MainPage:Nuclear:Summer2015:ChristianPbWO4
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.
Measurements
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.