The MRI medical procedure uses a technique called magnetic resonance imaging. It uses the magnetic moment of the proton to provide an imaging signal. Since the human body is 70% water (H₂O), there are a large number of protons in the hydrogen atoms to image. The patient is placed in a strong magnetic field. The magnetic moments of the protons align themselves with the magnetic field. A transition between magnetic spin states gives the signal.

Like the electron, the proton has instrinsic spin of 1/2. The magnetic moment of the proton is m_N, where m_N, called the is nuclear magneton, is given by the expression (m_p is the mass of the proton):

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a) What is the ratio of the magnetic moment of the electron to the magnetic moment of the proton?

m_e / m_p =

b) In an external magnetic field the proton's two spin magnetic states, m_s = +1/2 and -1/2, have different energies. What is the difference in the energy, DE, of the two states in a magnetic field of Tesla?

DE = eV.

Transitions between the two magnetic states can be induced by the absorption of a photon of the appropriate frequency.

c) In a magnetic field of x.x Tesla, what is the frequency, f, of the photon that could be absorbed?

f = MHz

The magnetic spin states of the electron also have different energies.

d) What frequency photons would cause transitions between the electrons' magnetic spin states in this situation?

f = MHz