Authors:Justin McIntyre, Mathew Cooper, April Carman, Theodore Bowyer, Anthony Day, Derek Haas, James Hayes, Tom Heimbigner, Charlie Hubbard, Kevin Litke, Michael Ripplinger, Brian Schrom, and Reynold Suarez
Absolute efficiency calibration of radiometric detectors is frequently difficult and requires careful detector modeling and
accurate knowledge of the radioactive source used. In the past we have calibrated the β–γ coincidence detector of the Automated
Radioxenon Sampler/Analyzer (ARSA) using a variety of sources and techniques which have proven to be less than desirable (Reeder
et al., J Radioanal Nucl Chem, 235, 1989). A superior technique has been developed that uses the conversion-electron (CE)
and X-ray coincidence of 131mXe to provide a more accurate absolute gamma efficiency of the detector. The 131mXe is injected directly into the beta cell of the coincident counting system and no knowledge of absolute source strength
is required. In addition, 133Xe is used to provide a second independent means to obtain the absolute efficiency calibration. These two data points provide
the necessary information for calculating the detector efficiency and can be used in conjunction with other noble gas isotopes
to completely characterize and calibrate the ARSA nuclear detector. In this paper we discuss the techniques and results that
we have obtained.
The Analytical Development Section of Savannah River Technology Center (SRTC) was requested by the Facilities Disposition Projects (FDP) to determine the holdup of enriched uranium in the 321-M facility as part of an overall deactivation project of the facility. The 321-M facility was used to fabricate enriched uranium fuel assemblies, lithium-aluminum target tubes, neptunium assemblies, and miscellaneous components for the production reactors. The results of the holdup assays are essential for determining compliance with the Waste Acceptance Criteria, Material Control & Accountability, and to meet criticality safety controls. This report covers calibration of the detectors in order to support holdup measurements in the C and D out-gassing ovens. These ovens were used to remove gas entrained in billet assembly material prior to the billets being extruded into rods by the extrusion press. A portable high purity germanium detection system was used to determine highly enriched uranium (HEU) holdup and to determine holdup of 235U, 237Np, and 241Am that were observed in these components. The detector system was run by an EG&G Dart system that contains the high voltage power supply and signal processing electronics. A personal computer with Gamma-Vision software was used to control the Dart MCA and provide space to store and manipulate multiple 4096-channel -ray spectra. The measured 237Np and 241Am contents were especially important in these components because their presence is unusual and unexpected in 321-M. It was important to obtain a measured value of these two components to disposition the out-gassing ovens and to determine whether a separate waste stream was necessary for release of these contaminated components to the E-Area Solid Waste Vault. This report presents determination of the calibration constants from first principles for determination of 241Am and 237Np using this detection system and compares the values obtained for 237Np with the calibration factors obtained with a subsequent measurement using a point source of radioactive equilibrium 237Np/233Pa.
Authors:K. Abel, A. Schilk, D. Brown, M. Knopf, R. Thompson, and R. Perkins
A large area beta scintillation detector has been developed which is currently capable of determining Sr-90/Y-90 contamination in surficial soils. The detector system employs scintillating fiber optic arrays, with active dimensions approximately 15 cm wide by 100 cm long, both ends of which are coupled to multiple photomultiplier tubes (PMTs). Electronic processing includes coincidence requirements to optimize sensitivity and selectivity for the 2.28 MeV (maximum) beta particle from Y-90. Low energy beta particles and gamma rays are discriminated against using double ended and multi-layer coincidence requirements. The detector system is personal-computer-software controlled and data restored in a format compatible with standard database software for ease of final data reduction. Experimental calibration studies have shown a linear response for Sr-90/Y-90 soil concentrations from 12 to over 500 pCi/g and a discrimination factor of 50 to 1 versus Cs-137.
The self-attenuation correction factor is used to relate the efficiency for a sample with a given matrix to the efficiency for an ideal sample with identical geometry but negligible photon attenuation. A certain linear relation for the efficiency for a given sample as a function of the efficiencies for a number of subsamples into which the original sample can be decomposed is established and experimentally validated. This relation can be used also in the case when the sample and the subsamples have different matrices. In this way the efficiency for volume samples with arbitrary compositions and densities can be constructed on the basis of the efficiencies (independently measured) for a number of basic geometries. Also a possibility to check the consistency of efficiency calibrations carried out with different standard sources (with different matrices) is provided.
