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An important objective of this course is to instill habits of record
keeping that will serve you well in future research. A good laboratory
notebook is essential when you begin to write papers or to develop oral
presentations summarizing your experimental efforts. A clear
well-written narrative that includes experimental schematics, plots of
raw data, and details of your analysis
methods will enable you to receive quick feedback and assistance during
lab
sessions.
You will be given a standard experimental notebook in which the
complete dated record of procedures, events, original data,
calculations and results of every experiment is to be kept. Although
you will work in a group and are
urged to collaborate on all aspects of the experiments, each student
must
keep a complete, dated record of each experiment and its analysis. High
resolution
plots, photos, and Xerox copies of shared data should be glued or taped
in
place.
Your notebook will be checked during class times several times a
semester.
The following is a list of record keeping guidelines to follow when
performing laboratory work.
- Create a descriptive table of contents
and
make an entry every time you add new material.Title the TOC with the
following: Date - Contents - Page. Don't use generic entries like \Day
1" or \Analysis". Instead, produce records of signifcant mile stones:
e.g. \Calibration of NaI
ScintillationCounter Using Ba-133 and Na-22 Check Sources",
- Sign and date every page demonstrating
authenticity.
- Don't erase, use white-out, or tear out
pages of a lab notebook. Indicate \mistakes" by simply drawing a
single, neat line through the item. These may prove to not so incorrect
as initially thought and will very often be useful as a guide to how
the experiment was done and provide clues on how to better execute the
experiment next time.
- Loose-leaf pages are not acceptable
within
a lab notebook. Graphics or tables generated by computer must be neatly
taped into the notebook. Remember to annotate these types of graphics
with as much information about how they were created as possible.
- Your notebook should contain diagrams,
narratives, tables of raw data, formulas, computations, reduced data,
error analysis
and conclusions in a neat compact, orderly arrangement.
- Bring your notebook to every lab session.
Failure
to do so will result in penalties to your grade.
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- Preparing for an
experiment
o Prior to
each
new experiment read the experimental
writeup thoroughly in order to understand the physics
involved.
Do not start an experiment before understanding the entire procedure.
o Preparatory
questions. Each lab guide includes a
set of preparatory questions which point you to the essentials of the
experiment. Work out the solutions to these problems in your lab book before starting the experiment.
Make a
copy of your solutions and hand to the TA no later than the beginning
of the second session. Late
solutions will not be accepted because you will need to know this
material BEFORE the experiment.
o Summary
of objectives and procedures. The next
entry in your lab book should be a statement in your own words of the
essential physics ideas and principles of the
experiment. List your experimental objectives and how they
relate to the essential physics. After listing the objectives,
identify
the things you will have to do, the data you must obtain and identify
the
required calibrations.
o Your l aboratory notebook should be with you
at all times and used to keep a record of every step of the
experiment. It must contain sufficient narrative as the
experiment proceeds so that, years later, you could reproduce the
results
you obtained. Notes, tables, and graphs should be neat and compact,
leaving
as little empty space in the lab notebook as is compatible with clarity
and
the logic of organization. There should be no loose sheets or graphs in
your
notebook.
o On the first day of a new experiment , before turning
on
any of piece of equipment, read the manual and familiarize
yourself
with the controls and operation. The relevant manuals will be
placed
near each experiment. If you cannot find a manual ask the course
assitant
to help you find it.
o When you feel confident you understand the equipment and
the
measurement procedure hook up the experiment according to the
diagram
described in the lab writeup and turn on the the equipment.
o At this point sketch a block diagram of the apparatus and
signal chain in your lab notebook.
o Note typical “readings" and instrumental settings
so as to be able to quickly setup an experiment on subsequent days.
o Sketch waveforms at various places within the
signal chain. This will help ensure your understanding of each
component and permit you to rapidly identify equipment failure.
o When tabulating data into columns, use headings and list the
units
and estimated measurement uncertainties.
o Don't wait until after the session has ended to
visually examine the quality of your data. Create hand drawn
plots of data, as
they are acquired, not later. These initial plots will save you time
and frustration
in making sure that your data are reasonable and suggestive of the
behavior
you expect. Analyze data in the lab in a preliminary way as you go
along
to check for reasonableness. If you are making a series of measurements
of
one quantity as you vary another, plot the results as you go along so
that
you can see the trend, catch blunders, and judge where you may need
more
or less data. Repeat every measurement at least five times in
as independent
a manner as possible in order to establish a statistical basis for
estimating
random error and to reduce the chance of blunders. If you get through
all
the manipulations and preliminary analysis of an experiment in less
than
the alloted time, take the opportunity to perfect part or all of the
experiment
so as to obtain the best possible data set.
o Some experiments will require you to transfer your
data to a computer and store them in files on disk. Obviously, it is
not
practical in these cases to print out all your data and paste them into
your
notebook. However, your lab notebook should include a clear description
and
summary of the data files so that when you return to them days or weeks
later,
you are able to identify particular files with procedures you carried
out
in the lab. Identify the location of large data files or long analysis
programs if they are too big to directly enter or tape into your
notebook. Analysis scripts, functional forms for non-linear fits, etc.
should always be present in your notebooks.
o Your notebook will be checked and graded
during class.
o As a courtesy to the next group leave your work area
at least as tidy as you found it. Return reference
material and tools at the end of each lab.
