UCB Air Sampling Experimental Setup - System A
UCB Air Sampling Experimental Setup - System A
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The air sampling system resides on the top of Etcheverry Hall and consists of three sets of air pumps that suction air through a tube connected to a flow meter and a 0.2 micron filter. Most air particles will be deposited within the filter and this is the media we use to detect radioactivity.
After a period of time, the filters are removed from the pump apparatus and transported to our radiation counting laboratory. Our detector is a high-purity germanium (10%) detector that is surrounded by a 2" thick lead "cave" as shown below. The lead shields the detector from most normal background radiation that is emitted from materials such as concrete walls, floors, etc. within the laboratory. The filter is placed in a calibrated position near the detector and the cave is completely closed. Once the counting acquisition begins, if radioactive particles are present on the filter, the particles will decay and emit gamma radiation which may penetrate the detector surface and interact within the germanium semiconductor crystal. This will liberate electrons which produce a current proportional to the energy deposited by the gamma-ray photon. Our acquisition system then determines the energy by analyzing the signal pulse passed out of the detector to our computing system. After many interactions occur, the resulting spectra, shown below, will contain a number of discrete "lines" or "peaks" that are signatures used to discern the type of particles deposited within the filter.
The energy spectrum above is the result of counting for ~ 7 hours resulting in 30155 total counts spread from ~20keV to 3000keV. Peaks are present and are the result of natural background radiation within the laboratory entering the cave via a small port where detector cooling and electrical cables are inserted. This background tends to limit the sensitivity of the measurement as any detection of additional peaks must be statistically significant above this background level.
