NMR: Difference between revisions

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* Shim - NMR relies on having a very homogeneous magnetic field. "Shimming" the magnet refers to adjusting it, and this is achieved by electronic coils that fine-tune the magnetic field. The term comes from the old days when shimming was achieved mechanically by using pieces of thin metal (shim stock) to manually adust the magnetic field, up hill, both ways.

* Shunt - A mechanical adjustment which slightly increases or decreases the magnetic field, thus changing the "field offset" and moving the peaks left or right along the x-axis. As the magnetic field strength drifts through time and temperature, this might be necessary if the machine has not been used in a while. Performing this adjustment requires a brass, copper, or wooden flathead to turn a screw deep inside the instrument. Use of a typical iron-containing screwdriver will result in it distorting the field (making adjustment challenging), and it'll try to consume the screwdriver the whole time you are trying (it's not worth it). There should be a thin copper tube pinched flat on one side around the instrument for this purpose.

* CW - Continuous Wave. Before modern signal processing with Fourier Transforms, we had instruments which would do a sweep with increasing magnetic field. This was slow.

* FID - Free induction decay. This is a view of the raw signal before applying a Fourier transform to it.

== History of NMR as a technique ==

@@ Line 87: / Line 87: @@
 * Shim - NMR relies on having a very homogeneous magnetic field. "Shimming" the magnet refers to adjusting it, and this is achieved by electronic coils that fine-tune the magnetic field. The term comes from the old days when shimming was achieved mechanically by using pieces of thin metal (shim stock) to manually adust the magnetic field, up hill, both ways.
 * Shunt - A mechanical adjustment which slightly increases or decreases the magnetic field, thus changing the "field offset" and moving the peaks left or right along the x-axis. As the magnetic field strength drifts through time and temperature, this might be necessary if the machine has not been used in a while. Performing this adjustment requires a brass, copper, or wooden flathead to turn a screw deep inside the instrument. Use of a typical iron-containing screwdriver will result in it distorting the field (making adjustment challenging), and it'll try to consume the screwdriver the whole time you are trying (it's not worth it). There should be a thin copper tube pinched flat on one side around the instrument for this purpose.
+* CW - Continuous Wave. Before modern signal processing with Fourier Transforms, we had instruments which would do a sweep with increasing magnetic field. This was slow.
+* FID - Free induction decay. This is a view of the raw signal before applying a Fourier transform to it.
 == History of NMR as a technique ==