Are RF Photons Present in NMR Spectroscopy?

[Frank Peters]

Some will claim that RF energy being composed of photons can only be accepted on faith because there is no experimental evidence and there probably will be no experimental evidence due to the comparatively long wavelenghts of RF waves.

But the technique of NMR (nuclear magnetic resonance) spectroscopy produces RF energy from the decay of excited nuclear spin states. Is this not the actual production of RF photons?

NMR frequncies can be as low as 70-100 megahertz and thus the NMR apparatus gives experimental evidence for RF photons at this relatively low frequency range.

Is this a correct assessment?

 

[Lord Jestocost]

See, for example, the 21 cm Hydrogen line: https://en.wikipedia.org/wiki/Hydrogen_line

 

[tech99]

Some will claim that RF energy being composed of photons can only be accepted on faith because there is no experimental evidence and there probably will be no experimental evidence due to the comparatively long wavelenghts of RF waves.

But the technique of NMR (nuclear magnetic resonance) spectroscopy produces RF energy from the decay of excited nuclear spin states. Is this not the actual production of RF photons?

NMR frequncies can be as low as 70-100 megahertz and thus the NMR apparatus gives experimental evidence for RF photons at this relatively low frequency range.

Is this a correct assessment?

As far as I can see, NMR is just a resonance effect. The nuclei are not radiating, they just respond to a pulse of field and then continue to oscillate for a period of time. It is outwardly the same as an LC circuit. The size of the "experiment" is small compared to the wavelength, so we are probably dealing with induction fields for the most part, rather than radiation of photons by the nuclei.

 

[mfb]

See, for example, the 21 cm Hydrogen line: https://en.wikipedia.org/wiki/Hydrogen_line

.. and in particular, masers based on this. They were built before the first lasers.

 

[tech99]

See, for example, the 21 cm Hydrogen line: https://en.wikipedia.org/wiki/Hydrogen_line

The Hydrogen Line comes from electron transition which is a different effect to NMR.

 

[mfb]

So what? It is in the RF-range, and photons are necessary to understand the observations of the line.

 

[Frank Peters]

As far as I can see, NMR is just a resonance effect.

So you are saying that NMR is not a quantum effect, even though the frequency of the radiation is equal to the difference between the nuclear spin states according to E = hv.

As has been mentioned, the maser is a good example of RF photons but the frequency of a maser is an order of magnitude higher than that of NMR. I wonder if it is possible to find quantum transitions that coorespond to even lower frequencies.

 

[ZapperZ]

As far as I can see, NMR is just a resonance effect. The nuclei are not radiating, they just respond to a pulse of field and then continue to oscillate for a period of time. It is outwardly the same as an LC circuit. The size of the "experiment" is small compared to the wavelength, so we are probably dealing with induction fields for the most part, rather than radiation of photons by the nuclei.

This is incorrect.

The MACROSCOPIC effect, or the bulk magnetization, may be describe via classical effect, but the MICROSCOPIC effect can't. For example, how do you account for the population of spins in each state once the degeneracy has been removed in a magnetic field? This population fraction determines the strength of the signal that you get at a particular temperature.

The fact that NMR uses the property of the splitting of such spin states (something that is absent in classical description) clearly indicates that, at the most fundamental level, NMR is a quantum effect.

Zz.

 

[tech99]

Thank you.

 

[Frank Peters]

at the most fundamental level, NMR is a quantum effect.
Zz.

That seems to answer my original question. We can look upon NMR spectroscopy as being an experimental verification for the existence of RF photons.

Does science know of any nuclear/atomic/molecular transitions that would correspond to even lower radio frequncies? As I mentioned, NMR transitions usually correspond to frequencies around 75-100 MHz.

 

[tech99]

That seems to answer my original question. We can look upon NMR spectroscopy as being an experimental verification for the existence of RF photons.

Does science know of any nuclear/atomic/molecular transitions that would correspond to even lower radio frequncies? As I mentioned, NMR transitions usually correspond to frequencies around 75-100 MHz.

Apologies if I am mistaken in this, but I understood that the resonant structure - the nucleus - is given an RF pulse so it rings. We then measure that frequency. We are not using the pulse to pump the energy of the nucleus up somehow so we observe a transition. That is why I suggested that the nucleus behaves like an LC circuit, a passive device.

 

[ZapperZ]

Apologies if I am mistaken in this, but I understood that the resonant structure - the nucleus - is given an RF pulse so it rings. We then measure that frequency. We are not using the pulse to pump the energy of the nucleus up somehow so we observe a transition. That is why I suggested that the nucleus behaves like an LC circuit, a passive device.

I don't understand this, and I bet you don't quite understand some of the basic operations of an NMR setup.

1. The material is put in a STATIC magnetic field. This then breaks the degeneracy of the magnetic splitting.

2. An ADDITIONAL pulse can then be sent to the material. This pulse may induced a number of things, such as a 90-degree flip of the bulk magnetization (a spin-lattice relaxation process) or a 180-degree flip (a spin-spin relaxation process).

Both of those processes involve changing the population of higher and lower spin states for a brief period of time. So you are, in essence, "pumping" the nucleus into an excited "spin" state.

Zz.

 

[mfb]

Does science know of any nuclear/atomic/molecular transitions that would correspond to even lower radio frequncies? As I mentioned, NMR transitions usually correspond to frequencies around 75-100 MHz.

You could do NMR with weaker magnetic fields.
Where is the point? 100 MHz in one reference frame is 1 Hz in another.

 

[f95toli]

Apologies if I am mistaken in this, but I understood that the resonant structure - the nucleus - is given an RF pulse so it rings. We then measure that frequency. We are not using the pulse to pump the energy of the nucleus up somehow so we observe a transition. That is why I suggested that the nucleus behaves like an LC circuit, a passive device.

It really only depends on the field you are using. In ultra-low field NMR (which can be done in the Earth's background field) the frequencies involved are much lower (kHz), but then the signal is lower since the degree of polarization is much lower.