Procedure

The steps in each measurement are outlined in the manual. Here’s a general guideline:

1. Section B directs students to reset the instrument to some listed default settings. DO NOT DO THAT! It can be incredibly difficult to find the right settings when you don’t have even a small signal to start from. The instrument has been pre-set with not-very-incorrect settings.
2. You’ll be using heavy mineral oil for ALL of your experiments. If you finish your prescribed measurements and have time to use a different sample, then go for it!
3. Insert the pickup probe and make sure that the pulse of the weak oscillating field is working. Make sure the timebase of the oscilloscope is appropriate for the signal you are measuring. The pickup probe is too long and reaches down past the center of the magnet. Pull it up just a tiny bit and use a bit of tape to keep it in place. If you don’t pull it up a bit, you won’t be able to reach a 40-V peak-to-peak pulse measurement.
4. Adjust the timebase of the scope and insert the sample. Adjust the instrument parameters until you have an FID signal like the one in Figure 3.4. This is your ‘90’ pulse. The parameters you should adjust are highlighted in the manual in the lab. Ignore any instructions from the manual about changing the sample. WARNING: some parameters do NOT change the signal monotonically.
5. Adjust the tuning capacitors gently. Excessive force is not required. Adjust the course one first, then the fine one. Do not put anything magnetic anywhere near the magnet. You may not be able to get it back. You do not have to adjust the pickup capacitors on the opposite side of the sample slot.
6. The length of the A pulse is between 2 and 3 s. If you are getting a larger signal by making the length of the A pulse much longer than that, then your tuning capacitors probably need adjusting or you are not at the true resonant frequency.
7. You will determine the spin-lattice relaxation time () and the spin-spin relaxation time (). Don’t measure  by decreasing the pulse repetition time; it just isn’t precise enough to be meaningful. Use the method from Section D.1.b where you use a 180 pulse, wait a time , then apply a 90 pulse.
8. Measure  using the method in Section D.2.b. You should be generating scope traces similar to the one in Figure 3.7.

This apparatus is incredibly versatile, and can be used to measure the relaxation times in a wide variety of samples, and use that information to make determinations about the samples, such as biological material, rubber, various fluorinated compounds, and see if you can distinguish the difference between recycled and new TEFLON. These experiments are not easy and, depending on your choice, your lab tech or TA may not have already attempted them.