A Multi-Layer Phoswich Radioxenon Detection System (7th Qtr Report), Reporting Period 10/01/07 - 12/31/07

Description of activities conducted this report period: (1) Electronics Development--To improve the overall performance of the two-channel digital pulse processor (DPP2), the PCB has been redesigned and the new printed board is now under assembly. The system is enhanced with two new fast ADCs from Analog Devices (AD9230-250), each with a sampling rate of 250 MHz and a resolution of 12 bits. The data bus uses a high performance Low Voltage Differential Signaling (LVDS) standard. The offset and gain of each channel are separately controlled digitally by the GUI software. (2) GUI Software Development--A GUI is being developed using the Python programming language. All functions from the preceding MATLAB code have been re-implemented including basic waveform readout, pulse shape discrimination, and plotting of energy spectra. In addition, the GUI can be used to control sampling runs based on the number of pulses captured, either in real or live time. Calibration coefficients and pulse shape discrimination boundaries can be changed on the fly so that the detector may be characterized experimentally. Plots generated by the GUI can be exported as graphic data. At present, the software has only been tested using one channel, pending availability of the new DPP board (DPP2). However, the functions have been written to allow easy expansion to two channels. (3) Light Collection Modeling--The XEPHWICH design has been modeled to determine its light capture efficiency. Research in the 7th quarter includes additional simulations representing significant increase in data resolution, well over an order of magnitude greater than previous simulations. The final data set represents approximately 11 billion visible photons divided equally among 110 thousand data points. A laboratory experiment is being designed and executed to experimentally determine light capture efficiency as a function of position within the scintillators. (4) Radioxenon Fission Source--We have designed and constructed a fission chamber to be used for the collection of radioxenon gases following neutron bombardment of HEU in the Oregon State University TRIGA reactor. The aluminum housing and all vacuum fittings have been assembled, awaiting an HEU transfer from PNNL. Students have worked closely with PNNL and OSU Radiation Safety personnel to facilitate transfer of the HEU. The OSU TRIGA Reactor Operations Committee has approved the experiment. (5) Spectral (beta) Recognition--Spectral identification by a neural network developed in our laboratory was compared to that of solvers of a linear system of equations. Data indicate that our neural network is capable of identifying three beta emission sources ({sup 14}C, {sup 36}Cl, and {sup 99}Tc) simultaneously with reliability to within 3%