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Beta contamination monitor energy response

Description: Beta contamination is monitored at Los Alamos National Laboratory (LANL) with portable handheld probes and their associated counters, smear counters, air-breathing continuous air monitors (CAM), personnel contamination monitors (PCM), and hand and foot monitors (HFM). The response of these monitors was measured using a set of anodized-aluminum beta sources for the five isotopes: Carbon-14, Technetium-99, Cesium-137, Chlorine-36 and Strontium/Yttrium-90. The surface emission rates of the sources are traceable to the National Institute of Standards and Technology (NIST) with a precision of one relative standard deviation equal to 1.7%. All measurements were made in reproducible geometry, mostly using aluminum source holders. All counts, significantly above background, were collected to a precision of 1% or better. The study of the hand-held probes included measurements of six air gaps from 0.76 to 26.2 mm. The energy response of the detectors is well-parameterized as a function of the average beta energy of the isotopes (C14=50 keV, Tc99=85, Cs137=188, C136=246, and Sr/Y90=934). The authors conclude that Chlorine-36 is a suitable beta emitter for routine calibration. They recommend that a pancake Geiger-Mueller (GM) or gas-proportional counter be used for primarily beta contamination surveys with an air gap not to exceed 6 mm. Energy response varies about 30% from Tc99 to Sr/Y90 for the pancake GM detector. Dual alpha/beta probes have poor to negligible efficiency for low-energy betas. The rugged anodized sources represent partially imbedded contamination found in the field and they are provided with precise, NIST-traceable, emission rates for reliable calibration.
Date: December 31, 1998
Creator: Bjork, C.W. & Olsher, R.H.
Partner: UNT Libraries Government Documents Department

Radiological contamination penetration depth in Fernald transite panels

Description: To characterize the penetration depth of radiological contamination through the thickness of transite (an asbestos-cement building material) from the Department of Energy (DOE) Fernald site, both destructive and non-destructive analysis techniques were used. The destructive techniques were based on progressively removing layers of material and subsequent direct analysis of successive surfaces. These laminar analyses included quantitative measurements using a Geiger-Mueller (G-M) detector and qualitative measurements based on autoradiography and ultraviolet photography. G-M detector measurements during layer removal provided quantitative distributions consistent with diffusion theory and have served to validate a novel non-destructive technique. The ultraviolet analysis provided qualitative information with the advantage of instantaneous results that may be useful for screening samples. The autoradiographic analysis also provided qualitative results for comparison and image analysis. Both quantitative and qualitative results from this study indicated that the contamination did penetrate into the volume of the transite. However, this penetration depth was observed to be strongly dependent on the manner in which the transite was exposed to the contamination. Consequently, it is likely that significantly different penetration depths will be observed for different processes, buildings, and sites.
Date: December 6, 1995
Creator: Russ, W. R.; Valentine, J. D. & Chung, Wei
Partner: UNT Libraries Government Documents Department

MESERAN Calibration for Low Level Organic Residues

Description: Precision cleaning studies done at Honeywell Federal Manufacturing & Technologies (FM&T), the Kansas City Plant (KCP), and at other locations within the Department of Energy (DOE) Weapons complex over the last 30 years have depended upon results from MESERAN Evaporative Rate Analysis for detecting low levels of organic contamination. The characterization of the surface being analyzed is carried out by depositing a Carbon-14 tagged radiochemical onto the test surface and monitoring the rate at which the radiochemical disappears from the surface with a Geiger-Mueller counter. In the past, the total number of counts over a 2-minute span have been used to judge whether a surface is contaminated or not and semi-quantitatively to what extent. This technique is very sensitive but has not enjoyed the broad acceptance of a purely quantitative analysis. The work on this project developed calibrations of various organic contaminants typically encountered in KCP operations. In addition, a new analysis method was developed to enhance the ability of MESERAN Analyzers to detect organic contamination and yield quantitative data in the microgram and nanogram levels.
Date: April 8, 2004
Creator: Benkovich, M.G.
Partner: UNT Libraries Government Documents Department

Absolute Thermal Neutron Determination. Part 2. Absolute Beta Counting of Indium Foils

Description: Correction factors for the effect of thickness on the selfscattering, self-absorption, and backscattering of beta particles from indium foils were determined for irradiated foils of 0.03 to 100 mg/cm/sup 2/. The data were corrected for the activity produced by epithermal neutrons, self-shielding of thermal neutrons by the foil during irradiation, the backscatter from the foil support, and the contributions of gamma and x rays to the counting rate. The multiple beta spectra of indium produced a minimum in the self-absorption and self-scattering correction curve in the GM detector at approximately 1 mg/cm/ sup 2/ and a maximum at approximately 12 mg/cm/sup 2/. The selfabsorption curve for indium in the 2 pi counter has the expected shape for a beta emitter with multiple spectra. The self-scattering and self-absorption correction factors for a 100 mg/cm/sup 2/ indium foil are approximately 1.5 for a GM detector at 7% geometry and approximately 3 for a 2 pi counter. (D.L.C.)
Date: October 1, 1955
Creator: Koontz, R. L.; Greenfield, M. A. & Jarrett, A. A.
Partner: UNT Libraries Government Documents Department

