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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 Scintillation Counter 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 Excel (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. Length should be ~
3200
words (excluding the title
page bibliography and supplementary information in appendix ). This
corresponds to ~ 8 pages with double spacing and 12
pt font. (If you wish, you may attach data sheets for
your own records.)
Alternative if you chose PRL or Nature format it should be ~ 4 pages
(two
column 10pt font and single spaced). 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 - 15%
2. Description of Experiment - 15%
3. Data presentation and Analysis - 40%
4. Conclusions and answers to questions 20%
5. Style and English - 10%
6. 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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