Physics 405, Spring 2003
Last updated
04/30/03
Helpful Hints, corrections, etc.
Here is a link to the NIST Reference
on Constants, Units and Uncertainty .
You may find this useful in analyzing your data. This is the last word
on how to
properly quote uncertainties in your measurements.
Experiment I: Measurement
of the Speed of
Light
- hints on laser alignment
- Don't look through the eyepiece unless the rotating mirror is ON.
- There is significant backlash in the vernier - think about how to
take all your data while turning the vernier only in one direction.
Experiment II: Experimental
Atomic
Spectroscopy
- Optimizing the slit widths for the best resolution is best done
with the H/D source.
- Turn the flourescent lights off when you are making a scan to cut
down on the electrical noise coming from the lights.
- Don't forget to calibrate the display on the microprocessor
against the dial indicator on the monochrometer. If you don't, you may
run the monochrometer into either its upper or lower limit. If this
happens, contact one of the instructors right away so it can be reset.
Experiment III: The Franck-Hertz Experiment
- Give yourself a quick refresher on RC circuits for oscillating
signals before connecting the electronics.
- REMOVE THE RC FILTER WHEN YOU CALIBRATE THE 40V POWER SUPPLY!
- Allen suggests turning off the temperature controller just before
taking a scan with ACQUIRE (don't forget to turn it back on though.).
- Simultaneously recording the Franck-Hertz tube current in channel
0 and the ramping voltage in channel 1 is tricky. The ramping power
supply is floated away from ground by the retarding voltage. I
suggest measuring from ground to the filament, this measures the sum of
the retarding voltage and the ramp voltage.
- Think hard about how to fit the peaks, and how to "normalize" the
curve to correct for the fact that the overall current rises with the
accelerating voltage.
Experiment IV: Determining
Planck's Constant
- Take a look at the plot of intensity
vs wavelength to find the best peaks to look at.
- Give yourself a quick refresher on RC circuits for oscillating
signals before connecting the electronics.
- You might be interested in taking a look at this recent
measurement of Planck's constant at NIST in Gaithersburg, MD. See
the associated article (21 Sep 98) by E.R. Williams, et al., Phys. Rev.
Lett. Vol 81, (1998) 2404.
- Look at Melissinos (p. 24) for suggestions on how to analyze the
data to find the stopping voltage. Think about this - other
methods may work even better!
Experiment V:
Experiment VI: Measurement
of (e/m) for the
electron
- You MUST go over the operation of the vacuum system with either
Allen Monroe, Tom Baldwin, or one of the instructors before starting
the experiment! See also Appendix A in the lab manual.
- Here's a
calibration from 1996, plus a plot showing the residual
errors. Refitting this data (2003) shows the
uncertainties: intercept tof (0.250 +/-0.009) G and the slope of
(47.3 +/- 0.1) G/Amp. This whole calibration needs to be redone
with a stable series resistor for measuring the current.
- Think about the contribution of the earth's field to your
measurement, and how you can account for (or get rid of) it.
- See the updated instructions
for operating the vacuum system, replaces Section III of Appendix A.
Experiment VII:
Introduction to Nuclear
Spectroscopy I
- NOTE: this experiment along with VIII and IX use a data
acquisition and software package specifically designed for
nuclear spectroscopy. You should take a little time to familiarize
yourself with the program before attempting to take data. See Appendix
C for a brief description of the program.
- For this experiment, and also exps VIII and IX, here is a brief
description on using either the Tektronix
2245A or the digital Tektronix
TDS360 scopes.
Experiment VIII:
Introduction to Nuclear
Spectroscopy II
- See the notes in exp VII regarding data acquisition.
- You can find more and up-to-date information about the particular
nuclei you are studying at the National
Nuclear Data Center at Brookhaven National Lab. This
picture of the 56Mn->56Fe
gamma ray scheme was generated using the MIRD database. Also, take
a look at the 228Th spectrum hanging on the wall near the Exp 8 setup
for your energy calibration.
- For this experiment, and also exps VII and IX, here is a brief
description on using either the Tektronix
2245A or the digital Tektronix
TDS360 scopes.
Experiment IX: Gamma-Gamma
Angular Correlation
- See the notes in exp VII regarding data acquisition.
- Use the fast oscilloscope (Tektronix
2245A or Tektronix
TDS360) from exps VII/VIII or exp XI to check the coincidence
timing! Follow the signals all the way through the circuit to make sure
the signals going into the coincidence circuit are properly timed.
- There is a stronger 60Co source inside the little
lead can in the lead-lined box. The metal rod (not the block) is the
active area of the source. Calculate for yourself how much stronger
this source is than the one in the wooden box.
- The detection efficiency of the two-detector system changes as a
function of angle. This affects the overall shape of the data. The
effect can be estimated using Monte Carlo techniques. Run the Monte
Carlo Program called MC.EXE(written by
Prof. CC Chang) to see the effect. It is located in the DOS
directory of programs on the lab computers.
- You will need to fit your data to either Legendre Polynomials, or
to equation IX-1 in the lab manual. A sample fitting program, using
EXCEL, can be found at p:\p405\Analysis
Tools\Excel Tools\ParaFit-mc.xls. This is a parabolic fit with 3
parameters. The data have been entered such that the independent
variable is cos^2(theta). It's rather clumsy, but functional.
Experiment X: The Hall
Effect in Metals
- You MUST go over the vacuum system with either Allen Monroe, Tom
Baldwin, or one of the instructors before starting the experiment! See
also Appendix A.
- You will need to take a look at Appendix
E on sample preparation, which is not in the lab manual.
- See one of the instructors regarding thickness measurements:
there is a relatively new apparatus donated by Dr. Webb. A manual
for it can be found in this Appendix
D.
Experiment XI: Cosmic Rays
- To get the solid angle of the detector system, you have to do a
four-dimensional integral: you can either use Mathematica, or you can
look for the nifty little pascal program written by Prof. C.C. Chang,
called INTEGRAL.EXE, which is located on
the P405 PCs in p:\p405\exp11\ .
- Figure XI-2 in the lab manual is OK, but not quite accurate. This
one is a little better.
- Use the digital oscilloscope (Tektronix
TDS360) to check the coincidence timing.
- BE SURE THE HV SUPPLY is set to NEGATIVE (-)!
- Further information on the various components of cosmic rays can
be found in the Particle Data Group's Review of Particle
Properties. Look under Astrophysics and Cosmology, then under
Cosmic Rays.