Lab 02: Excitation Levels of Neon

Summary

In this lab we measured one of the ionization potentials for neon. We did this by running a current through a tube filled with neon. The electrons are freed into the neon and then recollected at a ring set at a steady voltage in the middle of tube. The collector ring voltages we used for this were 1.8 and 2.1. Then the voltage at which electrons enter the tube is varied at regular intervals. The kinetic energy that the electrons lost in collisions with neon atoms that ionized the atoms is then read by the picoamplifier as current. When the current jumps the neon atoms are being ionized. We did a rough and a fine scan for each collector ring voltage we chose. Before this, we did a rough scan with the potential reversed.

For the first rough scan, we set the voltage to the collector ring to 2.1 and we increased the input voltage 1 volt at a time, measuring the current at each increment, from 1 to 25 volts. Then we switched the potential of the collector ring by switching the wires connected to the negative and positive ends of the battery and repeated the rough scan as described. Then we did a fine scan with the collector ring voltage set to 2.1, going from 15 to 22 volts in increments of 0.1 volts. Then we set the voltage to the collector ring to 1.8 and we increased the input voltage 1 volt at a time, measuring the current at each increment, from 1 to 25 volts in a third rough scan. Then we did a fine scan with the collector ring voltage set to 1.8, going from 15 to 22 volts in increments of 0.1 volts. We graphed the results of our data to see the peak that represented the ionization energy being reached.

• In this lab I worked with Brian P. Josey.

• These are my Detailed Lab Notes.
  
  

This is our set up. From left to right: Picoamplifier connected on top of the Alarmed Meter, behind that is the Hertz Critical Potentials tube filled with neon and tube stand, next to them are the two Power Pupplies, on top of the Power Supply farthest right is the Digital Multimeter, in front of the power supplies if the DC battery set up with the red and black cables.

Analysis

These graphs were made with MATLAB 7.8. The peaks in the graphs indicate where the first ionization potential for neon is in electron volts per atom.

The accepted value from Dr. Gold's Lab Manual for the desired ionization energy of neon is 21.56 electron volts per atom.

The average of the values from our 4 scans was 19.52 +/- 0.01 electron volts per atom.

[math]\displaystyle{ (18.99 + 19.4 + 19.71 +19.99)/4 = 19.5225 }[/math]^{SJK 03:35, 21 December 2010 (EST)}

03:35, 21 December 2010 (EST)
Since the filament voltage is obviously affecting the locations of the peaks, is it appropriate to average values from differing voltages?

This indicates that there is a relative error of 9.45%.

[math]\displaystyle{ (21.56-19.5225)/(21.56) = 9.45 }[/math]%

There is a shift from the known value so there were likely systematic errors in our set up as suggested in Dr. Gold's Lab Manual. There were also errors caused by vibrations to the delicate set up.

Conclusion

In this lab I learned about one way the ionization potential for gases are obtained. I learned how to use a picoamplifier and how to read the set up diagram for the wiring. Joseph Frye and Alex Benedict helped us get set up and answered our questions patiently. If I did this lab again, I would find a way to protect the set up from vibration. To improve this lab in the future, numbered instructions with the set up diagram should be included. If there were a way to increase the resolution of the data so that increments of 0.05 volts could be obtained without major fluctuations in readings, the other two bumps in the graph could measured better.