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The 42nd Annual Midyear Meeting
of the Health Physics Society |
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The 42nd Annual Midyear Meeting
of the Health Physics Society |
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P. Tomorrow's Gamma-Ray Spectroscopy Technology: Transition Edge Sensors with 47 eV Energy Resolution at 103 keV. ; Johnson T*, Colorado State University; Ullom J, NIST, Boulder, CO; Rabin M, LANL, Los Alamos, NM
Abstract: Transition edge sensors (TES) are a novel high-energy-resolution gamma-ray spectrometer for nuclear materials analysis. Our prototype has demonstrated energy resolutions of 47 eV at 103 keV as compared to resolutions of ~500 eV using present state-of-the-art Germanium spectrometers. The prototype consists of a 14-pixel multiplexed array of transition edge sensor microcalorimeters operated inside a cryogenic dewer. The TES microcalorimeter consists of a thin-film bilayer of molybdenum (Mo) and copper (Cu) as a superconducting thermometer with a tin (Sn) photon absorber. The TES microcalorimeter functions on the principle that at low temperatures (~0.1 K), the sensor has an extremely small heat capacity. Therefore, heat deposited in the absorber by interacting gamma-ray photons increases the TES’s temperature and thus, increases the resistance of the superconducting Mo/Cu bilayer thermometer. The energy of the photon is measured as a pulse-shaped decrease in the calorimeter’s current. Single-pixel TES microcalorimeters of ~1 mm2 provide slow count rates of 50-100 counts/second. The Quantum Devices Group, National Institute of Standards and Technology, working with Los Alamos National Laboratory, successfully demonstrated a 14-pixel array of TESs to increase the system count rate and collection area. Group research focuses on increasing the array size to 256 pixels, which will then provide system count rates and collecting areas comparable to Germanium spectrometers but achieve sub-100 eV energy resolutions. Mature evolutions of the TES array technology are ideal for non-destructive assay of nuclear materials because the unmatched energy resolution enables separation of spectral peaks in the complicated plutonium (Pu) gamma-ray spectrum. | ||
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P. Detect On-line, Ultra Low Radiation Using statistical methods. Grof Y*, CEMRC Carlsbad; Akbarzadeh M, WTS Carlsbad; Monk J, CEMRC Carlsbad grof@cemrc.org
Abstract: There is a need for early detection of contamination in sites that are processing, shipping or disposed radioactive materials. We develop a system which can detect very low concentration of radioactive isotopes, especially TRU (Trans- Uranium) isotopes. The system is measuring on line and it can be connected to the air monitoring at the site. Results showed very short response and very low concentration compare to other systems. The system is based on a statistical forecasting method which is learning the environment behave and compare the actual results to the forecasting. The method eliminates all the natural and regular radiation exposure in the environment. Remaining only the clear view of the contamination. The first results from the system, using a very simple GM detector, show that the system can detect levels of Pu-239 contamination smaller then 20 dpm with very simple analyzing tool. We intend to use a more sophisticate detector and a better analyzing tool and the detection limit will be lower then 1 dpm. | ||
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P. C++ Computer Code for Exact Decision Levels And Errors of Type I When The Sample Count Time Is An Integer Times Greater Than The Background Count Time. Potter WE*, Consultant, Sacramento, CA; Strzelczyk J, University of Colorado Hospital, Aurora, CO pspr189729@aol.com
Abstract: In the past there have been papers where the blank (background) is counted for the same amount of time or longer than the sample. In emergency and cleanup operations situations may arise where the sample is counted longer than the blank. In particular, it is well known that the optimum ratio of blank count time to sample count time equals the square root of the ratio of the respective count rates. The presented approach assumes that both the blank count and the sample contribution to the gross count are Poisson distributed. Also it is assumed that the expected blank count is known. The net count is transformed into an integer. A code in C++ computes the exact probability density function for the transformed net count when there is no activity in the sample. The validity of the computations is verified by checking that the sum of probabilities is close to 1.0 and that the expected value of the net count is close to zero. The decision level is determined by summation of the right tail of the probability density function when there is no activity in the sample. Activity is said to have been detected if the observed net count is greater than the decision level. The code runs on the current Microsoft operating systems. The entire C++ code for decision levels is given. This code could be expanded to yield codes for detection limits and confidence intervals. The computed results are compared with the usual Poisson-normal approximation for the decision level. Minimally the computed results are valid for expected blank counts in the sample count time <= 300.0, ratios of the sample count time to the blank count time <= 20, and errors of type I >= 0.001. Uncertainty in the expected blank count can be readily examined by utilizing confidence intervals for the expected value of a Poisson distribution in conjunction with the code. | ||
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P. Optically Stimulated Luminescence (OSL) Of Tooth Enamel And Its Potential Use For Triage In Radiation Emergencies. DeWitt R*, Oklahoma State University; Klein DM, Oklahoma State University; Yukihara EG, Oklahoma State University; Simon SL, National Cancer Institute; McKeever SWS, Oklahoma State University rkalchg@okstate.edu
Abstract: Optically stimulated luminescence (OSL) properties of dental enamel are discussed with the goal of developing an in-vivo dose assessment technique for medical triage following radiation emergencies. In the OSL technique, past radiation exposure is assessed by stimulating the sample with light of one wavelength and monitoring the luminescence at another wavelength. It is assumed that the luminescence originates from radiation-induced defects in the enamel and that the intensity of the luminescence signal is in proportion to the absorbed radiation dose. Several primary findings emerged from this research: (a) sensitivities varied considerably between different teeth and also between fragments of the same tooth, (b) OSL signals were found to decay rapidly during the first 12 hours after irradiation and slower afterwards, (c) the fading rate of the luminescence signal varied between fragments, (d) blue light stimulation yields greater sensitivity than infra-red stimulation, while the OSL signal obtained with a high-intensity pulsed green-light laser was found to be not correlated with the radiation dose. The rapid fading of the OSL signal, while a disadvantage for assessing doses at long-times after exposure, provides the distinct advantage that OSL measurements after an exposure event would not be significantly confounded by prior medical or occupational exposure. Significant challenges remain to developing a practical in-vivo technique including the development of calibration procedures and lowering minimum detectable doses. | ||
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P. RSAC 7 - Radiological Dose Consequence Software. Schrader BJS*, Idaho National Laboratory bradley.schrader@inl.gov
Abstract: RSAC 7 is the next generation in software for dose consequence assessment. Easy to use yet diversified in its application. RSAC 7 can calculate the acute dose from an RDD to accident events. RSAC has been in continuous use since 1964. RSAC 7 is a Windows® compatible software program that calculates complete radioactive daughter in-growth and decay during all event phases. The calculation of fission product inventories is particularly useful in the analysis of scenarios where the short-lived radionuclides change rapidly as a function of decay time or accidents with criticality excursions. RSAC 7 has provisions for calculating release from an operating reactor. Provision is also made for users to import fission product, actinide and activation product inventories calculated using other codes when desired. Radionuclide inventories can be fractionated and decayed to simulate transport through a process or clean-up system such as HEPA filters. Inventory fractionations may be done by chemical group, by element or by fraction of the entire radionuclide inventory. Complex release scenarios to the atmosphere can be modeled with RSAC 7. Resuspension of radioactive particulate from such factors as vehicle traffic to fires can be calculated. Airborne and ground surface concentrations are calculated such that radiological dose to a person or population can be estimated. Total dose is calculated for the inhalation and ingestion internal pathway and the external ground surface and cloud gamma pathway. RSAC 7 includes dose conversion factors from both FGR 11/12 and ICRP 68/72. | ||