The object of this course is to give students an in-depth experience in experimental physics so that they can understand how laboratory measurements test concepts in physics. There are thirteen experiments of varying difficulty. Support facilities make it possible to extend and modify the individual experiments. From literature references students are expected to design their experiments, assemble and perhaps partially construct the apparatus, and report on the results in the form of a technical paper.
We hope that this experience will give you some insight into what it is that an experimental physicist does. We also hope that from it you will begin to develop a proper respect for measurements, seeing them as neither sacrosanct nor ignorable at will. Finally, we expect that you will improve your record-keeping skills and your ability to give a coherent, readable account of the work you have done according to a previously arranged and fixed schedule.
Were one to ask a number of experimental physicists what techniques they considered to be most useful in their research, almost all would mention machine shop practice, electronics techniques, and digital computer programming. Some would list, in addition, high voltage techniques, microwave techniques, cryogenics, high vacuum technology, and optics. It is not possible to learn all of these techniques during the semester, but in the time available some will be learned while performing the experiments.
The future theorist has here the opportunity to get first-hand knowledge of the world of your future experimental colleagues and to explore the experimental aspects and techniques of the field into which he intends to go. Experimentalists will learn some physics and useful experimental methods.
Emphasis is on independent work. This implies that students should be able to demonstrate to the instructor's satisfaction the actual set-up and operation of the experiments.
The following should receive careful consideration:
. The physics to be studied in the experiment, the quantities to be measured, and the principles of the methods needed.
. Before data taking: thorough understanding of the characteristics of all components of the experiment; the arrangement of the apparatus (physical dimensions, wiring, etc.); and the nature of data to be taken.
. In data evaluation and analysis: a study of the factors, both statistical and systematic, that limit the accuracy of the experiment. For example, there is no point in using a complicated fitting program to locate a peak energy to 0.05% if residual uncertainties due to drift exceeds 2%. This should be considered at every phase of the experiment.
. At the conclusion: the significance of your experiment in relation to its field and, if possible, to physics in general.
. The number of experiments students are required to do is two in both PHYS 621 and PHYS 429.
. Each experiment should be selected in consultation with the instructor. The student is encouraged to select experiments in different fields, in the hope that one (or all!) may be found to be of sufficient interest to merit further study at some later time. There will be regular discussions with the instructor during the course of the experiments. Attendance for all six hours of the scheduled laboratory session is mandatory. It is important to note, however, that in addition to the time spent in the lab, an almost equal amount should be spent in study and planning. Attendance is required in order to provide regular contact between students and the staff, so that students receive all necessary assistance. Additional time in the lab beyond the prescribed hours can be arranged with the approval of the teaching assistant or the instructor and through the Laboratory Coordinator.
. The specific requirements of the course are:
. Notebook: It is not possible to remember completely all the information on an experiment nor to memorize selectively the important facts and data for final consideration. What was seemingly an unimportant observation may prove to be crucial in the final analysis. Therefore, you must have and use a laboratory notebook as a research journal (diary). The style should be such that it would be possible for you to go back to your notebook six months later and understand its content. Entries should be dated and kept in date order (leave no blank pages). Entries should be in ink, not pencil. Design considerations, preliminary calculations, studies of theory, preliminary results, tests of components, and, above all, the final data, must be entered in some detail at the time of observation or study; records of mistakes must not be destroyed. Data in the form of print-outs, photographs, or recorder charts should be attached so as not to fall out. This procedure is practiced by most experimentalists and is required of students in the Graduate Laboratory. The recommended type is S.E. & M. Vernon No. 89.
. Experiment Selection: Before starting an experiment, students should discuss with the instructor the physical phenomenon to be studied and the means of carrying out the study. This discussion will cover a simple summary of the basic physics, a discussion of the set-up to be used, order of magnitude estimates of the quantities to be measured, and the major sources of error that influence the results. This is an open discussion of the essential elements of the experiment.
. Experiment: Students are expected to set-up and understand the equipment used in the experiments. This includes knowing about the appearance and meaning of the signals at all stages of the set-up. Students should be prepared to demonstrate their understanding to the instructor during the course of their performance of the experiment.
. Progress: Students will meet regularly with the professor during the course of the experiments. This is to ensure that reasonable progress is being made in carrying out the experiment, to assess the direction the experiment is taking, and to address problems that may be hindering completion of the experiment.
. Report: The style should follow that of papers in the American Journal of Physics. You should consider your paper as a presentation to your peers in the physics community of new experimental results. The tone of this paper should be that of the experimental physicist who has performed an experiment, and is making the results available to the scientific community. It is important to compare results with published results. Disagreements with simple theory or other results should be discussed in light of experimental technique and uncertainty, as well as potential higher order theories. Often the small, but statistically significant, "bump" is the most interesting part of the experiment. Details that would distract the reader from the clear and convincing presentation of your experimental results but which you feel should be presented can be included in appendices. This report should be prepared using a word processor capable of displaying equations and symbols or formatter such as Tex. The manuscript format should follow directions in the American Institute of Physics AIP Style Manual, 4th Edition (1990). Figures and tables should be numbered and so cited in the text to permit the reader to understand the point which they support. Figures and tables should be described fully, both in the text as well as in the captions. References and tables should follow the AIP format. The manuscript format should follow that of a paper submitted to the editor of a journal. It is double spaced with wide margins (> 2.5 cm) for editing notes and comments by "reviewers." The figures are full sized, one to a page and placed at the end. The order of the pages is given on page 1 of the Style Manual. At the end of each experiment, during the last class before the date on which reports are due, students must present a final draft of their report to a peer reviewer and make constructive comments and suggestions concerning the content and the format of the report he/she reviewed. Students will have time to make changes to the final report. On the date reports are due, laboratory notebooks will be handed in as well. The draft copy with the annotations and comments of the peer reviewer must be turned in as well; it will be regarded as part of the reviewer's performance. There will be a 15-30 minute oral discussion of the paper and a defense of the results with the instructor. Students may be asked to demonstrate their experimental set-up as part of the discussion.
