Nuclear Magnetic Resonance
Chapter 4, page 1
4
Nuclear Magnetic Resonance
Pieter Zeeman observed in 1896 the splitting of optical spectral lines in the field of an electromagnet. Since then, the splitting of energy levels proportional to an external magnetic field has been called the "Zeeman effect". The "Zeeman resonance effect" causes magnetic resonances which are classified under radio frequency spectroscopy (rf spectroscopy).
In these resonances, the transitions between two branches of a single energy level split in an external magnetic field are measured in the megahertz and gigahertz range. In 1944, Jevgeni
Konstantinovitch Savoiski discovered electron paramagnetic resonance. Shortly thereafter in
1945, nuclear magnetic resonance was demonstrated almost simultaneously in Boston by
Edward Mills Purcell and in Stanford by Felix Bloch. Nuclear magnetic resonance was sometimes called nuclear induction or paramagnetic nuclear resonance. It is generally abbreviated to NMR. So as not to scare prospective patients in medicine, reference to the
"nuclear" character of NMR is dropped and the magnetic resonance based imaging systems
(scanner) found in hospitals are simply referred to as "magnetic resonance imaging" (MRI).
4.1
The Nuclear Resonance Effect
Many atomic nuclei have spin, characterized by the nuclear spin quantum number I. The absolute value of the spin angular momentum is
L = h I ( I + 1) .
(4.01)
The component in the direction of an applied field is
Lz = Iz h ≡ m h.
(4.02)
The external field is usually defined along the z-direction. The magnetic quantum number is symbolized by Iz or m and can have 2I +1 values:
Iz ≡ m = −I, −I+1, ..., I−1, I.
(4.03)
It holds for I that
I is half-integer for uneven mass numbers;
I is a whole number for even mass numbers but uneven proton numbers;
I is zero for even mass numbers and even numbers of protons.
The nucleus 1H is studied in the greatest number of NMR papers. In Current Contents©
4
Nuclear Magnetic Resonance
Pieter Zeeman observed in 1896 the splitting of optical spectral lines in the field of an electromagnet. Since then, the splitting of energy levels proportional to an external magnetic field has been called the "Zeeman effect". The "Zeeman resonance effect" causes magnetic resonances which are classified under radio frequency spectroscopy (rf spectroscopy).
In these resonances, the transitions between two branches of a single energy level split in an external magnetic field are measured in the megahertz and gigahertz range. In 1944, Jevgeni
Konstantinovitch Savoiski discovered electron paramagnetic resonance. Shortly thereafter in
1945, nuclear magnetic resonance was demonstrated almost simultaneously in Boston by
Edward Mills Purcell and in Stanford by Felix Bloch. Nuclear magnetic resonance was sometimes called nuclear induction or paramagnetic nuclear resonance. It is generally abbreviated to NMR. So as not to scare prospective patients in medicine, reference to the
"nuclear" character of NMR is dropped and the magnetic resonance based imaging systems
(scanner) found in hospitals are simply referred to as "magnetic resonance imaging" (MRI).
4.1
The Nuclear Resonance Effect
Many atomic nuclei have spin, characterized by the nuclear spin quantum number I. The absolute value of the spin angular momentum is
L = h I ( I + 1) .
(4.01)
The component in the direction of an applied field is
Lz = Iz h ≡ m h.
(4.02)
The external field is usually defined along the z-direction. The magnetic quantum number is symbolized by Iz or m and can have 2I +1 values:
Iz ≡ m = −I, −I+1, ..., I−1, I.
(4.03)
It holds for I that
I is half-integer for uneven mass numbers;
I is a whole number for even mass numbers but uneven proton numbers;
I is zero for even mass numbers and even numbers of protons.
The nucleus 1H is studied in the greatest number of NMR papers. In Current Contents©