In normal MR practice, nuclei are excited and their spin states are detected by induction coils or cavities. Under these conditions, a theoretical physicist has to cope with the complex problem of the interaction of nuclear spins with the front-end device via non-radiative electromagnetic field. This raises conceptual difficulties and doubts which are still not completely settled, especially when one wants to reconcile in a single theoretical framework the evolution of macroscopic nuclear magnetization (Bloch equations and classical induction) with the quantum characteristics of NMR spectra with their complex Hamiltonians and sharp transitions.
Recent studies of spin noise radiation are throwing new light on these problems and raise new questions about the emission and absorption of electromagnetic radiation by spin systems and its phase coherence.
The topic has been brought up by the author in the context of long-range detection and/or stimulation of spin radiation which might pave a way for MR on scales ranging from sub-planetary to astronomical.
This poster adresses several properties of spin radiation, such as its chirality and directionality, proposes experiments which might clarify whether they obey classical or quantum rules, and speculates about what does the more likely latter case imply in terms of remote spin-radiation spectroscopy.
There is little doubt that the outcome of such experiments would also lead to further elucidation of those conceptual aspects of spin radiation which are still objects of heated discussions.
References and links:
- Hoult D.I., Ginsberg N.S.,
The Quantum Origins of the Free Induction Decay Signal and Spin Noise,
J.Magn.Resonance 148, 182 (2001).
- Sykora S.,
Magnetic Resonance in Astronomy: Feasibility Considerations,
XXXVI-th National Congress on Magnetic Resonance of GIDRM, Salerno (Italy), September 20-23, 2006.
- Sykora S.,
Perpectives of Passive and Active Magnetic Resonance in Astronomy,
22nd NMR Valtice meeting of Central European NMR Discussion Groups, Valtice (Czech Republic), April 15-18, 2007.