MEASUREMENT OF ELECTRON ATTACHMENT IN OXYGEN-METHANE AND OXYGEN-CARBON DIOXIDE MIXTURES

Description: The formation of heavy negative ions by the attachment of low-energy electrons to oxygen molecules was studied for small amounts of oxygen mixed with methane or carbon dioxide. The rate of attachment in both cases was found to depend on the electron energy, the pressure of the oxygen and the non-attaching gas, and on the kind of non-attaching gas. In general, the attachment increases as electron enprgy decreases or as either oxygen or total pressure increases. The value of the attachment coefficient in oxygencarbon dioxide mixtures is about 100 times its value in oxygen-methane mixtures. This large difference is probably due in part to differences in electron energy and partly to differences in the stabilizing qualities of the two molecules. Dissociative attachment, which should be pressure independent, does not occur at the low energies that were used in this work. Both methane and carbon dioxide are to differences in the stabilizing qualities of the two molecules. Dissociative attachment, which should be pressure independent, does not occur at the low energies that were used in this work. Both methane and carbon dioxide are sometimes used as filling gases for Geiger and proportional counters. The high sensitivity of carbon dioxide to oxygen contamination indicates that very pure gas should be used if the best operation is to be obtained. The low sensitivity of methane recommends it for counters where careful purification of the gas is difficult and particularly for flow counters where the possibility of contamination by atmospheric oxygen exists. (auth)
Date: January 25, 1960
Creator: O'Kelly, L. B.; Hurst, G. S. & Bortner, T. E.
Partner: UNT Libraries Government Documents Department

DETECTION OF ThO$sub 2$ CONTAMINATION IN SIMULATED CUTS AND ABRASIONS

Description: Tests have been made to determine the sensitivity of various radiation detection instruments for known amounts of ThO/sub 2/ contained in simulated cuts and abrasions. A shielded Geiger-Mueller counter tube can be expected to detect at least 0.1 mg ThO/sub 2/ when counting for a reasonable length of time provided the ThO/sub 2/ deposit is on the surface of the subject being counted. A shielded gamma-spectrometer-crystal, set at a 50-kev cutoff, can be expected to detect at least 0.5 mg ThO/sub 2/ even when an absorber equivalent to 1/2 in. of paraffin is placed between the crystal and the ThO/sub 2/ sample. Duration of exposure of standard film badge photographic emulsions is inversely proportional to the amount of material present and an exposure of about 300 hr is required to detect 10 mg of surface ThO/sub 2/. Although no information is available on the amount of thorium required to induce fibrosarcomas, an extrapolation of data for plutonium indicates that of the order of 1/2 gram of thorium must be present before occurrence of fibrosarcomas would be observed. This value does not represcnt a lower limit but is more likely to be a value for which occurrence of fibrosarcomas are a virtual certainty. It appears to be most desirable to experimentally determine the lower limit value for the amount of ThO/sub 2/ required to induce fibrosarcomas, noting that this may be as much as a factor of 100 smaller than the value cited above. (auth)
Date: January 15, 1959
Creator: Thomas, D.G. & Hilyer, J.V.
Partner: UNT Libraries Government Documents Department

A Statistical Model of Nuclear Level Spacings

Description: A generalization of Wigner's simple model for the distribution of nuclear level spacings is studied. The generalization is based on a stochastic process which reproduces the correct joint probabllity distribution of N energy levels for small spacings. The case N = 3, which includes the effect of the correlation between adjacent spacings, is discussed in detail. The resulting distribution and the correlation coefflcient are compared with experimental data. No definite conclusion can be drawn except that the effect of the correlations on the spacing distribution is very small. (auth)
Date: December 1, 1960
Creator: Dresner, L. & Inonu, E.
Partner: UNT Libraries Government Documents Department

Performance of the CEDS Accident Dosimetry System at the 1995 Los Alamos National Laboratory Nuclear Accident Dosimetry Intercomparison

Description: In July 1995, LANL hosted an accident dosimetry intercomparison. When all reactors on the Oak Ridge Reservation were idled in 1988, the Health Physics Research Reactor (HPRR), which had been used for 22 previous intercomparisons dating from 1965, was shut down for an indefinite period. The LANL group began characterization of two critical assemblies for dosimetry purposes. As a result, NAD-23 was conceived and 10 DOE facilities accepted invitations to participate in the intercomparison. This report is a summary of the performance of one of the participants, the Centralized External Dosimetry System (CEDS). The CEDS is a cooperative personnel dosimetry arrangement between three DOE sites in Oak Ridge, Tennessee. Many successes and failures are reported herein. Generally, the TL dosimeters performed poorly and always over-reported the delivered dose. The TLD processing procedures contain efforts that would lead to large biases in the reported absorbed dose, and omit several key steps in the TLD reading process. The supralinear behavior of lithium fluoride (LiF) has not been characterized for this particular dosimeter and application (i.e., in high-dose mixed neutron/gamma fields). The use of TLD materials may also be precluded given the limitations of the LiF material itself, the TLD reading system, and the upper dose level to which accident dosimetry systems are required to perform as set forth in DOE regulations. The indium foil results confirm the expected inability of that material to predict the magnitude of the wearer`s dose reliably, although it is quite suitable as a quick-sort material. Biological sample (hair) results were above the minimum detectable activity (MDA) for only one of the tests. Several questions as to the best methods for sample handling and processing remain.
Date: December 1, 1996
Creator: McMahan, K.L. & Schwanke, L.J.
Partner: UNT Libraries Government Documents Department