Two compounds are described with interesting properties for use in DSC. The first compound is adamantane (C10H16), with a reversible solid-solid transition at 208.62 K , suitable for DSC calibration at this low temperature . The second compound is 4,4'-azoxyanisole (C14H14N2O3), with a liquid crystal range between 390 and 407 K . This compound shows two transitions on heating, with a large heat effect at 390 K and a small heat effect at 407 K. For this reason, this substance is well suitable for testing the sensitivity and the resolution of DSC instruments . For both compounds not only the heating, but also the cooling behaviour is investigated.
The LabSOCS software performs mathematical efficiency calibration of Ge detectors. Extensive tests have been conducted comparing the LabSOCS efficiency calibration with those from traditional radioactive sources for typical laboratory geometries. For this study, 4 NIST-traceable standards containing 13 different energy lines were counted in 7 different geometries that are typical of laboratory samples. The results from the first 13 detectors produced using this process show that efficiency calibrations generated with LabSOCS have an accuracy of 5.1% SD at low energies and 4.2% SD at high energies.
Authors:L. Bennett, D. Sims, W. Andrews, and K. Nielsen
A computer program entitled SCAAP (Set-up, Calibration, Acquisition and Analysis Program) has been designed to make gamma-ray spectroscopy easily useable by staff in laboratories at the Slowpoke-2 Facility at RMC and in support of the Canadian Forces Nuclear Emergency Response Teams (NERTs). The former group utilises gamma-ray spectroscopy for neutron activation analysis (NAA), while the latter may need to have inhalation dose rates calculated. The intent of this program, written using Microsoft Visual Basic, is to provide a simplified interface between the operator and the spectroscopy equipment and to provide the calculations necessary to produce results quickly. There are five sections (Setup, Calibrate, Acquire, Analyse and NAA) of which the first four are linked. In these sections, a checklist of procedures is presented and automated for the user to set up and calibrate the equipment and then to analyse spectra to provide various dose rates. In the unlinked section, NAA, gamma-ray spectra are analysed to provide elemental concentrations in samples.
Authors:R. McDonald, A. Smith, D. Hurley, E. Norman, and M. Schoonover
Following many years of productive research, the 184-inch Cyclotron, the SuperHILAC, and the BEVALAC accelerators at the Berkeley
Laboratory were closed, leaving thousands of concrete shielding blocks available for reuse, recycling, or disposal. The process
history of these blocks precludes free release pending radiological characterization. This paper describes a procedure whereby
a high efficiency shielded germanium spectrometer is used to rapidly characterize natural and man-made activity within the
blocks. The spectrometer is moved up to the block and 5 minutes of data are collected at the point on the block that registers
highest on a micro-R meter. Sensitivity is better than 1 pCi/g (0.037 Bq/g) for Co-60 and Eu-152, the prominent man-made activities
observed. One-time calibration of the detector system is obtained from a sample of concrete, drilled with a hammer drill,
counted in our low-background facility, and compared to crushed rock with known U, Th, and K activity. A simple relationship
exists between the counts/minute observed in a characteristic gamma-ray peak and the activity in the block.
In order to calibrate a gamma-ray spectrometer for radioactivity measurements in environmental samples, it is essential to
use standard radioactive sources in the appropriate geometrical configuration. However, the lack of standard sample due to
any reason would necessitate the use of reference materials as reliable alternative. They often appear in many matrices and
densities. Accordingly, special attention should be drawn towards optimizing the calibration. This work studies the errors
encountered because of the attenuation process due to the density difference of the samples (including reference samples)
aliquots with identical matrix contents. The highest effect was noticed in the lower energy regions. This study suggests that
even for the reference samples with the same matrix, it is necessary to set a recommended density for the measurement process
to avoid the errors due to the attenuation. If this is not practically possible it is recommended that attenuation correction
due to matrix contents followed by another correction due to density correction would be a reliable approach to reach an optimum