1. The Detection of Radioisotopes Using a Thin Scintillating Fiber in a Spiral Adam Jernigan and Eric Blue Advisor: Dr. Thomas Dooling The University of North Carolina Pembroke Monte Carlo Method The purpose of this experiment was to develop an inexpensive detector, for radioactive isotopes, that could be used in fieldwork. This experiment required the use of a thin, long, inexpensive, plastic scintillator fiber, cardboard tube, aluminum foil, multi-channel analyzer, voltage source, and a computer. The sources used for the experiment were Sr-90, Tl-204, Cs-137 and Co-60 allowing for studies of both gamma and beta radiation. These source types are the most prevalent in the biomedical and chemical fields. Through this process a simulation of the apparatus was designed in a Monte Carlo program using C++. Initially the scintillator cable was placed into a dark box through which readings were taken, to determine the attenuation of light in different positions on the cable. This attenuation curve was used, in the Monte Carlo program, to simulate the experiments and account for the attenuation of light as it propagates through the cable when it is spiraled around the cardboard tube. The cable was then tested in a spiral configuration wrapped around a tube. Small radioisotope samples were passed through the center of the tube, allowing detection of the source by the cable. Experimental and Monte Carlo results are compared and the sensitivity of the detector, to source type and location, are reported. Purpose In trying to develop this spiral code the goal was to try to develop an efficient method for detecting radioactive sources. The theory was that with a plastic scintillator cable wrapped around a tube would allow the source to be passed through it and still give a reasonable energy distrubution without much distortion. Geometry The spiral scintillator code was programmed as if a thin piece of fiber optic cable were wrapped around a cardboard tube. Then, a radioactive source would be lowered through the center of the tube and the simulated data collected. Basic Scintillator Diagram The adjacent diagram shows the system that was used to experimentally produce measurements of a long, thin, spiral scintillator cable. This system was used to set base runs for our other mentioned setups and to produce attenuation curves that were later needed. Spiral Diagram The diagram to the right shows the setup used to test our sources and spiral code. We have a cardboard tube wrapped with aluminum foil and then a Plastic Scintillator Cable with an average distance of 3 cm between coils. The cable is then wrapped by another layer of aluminum foil to help trap escaping rays. The last bit of cable was used to connect to the phototube, which was connected to a Multi Channel Analyzer and a Voltmeter. Monte Carlo Flowchart The figure to the right shows the sequence of events that forms the Monte Carlo program. The diagram tracks a particle through the simulated plastic scintillator based on the program and its subroutines. Tl-204 Tube Scintillator Runs Tl-204 Pulse Height and Scalar Compilation Graphs Sr/Y-90 Tube Scintillator Runs Sr/Y-90 Pulse Height and Scalar Compilation Graphs Co-60 Tube Scintillator Runs Co-60 Pulse Height and Scalar Compilation Graphs Cs-137 Tube Scintillator Runs Cs-137 Pulse Height and Scalar Compilation Graphs Sr/Y-90 Tube Scintillator Monte Carlo Simulation Tl-204 Tube Scintillator Monte Carlo Simulation Co-60 Tube Scintillator Monte Carlo Simulation Cs-137 Tube Scintillator Monte Carlo Runs Materials Used Multi Channel Analyzer Company: Spectrum Techniques Multiple Settings Upper Level Discriminate: up to 105 Lower Level Discriminate: as low as 0 Coarse Gain: 2,4,8,16,32,64 Fine Gain: 1.00 – 2.00 Total Gain = Fine Gain * Coarse Gain Conversion Gain: 256,512,1024,2048 Live Time: The time data is available to take Real Time: Actual time the MCA takes data (Real time may be higher than live time) PRICE : $1000 Hamamatsu Phototube Company: Hamamatsu Series: H5783/H6780 Dimensions: Length: 22.0 mm Width: 22.0 mm Height: 50.0 mm This phototube has an optimum Wavelength spectrum from 420 nm to 630 nm which falls in the visible light spectrum corresponding respectively to violet and orange light. PRICE : $ Radiation Sources Company: Spectrum Techniques Cobalt 60 :Gamma Ray producer Activity per second: 1.0 µ Ci. Cesium 137: Beta Particle & Gamma Ray producer Activity per second: 5.0 µ Ci Strontium 90: Beta Particle producer Activity per second: 0.1 µ Ci Thallium 204: Beta Particle producer Activity per second: 1.0 µ Ci. PRICE : $250 Scintillator Paddle Company : Bicron (Saint-Gobain Crystals) Blue-Emitting Plastic Scintillator Sheet 305 x 305 x 5mm PRICE: $150.00 Final Acknowledgements Acknowledgement: This work was supported by the National Science Foundation’s Research Experience for Undergraduates program.(CHE-0353724) References: Hamamatsu Phototube http://usa.hamamatsu.com/index.php?id=13195780&langu age=1& Radioactive Sources http://www.spectrumtechniques.com/radioisotopes.htm UCS 20 Spectrometer Multi Channel Analyzer http://www.spectrumtechniques.com/ucs20.htm Physics Constants http://www.physics.nist.gov/ Stopping Power Curves http://www.physics.nist.gov/PhysRefData/Star/Text/ESTAR.html National Science Foundation Research Experiences for Undergraduates http://www.nsf.gov/funding/pgm_summ.jsp?pims_id=5517 &from=fund Isotopes Through this phase of the testing there were five main isotopes used. Sr-90 (beta source), Activity Level (0.1 uCi), Half Life (28.6 yrs.) Tl-204 (beta source), Activity Level (1.0 uCi), Half Life (3.78 yrs.) Y-90 (beta source) Cs-137 (gamma source), Activity Level (5.0 uCi), Half Life (30.2 yrs.) Co-60 (gamma source), Activity Level (1.0 uCi), Half Life (5.27 yrs.) There were other sources used which consisted of: I-131 (beta source) Sr-89 (beta source) Ir-192 (beta source) All Experimental Scintillator Runs were 30 min runs.