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Nuclear Magnetic Radiation

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Introduction

Nuclear Magnetic Resonance Introduction Nuclear Magnetic Resonance, or NMR, is a technique used for the spectroscopic analysis of matter. A Swiss physicist named Felix Bloch developed NMR in the 1950s. NMR works by placing the substance in a strong magnetic field that affects the spin of the nuclei. Only a handful of common elements posses the property known as spin, which is essential for NMR to work. A radio wave passing through the substance repositions the nuclei. Once the wave is turned off, the nuclei release energy that contains information about the substance. This information can be translated into an image by using computer techniques. During the 1980s, NMR was seen as a useful tool for obtaining more precise images of the human body. NMR is accurate and provides doctors with a better idea of what is happening inside someone's body. The images produced are clear and concise, cutting down on the amount of radiation the patient needs to be subjected to. These images are far more accurate than those produced using ultrasonic or CAT scans. NMR is unsurpassed when taking scans of the head and neck. The clarity of images produced has resulted in an increased use of NMR techniques. As a result, NMR is now more commonly referred to as MRI (Magnetic Resonance Imaging), in order to avoid the negative connotations of the word 'Nuclear'. ...read more.

Middle

The frequency f depends on the gyromagnetic ratio, of the particle. So f = B For hydrogen, = 42.58 MHz / T. Energy Levels To understand how particles with spin behave in a magnetic field, consider a proton. The proton has a property called spin. The spin can be looked at as being a magnetic moment vector, which causes the proton to behave like a magnet with a north and south pole. When this proton is placed into a magnetic field, the spin vector aligns itself with the field. A magnet would do the same. There are low and high-energy states. The low energy configuration is where the poles are aligned at N-S-N-S. The high-energy configuration is when the poles are aligned N-N-S-S. This particle can go through a transition between the two energy levels by the absorption of a photon. A particle in the low energy configuration would have to absorb a photon to end up in the high-energy state. However, the energy of this photon must exactly match the difference between the two energy levels. The energy of a photon is related by its frequency by Planck's constant (h = 6.6 x 10-34 J s) E = h f We have seen that f = B and E = h f, therefore, if we equate the two formulae, we get a single formula that gives us the energy of the photon needed to cause a transition between energy levels. ...read more.

Conclusion

Advancements in superconducting magnet design and RF sample coil efficiency have helped to make carbon-13 spectroscopy routine on most NMR experiments. Evaluation The research was extremely enlightening. The usefulness of NMR has been highlighted to me, and I have applied my knowledge of physics to the various processes. The AS-Physics textbook gave a general overview of what NMR was, and how it worked on an atomic level. Although these descriptions were sufficient, they failed to emphasize key areas and formulae. The Longmans A-Level Physics textbook gave an insight into spin physics. The textbook gave a simple model for the spin of atoms, as well as providing a small mention of quantum theory, and how the existence of spin was discovered. Microsoft Encarta 1997 showed similar levels of detail on NMR and spin physics. The CD also gave a detailed breakdown of what spin physics entails and how it applies to NMR. The CD concentrated more on analogies and visualisations to help the understanding of the concepts, while the textbook preferred to underline the relevant physics. The images are provided by the CD. Perhaps the most helpful of the sources was a website written by Professor Joseph P. Hornak. His website outlined the specific hardware requirements and how the physics is applied to them. His descriptions of spin physics were also very visual. Although much of the material was beyond my understanding, reading the other textbooks and looking up key terms, allowed me to grasp the basic ideas being described. ...read more.

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