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Computational
resources
We have several Windows XP
machines in the lab with data analysis programs including Origin (the manual
can be downloaded here
an example can be found here)
Kaleidograph
and Excell (an example can be found here).
Mat lab can be found on Rutgers machines in most computer
labs.
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The lab report should show mastery of the entire experiment, and
possess a neat appearance with concise and correct English. It must be
typed on 8 pages or less (excluding the title page bibliography
and supplementary information)
with double spacing and 12 pt font. (If you wish, you may
attach
data
sheets for your own records.) Alternative if use PRL or Nature
format (two column and single spaced) it should be ~ 4 pages. The
report should consist of the
following elements:
I. Abstract
II. Introduction (purpose, equations; 1 ~ 2 paragraphs)
III. Apparatus (1 paragraph of description)
IV. Data (pages from the student's lab notebook)
V. Analysis and Results (graphs, calculations, answers)
VI. Discussion (measurement uncertainties) and Conclusions
VII Bibliography
ABSTRACT should appear on the title page. This is part of title page of
the report, but it is a good idea to write it last, when you know
exactly what you are summarizing. The abstract is a concise summary of
what the reader will find in the paper. It should briefly mention the
motivation, the method and most important, the quantitative result with
errors. Based on those, a conclusion may be drawn. You
should use appropriate technical terms, leaving their definitions and
explanations for the Introduction.
INTRODUCTION OR BACKGROUND. Desctibe briefly what the experiment
is about: Give some historical context, but not many pages or long
quotations. Outline theoretical results which will be needed, but omit
intermediate steps of derivations; you don't have to tell everything
you know. Be sure to define all terms appearing in formulas.
Material and ideas drawn from the
work of others must be properly cited in the bibliography.
APPARATUS AND PROCEDURE. This section describes the main components of
the apparatus. It makes reference to a figure(s) which contains a
diagram of the apparatus and includes the most important signal
processing steps. The figure should be referenced as early as possible
in this section with the placement of the figure as close to the
descriptive text as is possible. This should be followed by a
description of the procedures and of the measurements.
DATA. Give a narrative, which cites data in tables and graphs. All
figures and tables should be numbered, and should have captions.
Make sure that axes are labeled, with units. The text should tie
everything together in a linear sequence. Therefore all Tables,
Figures, and Graphs should be cited by number at an appropriate place
in the text. Place Figures, Graphs, and Tables in the text as close as
possible to where they are cited (rather than at the end of the
report). Do not inundate the reader with material;
you should find a way to summarize your results in two or three
plots
or tables.
ANALYSIS Compute from your data whatever quantities are most
appropriate for making comparison with theory, or for extracting useful
information. Where
repetitive calculations are necessary, present one sample calculation
to
make the procedure clear. Be sure to include a precision (i.e., "error"
analysis),
which starts from estimates of the uncertainties of the measured
quantities
and leads to an estimate of the precision in the final quantity derived
[See
any of the references on statistics and error analysis]. Remember that
the
crux of the report is how much you can get out of your measurements and
how
reliable the results are.
CONCLUSIONS. State the main results, but omit vague generalities. List
and discuss possible causes of any discrepancies between your
experiment and theory
or previous measurements; bring your estimate of precision into the
discussion.
You might suggest specific improvements of the experiment.
BIBLIOGRAPHY. In this section which should be after the
last page list all references used, whether explicitly cited in the
text or not. Use citations throughout the paper to acknowledge sources.
These citations may be by number or by author.
Comments .
It may be useful to model your reports on Nature letters or
Physical Review Letters (some copies are reserved in the lab).
Reports will be graded using the following criteria:
1. Theoretical and/or Experimental Motivation - 10%
2. Description of Experiment - 40%
3. Analysis of Data and Results - 40%
4. Style and English - 10%
5. A 4% deduction will be assessed for EACH day the report is late.
INSTRUCTIONS FOR
ORAL
PRESENTATIONS
A tutorial on writin
g Powerpoint presentations can be downloaded
here.
At the end of the
term, each student will give a public oral presentation
which will be attended by all
students in the section. The presentations should be in the style
of a paper presented at a conference.
Questions from classmates are encouraged allowing for a general
discussion
of the experiment.
Guidelines
- The
presentation
should be about your fourth experiment, unless a substitution is agreed
upon
with the instructor.
- All
students should attend the whole session, and participate in asking
questions.
- Each
lab partner will have 12-15 minutes to make a presentation, with a few
minutes after each part for questions (such as requesting
clarification). There will
be time for questions addressed to either partner after their talks.
Partners
should decide between themselves how to divide the material
(Background,
theory, apparatus, procedure, data, analysis, conclusions, etc.).
However,
each should give a single segment.
- The
talk should be prepared for a powerpoint
presentation. It should include title page, outline of talk, graphs,
diagrams,
summary of conclusions, etc.. Do not include
extensive
text or long derivations of equations, but just outlines, final
equations,
or a few sentences of conclusions. The blackboard is also available.
