Difference between revisions of "MainPage:Nuclear:Summer2015:ChristianPbWO4"
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One concern with the equation is that it is very sensitive to fractions of a millimeter. This makes diligence in measurements very important. Unfortunately, I did not discover the my best method until near the end of my work. Therefore, for most of the refractive index measurements, the uncertainty is fairly high, around ±.25. I was able to reduce this number to closer to ±.15 for my final measurements. | One concern with the equation is that it is very sensitive to fractions of a millimeter. This makes diligence in measurements very important. Unfortunately, I did not discover the my best method until near the end of my work. Therefore, for most of the refractive index measurements, the uncertainty is fairly high, around ±.25. I was able to reduce this number to closer to ±.15 for my final measurements. | ||
| − | ==== | + | ==== Results & Conclusions ==== |
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| + | With my measurements, I calculated the refractive index of 5 crystals. There was about a XY% varience between them. Due to the high error, however, we cannot make any conclusions about any one crystal being inherently different. The calculated refractive indices of the crystals agree with literature, which gives confidence to the quality of the crystals. | ||
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| + | [[File:RI.jpg]] | ||
== Transmittance == | == Transmittance == | ||
Revision as of 09:54, 7 August 2015
Overview
At the Jefferson Lab (JLab) in Newport News, VA there is an electron accelerator which launches electrons into different halls. Each hall has its own specific targets for the electrons and detecting equipment for results of the collision. In Hall C a high momentum spectrometer and a variety of detectors are used. However, there is no detector for neutral particles. The JLab is creating the neutral particle spectrometer (NPS). One of the major components of the NPS will be PbWO4, a crystal which scintillates, releasing photo-electrons, when hit by particles. These photo-electrons can then be picked up by a Photo Multiplier Tube (PMT) which uses high voltage to allow for the detection of individual photons. It is imperative that the characteristics between the crystals remains uniform.
Goals
1. Collect data on the light yield, transmittance, and refractive index of multiple crystals.
2. Check the data to confirm that the crystals meet the parameters needed for the NPS.
3. Compare the data between different crystals to analyze their uniformity.
Refractive Index
The refractive index of a material is defined as the ratio of speed of light in a vacuum to the speed of light in the material. As the light changes speed within a material it also bends. Snell's law relates the angle of incidence, refractive indices, and angle of refractive between two materials.
An equation
Using Snell's law:
n1\sinΘ1 = n2\sinΘ2
and some geometry, I, with the help of Marco, was able to create an equation which solved for the refractive index (n) as a function of the width of the crystal(L), the displacement of the laser(Δx), and the angle of incidence (Θ). Since the crystal reflects light well, the angle of incidence can be calculated by measuring the angle of reflectance and dividing that by two.
Measurements
Uncertainty
One concern with the equation is that it is very sensitive to fractions of a millimeter. This makes diligence in measurements very important. Unfortunately, I did not discover the my best method until near the end of my work. Therefore, for most of the refractive index measurements, the uncertainty is fairly high, around ±.25. I was able to reduce this number to closer to ±.15 for my final measurements.
Results & Conclusions
With my measurements, I calculated the refractive index of 5 crystals. There was about a XY% varience between them. Due to the high error, however, we cannot make any conclusions about any one crystal being inherently different. The calculated refractive indices of the crystals agree with literature, which gives confidence to the quality of the crystals.
Transmittance
The transmittance of a material is the the fraction of incident electromagnetic power that is transmitted through a sample. Knowing the transmittance of the crystals tells us: a) if the crystal is of the right characteristics for the detector. The detector requires a crystal which transmits at least 60% of light at a wavelength of 420nm. b) if there is uniform characteristics between the crystals. Further, using Fresnel's equations, it can be used to double check the refractive index.