Physics307L F09:People/Rivera/Notebook/Excitation Levels of Neon
Excitation Levels of Neon
"The essence of this experiment is the demonstration of energy quantization of atoms, Ne in this case. This is achieved via inelastic e− scattering off Ne atoms. As such it is closely related to the original Franck-Hertz experiment (1914), which showed that an electron must have a certain minimum energy to make an inelastic collision with an atom. We now interpret that minimum energy as the energy of an excited state of the atom. It is strongly advised to read up on the Franck-Hertz experiment.
From a collision standpoint, free electrons colliding with orbiting electrons need to have at least the minimum energy required to excite the bound electrons to higher quantum levels. This experiment involves collecting these electrons after their atomic collisions, and determining the separate excitation energy levels that are available. The theory is quite simple. If an electron collides with a bound electron, and has suffcient energy to “move” the bound electron up into new orbits (or even ionize the atom), then the energy absorbed by the atom is lost to the free electron. This is an inelastic collision, and the free electron will slow down appreciably. In particular, it can now easily be captured by an anode positioned near the beam. As a function of the electron accelerating potential, VA, the number of electrons captured will increase rapidly near the energy levels of the atomic gas in the tube. These peaks in current will signal the energy levels of the atom."(from Physics 307 Lab Manual)
Apparatus and Setup
We used a Hertz Critical Potentials tube filled with neon connected to a Picoamplifier with Alarmed Meter, Power Supply and Digital Multimeter as shown in the figures to the right. We setup the apparatus to work with the multimeter and power supply so that we could read the exact voltage going into the apparatus. We then used the alarm to read the amps in the tube this should give the peaks where the excitation levels spike giving us the values for the different electron transitions possible in neon.
After two days of taking data and not getting any peaks I came back and used the alarm on the picometer to find the peaks. First I set the alarm tight around the signal so it would go off when a peak is passed while slowly sweeping the voltage being used. I was able to find two peaks with the alarm. I then took small measurements over that interval to find the profile of the peaks. I next took larger measurements around the peaks to show the overall curve coming into and out of the peaks. The peaks fell around 17.66eV and 18.45eV. These represent the 2p53s and 2p53p transitions. In our data there is also a peak around 20eV that represents the 14s,23d transition which is harder to see as while taking data this feature is less prevalent and therefore I didn't notice it until I was looking at the data while writing it up. If I had noticed it before I could have resolved it better while at the apparatus. The accepted peak values according to the Physics 307 Lab Manual appendix C for the first two peaks are 16.7eV and 18.65eV respectively. This gives us a 6% relative error in the 2p53s transition and a 1% relative error in the 2p53p transition.
In conclusion using the alarmed meter we were able to find two peaks similar to the ones in the manual. It was very important to keep the alarm close to the signal profile to see the peaks when they came by. I was glad to have the extra time on Wednesday to re-take data. I felt I learned a lot about the procedure and have a deeper understanding of the process involved. This experiment showed the quantization of atoms by showing that there are specific energies necessary to have an electron change states if this wasn't the case we wouldn't have spikes the curve would be constant as any energy would cause a state change. Here we see that there are quantized energies needed to make those transitions. I feel with more time to take readings we could have gotten lower percent error in our eV numbers and we could have easily with more time resolved the 14s,23d transition better and been able to find its peak with a lot more accuracy.