This article, authored by Professor Don Treacy, appeared in the USNA Trident newspaper - Friday 11 Aug. 1995.
Toadfish, meteors, lead coffins and midshipmen's class rings have something in common: they are all test subjects in the Naval Academy Tandem Accelerator Laboratory (NATALY). Although these are very diverse samples, they all are subjects of investigation in particle beam accelerator located in the basement of Michelson Hall. The stories behind this collection of samples, as well as some other very strange pieces, are fascinating.
The facility is a tandem accelerator where protons and other atomic particles are accelerated to very high speeds and then slammed into targets of interest to obtain information useful to ecologists, cosmologists, historians and midshipmen. Protons are the particle of choice for many of these experiments. The protons can be accelerated to approximately one-tenth of the speed of light and directed toward these targets. When they hit the target they can strip electrons from the target atoms or excite their nuclei. When they remove electrons from the target atoms the liberated electrons will recombine with the stripped atoms. During this recombination they emit x-rays which are a fingerprint of the atoms with which they recombine. If these x-rays are detected and analyzed they will tell us what kind of atoms are in the target. This technique is called particle-induced x-ray emission (PIXE) and is the basis for many of the studies done at NATALY.
Now that you aware of most of the physics involved in the experiments, you can understand why many of these things are considered interesting. Midshipmen rountinely use their class rings as targets to determine how much gold is contained in the rings and identify other metals present. Ask the midshipmen who have done this as part of their Physics of the Atom course and you will discover that it is more involved than merely determining if the ring manufacturer gave them the proper amount of gold.
Why would midshipmen ever try to determine which elements are present in a meteor? The answer to this question (really which isotopes of which elements are present, and in what proportion are these isotopes present) will tell them about how the solar system originated and how it is evolving. This is a critical piece of information for many models of how stars develop. And while we are investigating meteors we may mention that core samples from about 1200 feet under the Chesapeake Bay may give us information about how and when the bay was formed. If a high concentration of the element iradium is found at some particular depth in a core sample then it is likely that a meteor slammed into the area at the time at which that sediment was forming. Information about how widespread the iradium is may indicate the size of the meteor. This topic has been examined at NATALY.
Ecology and marine environment students can look at oysters, their shells and oyster toadfish. Oysters filter water and deposit elements which are contained in that water in their organs. If these organs are irradiated with a particle beam they can indicate what the water conditions were where they grew. A comparison of oysters from different parts of the Bay can alert us to the varying conditions in which the oysters grew. The story for toadfish is very similar except that they concentrate slightly different elements and they are slightly more mobile than the oysters. Another piece in this environmental puzzle is the oyster shell which, unlike the oyster, stays around for a long time. This makes it possible to compare shells from oysters which lived a thousand years ago with shells from today's oysters in an attempt to determine how the Bay is changing over long periods of time.
Budding archeologists can have their fun with PIXE also. Artifacts taken from St. Mary's City can give us a glimpse of how the early settlers lived. The most famous sample of this type studied at NATALY is lead from coffins used to bury some of the early settlers. By determining the proportions of various metals in these lead coffins it can be ascertained if they were imported from England. If they were imported the person buried was probably from a wealthy family and this information can help identify the person buried. The bricks from the early homes have their own story to tell. How did the original settlers make their bricks? How many brickmakers were there in the early settlement? An elemental analysis of the bricks can shed light on these questions. The same is true of the pottery found at St. Mary's City. Many of the ceramic pieces can be attributed to individual potters by the way they mixed their clay. The mix of elements is different for each mixing recipe and these mixes are identified using PIXE. If we wish to go a bit further back in history we can examine some of the arrow heads found in Indian camping sites which have been abandoned for centuries. The object of the game here is to determine the type of stone used to make the arrow head. Depending upon what type of stone was used the origin of these projectile points can be determined, sometimes almost to an individual quarry. In turn this tells the archeologist about the tribes which traded with each other and the frequency of this trading. Accelerating protons can help build a picture of early American commerce.
A special mention should be given to work being done on the remains of HMS deBraake. This ship had a colorful history before sinking off of Cape Henlopen in Delaware in the late 1700s. The focus of interest here is the metal fasteners used in the ship. The British Admiralty was trying new methods of refitting ships to minimize galvanic action (corrosion) at the time. The condition of the spikes and other fasteners gives a clear picture of the state of the art in corrosion prevention at that time. The breadth of fields which can be studied using the elemental analysis PIXE is amazingly rich.
Who does these novel experiments? For the most part they are done by midshipmen under the direction of members of the Physics and Oceonography Departments. Many midshipmen from the Physics Department and the Oceanography Department have participated in these investigations over the years. The facility is used in three physics courses, in 490 projects and by several Trident Scholars. The experiments are performed, the data is saved analyzed and the results are published. The educational experience gained by midshipmen has served them well. The comments which come back to the Academy on their performances after graduation are all very positive. These mids are exceptionally active; there are "no lazy midshipmen" who have been in the program. They have exceptional problem solving skills and are recognized as being good members of a team. The educational experience gained from working in the Naval Academy Tandem Accelerator Laboratory is full and rewarding for those students who are willing to put something of themselves into it.
Last updated 2003 April 21 by Paul Mikulski, mikulski@usna.edu