. Schedule: Students should have appropriate time scheduled for the carrying out of their experiments and the writing of their reports. Experiments and reports are required to be completed by specific deadlines.
. Facilities: The facilities available in performing experiments are described in Section, Laboratory Facilities. Note the restrictions indicated; these are consistent with those in any modern laboratory. The Coordinator, graduate assistant, and instructor are here to assist you in performing experiments.
. PHYS 429 meets concurrently with PHYS 621 for a scheduled 5 hours per week instead of the 6 hours for PHYS 621.
. Although the courses meet concurrently, the standards for grading are different in the two courses. In particular, an undergraduate student is not expected to have the theoretical sophistication of the graduate student.
. All of the facilities of the laboratory are available for student use.
. Copies of some books and most journal articles referenced in this handbook are available in room PHY-3333. The remaining reference material may be found in the Engineering and Physical Sciences Library. The "Operation" portions of equipment manuals are also available. This material is for use in the laboratory only and must not be removed from the laboratory area. Please return all reference materials to their respective files. These reference materials are part of the Graduate Laboratory's inventory. They are not to become part of the student's reference library.
. Soldering irons as well as a selection of small hand tools are available for use in the laboratory. For more involved work the department has a student machine shop in Room PHY-0125. Mr. Russell Wood, a skilled and patient teacher, is the supervisor and will be pleased to answer questions and give advice. It is necessary to see him before initiating any project in the student shop. For reasons of safety unsupervised work in the shop is not permitted. Plastic and metal supplies are available in the student shop and in the main shop stockroom.
. Modular nuclear instrumentation is stored in Room PHY-3323, as are all radioactive materials. Radiation monitoring film badges are stored in the gray wall cabinet in Room PHY-3333 and must be returned there when not in use. These personal radiation monitors must be worn at all times when in Room PHY-3323 or when using any radioactive materials. Radiation badge reports will be sent directly to the badge-holders.
. Most of the instruments and expendable supplies stocked by the laboratory are stored in Room PHY-3313. Unlike most teaching laboratories, we grant students self-service privileges in our stockroom. It is assumed that you will return all equipment or supplies to their proper places of storage when finished with them. The purpose of returning equipment is to save the time and energy spent searching for needed equipment or supplies. Students are the chief beneficiaries of this policy. Those who do not abide by it will be blacklisted and will lose the self-service privilege.
. Expendables and other small items not available in the laboratory may be obtained at the physics store and chemistry store (CHM-0202) with a pick-up authorization available from the Laboratory Coordinator.
. Out-of-hours work is permitted subject to safety restrictions. You may sign out a card-key to the room you must use beyond the end of the working day. Keys must be returned at the end of the semester. In any case they will be disabled at semester's end. After-hours work with power tools by unsupervised students is strictly forbidden. Permission is never given for unsupervised work in the radiation area (PHY-3323).
. If you read the manual before you use the instruments there is an excellent chance that you will find an easier way to do the job. Most instruments are more versatile than is generally recognized; e. g., the operating sections of many manuals have application notes. Do not hesitate to use a superior instrument, if available, just because it is not a standard one for the experiment. On the other hand, don't use a more complicated instrument than you need.
. Apparatus will be secured and experiments may be dismantled (because of equipment sharing) at the end of the day, unless prior arrangements are made. If you make such an arrangement, put a big sign on the apparatus, or someone may assume that the experiment is free. Loose papers and other "unidentifiable objects" may be discarded.
. Read the manual before using any instrument for the first time. These manuals are found in the Graduate Laboratory Library, Room PHY-3333, in the files labeled "Manuals".
. Most electronic instruments can be easily damaged by excessive voltage or current. Excessive voltage can be as low as 7 volts for some instruments.
. There are mechanical vacuum pumps in the laboratory. They should never be turned off and left with a vacuum at the pump intake port because oil may be drawn into the system. They may be left on overnight, but not pumping at atmospheric pressure.
. Oil diffusion pumps are easily damaged and very tedious to clean. Exposure to air results in either cracked or oxidized pump oil, which can be a tarry mess. Read the manual for the system very carefully.
. Photomultiplier tubes exposed to light become noisy and remain so for an extended period. Photomultiplier tubes exposed to light with accelerating voltage applied are instantly destroyed.
. The heat of vaporization of helium is a very small, 6 cal/gm. By comparison, that of water is 596 cal/gm and that of nitrogen is 93 cal/gm. For this reason helium transfers will only be done by the staff.
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