- Practice
the talks with your lab partners. In addition to refining the
presentation, checking the length, and making sure nothing crucial
falls through the cracks, try to anticipate
questions which may be raised.
- Each
student should ask at least two questions (overall) of other speakers
(besides lab
partner). These should not be confrontational, but seek clarification
of
surprising, intriguing, or unclear points
in the
presentation.
- Useful
links and examples
Tutorials
on basic measurement apparatus
References on Statistics
and Error analysis
Safety
Prevention of injury is a
matter of being aware of pieces of equipment
that are potentially dangerous. Since it is virtually
impossible to set up a reasonably comprehensive and interesting set of
experiments in modern physics without using equipment which has
potential hazards, it is essential to be aware of
the hazards, and exercise appropriate precautions.
Electrical Safety
The first rule is never to work alone. All high voltage supplies are
clearly marked as dangerous. Do not poke or probe into them. Turn off
the supply if you need to change cable connections. The supply may be
dangerous even when turned off if the capacitors have not discharged;
always keep one hand in your pocket when testing any circuit in which
there may be high voltages present so that if you get a shock, it will
notbe across your chest. Never go barefoot in the lab. Remember that it
is current that kills. A good (e.g. sweaty) connection of 6 volts
across your body can kill as well as a poor connection of 600 or 6000
volts.
Laser Safety
A laser beam may not seem very bright, but if it enters your eye it
will be focused by the lens of your eye to a pinpoint spot on the
retina where the intensity is sufficient to destroy retinal cells. It
is wise to terminate a laser beam with a diffuse absorber so that the
beam doesn’t shine around the room. Never examine the performance of an
optical system with a laser by viewing the beam directly with your eye
or reflector.
Radiation Safety - link to power point
presentation
Ionizing radiation damages tissue; any exposure should therefore be
minimized. The unit of radiation exposure is the rem (roentgen
equivalent man). Your inescapable dosage from cosmic rays and other
background sources is 360 mrem yr−1, which works out to 4.2 x 10−2 mrem
hr−1. The recommended limit to controllable exposure for a member of
the general public is 100 mrem yr−1, averaged over any consecutive five
years. If you follow the Lab guidelines, your exposure will be
only a small fraction of the dose you receive from the natural
background.
Radioactive sources emit three types of radiation: high energy helium
nuclei (alpha rays), electrons (beta rays), or photons (gamma rays).
Most of the sources in the Modern Physics Lab emit only gamma
radiation.
The strength of a radioactive source is measured in curies (Ci).
A one-curie source has an activity of 3.7 x 1010 disintegrations s−1.
The “absorbed dose” is a quantity that measures the total energy
absorbed per unit mass; it is measured in rads, where 1 rad = 100 erg
g−1. The “equivalent dose” is measured in the units discussed above,
the rem. The equivalent dose is derived from the absorbed dose by
multiplying by a “radiation weighting factor” which is a measure of how
damaging a particular type
of radiation is to biological tissue. For photons (gamma rays) and
electrons and positrons (beta particles), the radiation weighting
factor is unity; for helium nuclei
(alpha particles), it is 20; for protons with energy greater than 2 Mev
it is 5; and for neutrons it ranges from 5 to 20, depending on the
energy. When you use the meter in the lab, the readings are in rads,
and you must consider the type of particle when you work out the
equivalent dose.
For gamma rays with energy greater than 1 MeV, a useful approximation
is that the equivalent dose due to a source with an activity of C
microcuries is 5.2 x 10−4CE R−2 mrem hr−1, where R is the distance from
the source in meters and E is the energy of the gamma ray in MeV.
For gamma rays with energy less than 1 MeV, this formula is still
approximately true for a full body dose. However, low-energy gamma rays
deposit their energy in a smaller mass of tissue than high-energy gamma
rays and can cause high local doses. For example, the local dose to the
hands from handling a 10 keV source can be up to 25 times the value
given by the above formula; hands, however, have a higher tolerance to
radiation
than inner organs or eyes.
The protective value of shielding varies drastically with the energy of
the photons. The intensity of a “soft” Xray beam of < 1 keV can be
reduced by many orders of magnitude with a millimeter of aluminum while
1.2 MeVgamma rays from 60Co are attenuated by only a factor of 2 by a
lead sheet one-half of an inch thick. The best
way to keep your dosage down is to put distance between you and the
source. If you stay a meter away from most sources in the Lab, you will
be receiving, even without any lead shielding, a dose which is much
less than your allowable background dose. If, however, you sit reading
the write-up with a box of sources a few inches away, you may
momentarily be receiving ten to a hundred times the background level.
Precautions for Working with Radioactive Materials - ALARA
1. Don’t handle radioactive sources any more than you have to.
2. Work quickly when transferring or positioning radioactive sources.
3. Never take a source out of the Lab, even temporarily.
4. Keep sources away from your body.
5. Be aware of the sources being used in neighboring experiments.
6. Remember ALARA – As Low as Reasonably Achievable!
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