Vector Precession and Components

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Questions and Answers

What is true about the vector model in NMR?

It is a new concept introduced recently

It has no relevance in understanding NMR experiments

It can be applied to all types of NMR experiments

It is limited in its application to only a few situations (correct)

Why is it important to have a good grasp of the vector model in NMR?

To apply it to all types of NMR experiments

To use as a language for basic NMR experiments

To simplify the understanding of complex NMR experiments (correct)

To restrict its usage in sophisticated treatments

How is the behavior of the nucleus described in the vector model?

As a large energy spectrum

As a magnetic field generator

As an energy level source

As a small bar magnet (correct)

What role does the interaction with an applied magnetic field play in NMR?

It gives rise to the energy levels and ultimately an NMR spectrum Signup and view all the answers

In the rotating frame, what is the apparent Larmor frequency?

Difference between the Larmor frequency and the rotation frequency of the frame Signup and view all the answers

What is the reduced field in the rotating frame?

The difference between the Larmor frequency and the rotation frequency of the frame Signup and view all the answers

What happens when choosing the rotating frame to be at the Larmor frequency?

Both offset and reduced field are zero Signup and view all the answers

What is the effective field in the rotating frame?

Vector sum of the reduced field and the RF field Signup and view all the answers

What is used to describe the orientation of magnetization with respect to the effective field?

Tilt angle Signup and view all the answers

What is a special case where the transmitter frequency is exactly the same as the Larmor frequency?

On-resonance pulse Signup and view all the answers

What type of motion does the magnetization vector execute when tilted away from the z axis?

Precessional motion Signup and view all the answers

What is the name of the net magnetic field along the direction of the applied field at equilibrium?

Bulk magnetization Signup and view all the answers

What induces a current in the coil wound around the x axis?

Precessing magnetization Signup and view all the answers

In an NMR experiment, which component of the magnetization vector is detected by placing a coil along the xy-plane?

X-component Signup and view all the answers

What frequency is the same as the frequency of the line observed in the NMR spectrum?

Larmor frequency Signup and view all the answers

What term describes the angle the magnetization vector makes with the x axis after a certain time?

Larmor angle Signup and view all the answers

What represents the net magnetization and points along the direction of the applied field (z axis)?

Bulk magnetization Signup and view all the answers

What is the term for the motion of the magnetization vector when it is tilted away from the z axis?

Precessional motion Signup and view all the answers

What happens to the net magnetic field at equilibrium if there is no alignment of magnetic moments?

It becomes zero Signup and view all the answers

What happens to the net magnetization at equilibrium if there is no alignment of magnetic moments?

It becomes zero Signup and view all the answers

What is responsible for inducing a current in a coil wound around the x axis?

Precessional motion Signup and view all the answers

What can be used to rotate the magnetization away from its equilibrium position in the presence of a strong magnetic field?

Radiofrequency field Signup and view all the answers

What is the angle of precession denoted by in the text?

ω0t Signup and view all the answers

What is used to replace the magnetic field along the z-axis with one in the xy-plane to bring the magnetization down from the z-axis?

Resonance Signup and view all the answers

What concept is used to apply a small oscillating magnetic field along the x-axis at or near the Larmor frequency?

Resonance Signup and view all the answers

What is used to produce the oscillating magnetic field that can rotate the magnetization, even in the presence of a strong applied field?

Radiofrequency field Signup and view all the answers

Which fields add up to give a linearly oscillating field along the x-axis according to the text?

B+1 and B−1 Signup and view all the answers

What happens to the x-component as the angle of rotation approaches 12π radians (90°)?

It shrinks towards zero Signup and view all the answers

What is significant in the interaction between the magnetization and the rotating field in the same direction of rotation according to the text?

B+1 Signup and view all the answers

What is the angle by which the magnetization vector is rotated during an RF pulse?

ω1 tp Signup and view all the answers

What is the common flip angle used in NMR experiments?

π Signup and view all the answers

Which plane does the magnetization vector precess during an on-resonance 90° pulse?

xy-plane Signup and view all the answers

What is the term used for pulses where the RF field is much larger than the reduced field, effectively placing all resonances on-resonance?

Hard pulses Signup and view all the answers

In which frame does the signal appear to oscillate at the offset frequency Ω instead of the Larmor frequency?

Rotating frame Signup and view all the answers

How many periods does the simplest NMR experiment, known as pulse-acquire, consist of?

Three periods Signup and view all the answers

What happens to the equilibrium magnetization during a 90° pulse?

It rotates onto the y-axis Signup and view all the answers

During which period does the magnetization precess in the transverse plane at the offset frequency Ω?

