Non-Fiction: Research Writing

Did I ever say this blog was going to be 100% about writing fiction? Well, here's a little treat for all of you... and mostly because I don't have time today to write anything real.

We got our physics papers back today, so I'm going to include some of that... hoorah for lower division classes and spending two nights on one assignment and using an organic chemistry textbook as a reference for a physics assignment. This was mostly a physical chemistry topic.

Although the most infamous aspects associated with nuclear physics are related to the atomic bombs that the United States dropped on Japan to end World War Two, nuclear physics has proven itself to have important applications in two closely-related areas that many people encounter on a regular basis. One is NMR, or nuclear magnetic resonance spectroscopy, which is often used to identify chemical compounds. Operating on the same basic principles is the MRI, which stands for magnetic resonance imaging.

The NMR takes advantage of the fact that energy levels are quantized. ∆E=h²n/4mL² (where ∆E is the change in energy between levels, h is Planck’s constant, n is an integer, m is the mass of the molecule and L is the wavelength required to excite the molecule to the next energy level) should prove that the energy is quantized, as 4, h, n and m are constants for any given molecule. This is one requirement for the NMR to work.

The other requirement is for there to either be an odd mass number or an odd atomic number on the molecule. If A=Z+N (A is the mass number, Z is the number of neutrons, N is the number of protons), then either A or N must be odd. This is so that the nucleus can spin. When the nucleus is spun, then angular momentum is generated. This makes a magnetic field. You can apply an external magnetic field and the nucleus’s magnetic field will either align or not align with the external magnetic field. The NMR rotates the nuclei by applying an external magnetic field and quantizes the energies.

The basic machinery for the NMR requires four parts: a magnet, a radio frequency transmitter, a detector that can measure how much energy the molecule absorbs and a something to record output versus how much magnetic field was applied. The magnet is what applies the external magnetic field and the sample is placed in the middle of the magnet. The transmitter emits a frequency, which can be read and interpreted by the detector as a series of waves. Most NMR spectrometers operate from anywhere between 60 to 800 MHz, with 300-500 MHz being the most common frequencies of operation. These frequencies refer to how often the transmitter emits a signal that can be detected. The NMR spectrometer in the laboratory at our university is a Jeol 300 MHz.

Most NMR spectrometers used now are actually FT-NMRs, or pulsed Fourier transform NMRs. The pulsed Fourier transformed part of the name refers to a mathematical process that takes an oscillation vaguely resembling a sine wave and changes it into a vertical peak or series of peaks. This is what is seen on the printer and consequently what anyone who wants to know the chemical identity of the substance is interested in.

The most common atoms used with the NMR are the ¹H, ²H, ¹³C, ¹⁵N, ¹⁹F and ³¹P. In chemistry, proton (¹H) and ¹³C are most common, due to the fact that most organic molecules are primarily comprised of carbon and hydrogen molecules. The basic theory behind a proton NMR is that some protons are more shielded, or has more electron density around it, than others do, depending on what kinds of atoms they are attached to. For example, hydrogens attached to a carbon would be fairly shielded and have a lot of electron density around them compared to a hydrogen attached to a nitrogen or especially an oxygen, both of which are more electronegative than carbon. In a proton NMR, the peak of a more shielded hydrogen will show up with a lower applied magnetic field strength than that of a less shielded hydrogen. Being able to determine the chemical structure of a compound can be incredibly useful. For example, if you are trying to synthesize a certain chemical with a known NMR spectrum, you can run a sample. If the spectrum comes out looking like it should, chances are that you have made what you intended to make. The NMR can also be used in forensic work to assist in identifying an unknown substance.

Aside from chemistry, the technology seen in the FT-NMR has another application that more people have heard of. Whether someone has gone to the hospital to get the medical test done or seen a medical drama show on television, most Americans have at least heard of magnetic resonance imaging or MRI. The NMR was discovered in 1945, around the time that World War Two ended, but the MRI was not proposed until 1974 and was not put into diagnostic practice until the middle of the 1980s. Given that it is nearing the end of 2008 right now, that would date the MRI as thirty-four years of age this year, but somewhere between twenty and twenty-five years in diagnostic medicine. Despite what people may think about nuclear energy and anything else associated with things nuclear being unsafe, the MRI is a relatively safe medical procedure.

The scientific community has possessed NMR spectroscopy for more than fifty years and since then, we’ve made significant advancements. One thing that we could continue to do is to apply what we know about the FT-NMR to the MRI. If there is a possible way to make a lower dose of radiation for an MRI scan possible, research could be done in that area. Also, since an atom must have an odd mass number or an odd atomic number for the basis of the NMR to work, it would be interesting to know if any research has been done to find an analogous way to characterize atoms with even mass and atomic numbers, like sulfur and calcium. The FT-NMR has its uses, specifically in chemistry, as does the MRI in medicine.

http://www.princeton.edu/pr/pwb/98/1123/nmr.htm

http://www.wellesley.edu/Chemistry/nhk/ppt_cyano/sl_2_sciencecenter.html

http://www.cord.edu/faculty/ulnessd/legacy/fall01/andy/mri/index.htm

Halliday, David, et al. Fundamentals of Physics, Seventh Edition Extended. New Jersey: John Wiley Sons & Inc. 2005.

Mohrig, Jerry R, et al. Techniques in Organic Chemistry, Second Edition. New York: WH Freeman and Company. 2006.

Thermodynamics Lecture notes. PS-363. 07 November 2008.

NB: After I finished the paper, I couldn't remember whether L was the wavelength or the length of our physics professor's imaginary box, but it still proves that energy is quantized...
I also took out the name of the place where I go to school at and replaced it with something generic. I did actually use the school name in the paper.