coincidence is used to detect the annihilation of positrons in the body.

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