Signal detection period Signup and view all the answers

What is the simplest NMR experiment known as?

Pulse-acquire Signup and view all the answers

What axis does a 90° pulse rotate equilibrium magnetization onto?

y axis Signup and view all the answers

At what frequency does the signal appear to oscillate in the rotating frame?

Offset frequency Ω Signup and view all the answers

What is the term used for pulses where all resonances are placed on-resonance?

Hard pulses Signup and view all the answers

Study Notes

The magnetization vector in NMR precesses about the applied magnetic field, rotating in the zy-plane with frequency ω1.
During an RF pulse of duration tp, the magnetization vector is rotated by an angle β = ω1 tp, also called the flip angle.
Commonly used flip angles are π/2 (90°) and π (180°).
A "grapefruit" diagram illustrates the magnetization vector's motion during on-resonance 90° and 180° pulses.
Hard pulses, where the RF field is much larger than the reduced field, effectively place all resonances on-resonance.
The signal detected in NMR experiments is in the rotating frame, where it appears to oscillate at the offset frequency Ω instead of the Larmor frequency.
The simplest NMR experiment, known as pulse-acquire, consists of three periods: equilibrium, RF pulse application, and signal detection.
During the equilibrium period, magnetization builds up along the z-axis.
A 90° pulse rotates this equilibrium magnetization onto the -y axis.
During the signal detection period, the magnetization precesses in the transverse plane at the offset frequency Ω.
Simple geometry helps deduce how the x- and y-magnetizations vary with time.

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Description

This quiz explores the precession of a vector and the calculation of its x and y components using simple geometry. It covers how the x-component is proportional to cosine and the y-component is negative and proportional to sine.

Vector Precession and Components

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Questions and Answers

What is true about the vector model in NMR?

Why is it important to have a good grasp of the vector model in NMR?

How is the behavior of the nucleus described in the vector model?

What role does the interaction with an applied magnetic field play in NMR?

In the rotating frame, what is the apparent Larmor frequency?

What is the reduced field in the rotating frame?

What happens when choosing the rotating frame to be at the Larmor frequency?

What is the effective field in the rotating frame?

What is used to describe the orientation of magnetization with respect to the effective field?

What is a special case where the transmitter frequency is exactly the same as the Larmor frequency?

What type of motion does the magnetization vector execute when tilted away from the z axis?

What is the name of the net magnetic field along the direction of the applied field at equilibrium?

What induces a current in the coil wound around the x axis?

In an NMR experiment, which component of the magnetization vector is detected by placing a coil along the xy-plane?

What frequency is the same as the frequency of the line observed in the NMR spectrum?

What term describes the angle the magnetization vector makes with the x axis after a certain time?

What represents the net magnetization and points along the direction of the applied field (z axis)?

What is the term for the motion of the magnetization vector when it is tilted away from the z axis?

What happens to the net magnetic field at equilibrium if there is no alignment of magnetic moments?

What happens to the net magnetization at equilibrium if there is no alignment of magnetic moments?

What is responsible for inducing a current in a coil wound around the x axis?

What can be used to rotate the magnetization away from its equilibrium position in the presence of a strong magnetic field?

What is the angle of precession denoted by in the text?

What is used to replace the magnetic field along the z-axis with one in the xy-plane to bring the magnetization down from the z-axis?

What concept is used to apply a small oscillating magnetic field along the x-axis at or near the Larmor frequency?

What is used to produce the oscillating magnetic field that can rotate the magnetization, even in the presence of a strong applied field?

Which fields add up to give a linearly oscillating field along the x-axis according to the text?

What happens to the x-component as the angle of rotation approaches 12π radians (90°)?

What is significant in the interaction between the magnetization and the rotating field in the same direction of rotation according to the text?

What is the angle by which the magnetization vector is rotated during an RF pulse?

What is the common flip angle used in NMR experiments?

Which plane does the magnetization vector precess during an on-resonance 90° pulse?

What is the term used for pulses where the RF field is much larger than the reduced field, effectively placing all resonances on-resonance?

In which frame does the signal appear to oscillate at the offset frequency Ω instead of the Larmor frequency?

How many periods does the simplest NMR experiment, known as pulse-acquire, consist of?

What happens to the equilibrium magnetization during a 90° pulse?

During which period does the magnetization precess in the transverse plane at the offset frequency Ω?

What is the simplest NMR experiment known as?

What axis does a 90° pulse rotate equilibrium magnetization onto?

At what frequency does the signal appear to oscillate in the rotating frame?

What is the term used for pulses where all resonances are placed on-resonance?

Study Notes

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