[ATM] magnetic resonance spectrometer

[Guy Brandenburg]

Here is the first part of the chapter on making your own magnetic resonance spectrometer. My Optical Character Recognition program in my Epson Smart Panel is acting quite weird, which is why I only hve done the first three pages or so. Is there interest in proceeding?

Guy
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  A SIMPLE MAGNETIC-RESONANCE SPECTROMETER  At the center of every atom there is a minute top -- the nucleus, which spins on its axis with incredible speed. By subjecting it to crossed magnetic fields that pulsate you can flip it over, make it wobble and, by these effects, identify itself. Here is a simple apparatus for thus experimenting with the nucleus. It was especially designed for amateurs by scientists of the U.S. Air Force
   
  SHORTLY AFTER WORLD WAR II a group of physicists wrapped a coil of wire around a glass tube in which water had been sealed, put the assembly between the poles of a magnet and sent a high-frequency current through the coil. When the frequency was raised or lowered through a critical range, the current flowing in the coil vaned sharply. This occurred precisely at the point where the frequency of the oscillating magnetic field set up by the coil resonated with the magnetized nuclei of hydrogen atoms in the water.
   
  Further experiment showed that other atoms as well as molecules of many kinds react in the same way. Of more interest, however, was the observation that the current varies uniquely for each kind of substance sensitive to the test. In the dozen years since these relatively simple experiments were made the technique has given rise to an instrument called the magnetic-resonance spectrometer which rivals the power of the optical spectroscope for investigating the structure of matter.
   
  In the course of applying the new technique to the analysis of biological substances, a group working under Miles A. McLennan in the Bioelectronics Section of the Aero Medical Laboratory at the Wright  Air Development  Center has designed a simple version of the magnetic-resonance spectrometer that amateurs can make at home. It should serve not only as an introduction to an interesting new field of experimental physics but should also make an attractive classroom demonstration or science-fair project.
   
  According to the "classical" theory of physics, all elementary particles of matter spin on their axes like tops, and those that have an electric charge {e.g., electrons and protons) generate magnetic fields. (The classical picture has now been superseded by the quantum-mechanical view, but it will suffice for the purposes of this discussion.) Particles bound in atoms and in molecules not only spin but also move on orbits. This motion adds to the field generated by the spin. The fields of neighboring particles merge; depending on the structure of the atoms or molecules and on the direction in which the magnetic forces point, the fields tend to cancel in some cases and to reinforce in others. In consequence all atoms and molecules are characterized by unique patterns of interacting magnetic forces.
   
  What will happen to these tiny magnets if they are subjected to the influence of an external magnetic field? It was this question that led to the development of the new technique. In the case of the single-proton nuclei of the hydrogen atoms of water, the magnetic axes normally point in random directions. It might therefore be supposed that an external field would cause the proton axes to line up in the direction of the field. This, however, does not happen. Instead the field causes the protons to precess, or wobble like a spinning top that has been tipped from the vertical. We might say that each particle now has two axes; it spins on one and processes around the other. The axes on which the particles precess line up with the external field, but attempts to align the axes on which they spin get nowhere. Increasing the strength of the external field merely causes the particles to process faster.
   
  In fact, the rate of precession varies in proportion to the field strength and is equal to the intensity of the field (expressed in gauss) multiplied by 4,228.5. Thus when a sample of water is laced between the pole, of  a typical magnetron magnet with a field strength of 1,450 gauss, the hydrogen nuclei precess at the rate of 6,131,325 revolutions per second. 
  It is possible to disturb the particles, however. They can even be flipped over so their “north” and “south” poles are reversed. 
   
   
   
   
  


"Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved."
- wrote Charles Darwin.
Guy Brandenburg, Washington, DC
My home page on astronomy, mathematics, education:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
or else 
http://tinyurl.com/r6fh2