Nuclear Magnetic Radiation

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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'. In fact, NMR does not involve any form of radioactivity or ionising radiation. The word 'nuclear' was used to imply the manipulation of small atoms. Subsequently, the medical world has shed the term NMR, and has developed new techniques, which are based on the principles first established by Bloch.

Most matter examined by NMR consists of molecules. Molecules are composed of atoms. For example, a water molecule contains two hydrogen atoms and one oxygen atom. A single hydrogen atom is made up of one proton. This proton possesses a special property known as 'spin'. Spin in an atom can be thought of as a small magnetic field surrounding it. This magnetic field will cause the nucleus to produce the essential NMR signal.

I chose to research into medical physics, as it is a field in which I have little knowledge. Learning things from first principles would give me the opportunity to provide a report from a different perspective. I feel I have been given an opportunity to expand and to learn new ideas, which I wouldn't have been able to do had I chosen a topic, which was familiar to me. Knowing nothing about my chosen topic is like an artist starting work with a blank canvas, as opposed to starting with a half drawn picture.
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My aim is to explain the principles behind NMR, and to investigate the underlying physics, which make NMR such a useful tool to the medical world.

Spin Physics

Spin is referred to as angular momentum. There are two types of angular momentum: spin and orbital angular momentum. Spin is a fundamental property of elementary particles. Orbital angular momentum results from the motion of a particle. An electron inside an atom has orbital angular momentum, and spin angular momentum.

The Dutch physicists Samuel Abraham Goudsmit and George Eugene Uhlenbeck first suggested the existence of spin ...

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