why radio frequency

[nbkoneru]

Dear sir,

Why we are using radio frequency excluding other electro magnetic radiation.

thankx

[R2-D2]

Originally posted by nbkoneru@Jun 22 2006, 04:25 AM
Dear sir,

Why we are using radio frequency* excluding other electro magnetic radiation.

thankx

[snapback]169[/snapback]

I am just learning all this NMR theory too, so if anyone reads this and Im misguided please correct me.

The nuclei used in biological NMR all have spin I=1/2. This means that there are 2I+1=2 energy levels possible. These two energy levels are the lower energy state, where the magnetic moments of the nucei are parrallel to the magnetic field, and the high energy state, where the nuclei are antiparrallel to the magnetic field. The difference between these two energy levels is given by the equation E=(gyromagnetic ratio)(plank's constant/2*pi)(magnetic field). So for a 16.4 T magnet, the difference in energy states for proton would equal 4.672e-25 J. Using E=hv you find that the frequency needed to excicte nuclei from the lower to upper energy level is 7.05e8 /s, which falls in the range of radio frequency. If you do this with all the other spin 1/2 nuclei (15N,13C,31P) you find that these fall within that range as well. So to make a long story short, radio frequency is used because it provides sufficient energy to make the transition from the lower energy state to the higher energy state needed for excitation of the nuclei during an experiment.