In the past few weeks, I have discovered that the experimentalist, unlike the theorist, its book-dwelling cousin, spends a majority of its time troubleshooting equipment. As discussed previously, NMR experiments are extremely demanding on experimenters and equipment alike – after all, we are manipulating atomic nuclei on a quantum level. Given the rigorous requirements of these experiments, it is natural that equipment failure will occur and technical problems will arise. Since my last post, the lab has faced a number of such technical problems, including a broken preamplifier, temperature controller, and probe. Each of these components play a necessary role in NMR experiments: the preamplifier, for instance, is necessary for data collection to occur. As previously mentioned, NMR measures the relaxation of magnetization vectors as they precess back to their equilibrium state. These precessions take place on the quantum level; as such, the resulting signals are incredibly small, usually on the order of microvolts (10-6 volts). Therefore, a powerful preamplifier is needed to boost the signal before it is sent to the analog-to-digital converters (ADCs) and onto the computer for signal averaging. Despite its relative importance, the broken preamp was only a minor inconvenience – there are several other preamps in the lab, which will be used until the broken amp is repaired or replaced.
I have spent the last two weeks calibrating and executing multiple pulse sequences. These sequences, once perfected, were used to further study the molecular structure of scandium oxide (Sc2O3). As stated earlier, NMR measures the response of atomic nuclei to radio-frequency pulses. Although a reasonable amount of information is obtainable from single pulses, the multi-pulse sequences I have been working with can be used in order to manipulate a sample’s quantum states. In one particular experiment, the “double frequency sweep,” a four pulse sequence is used to create “triple quantum coherence” in a scandium oxide sample.