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This study described the performance of an array of high-purity Germanium detectors, designed with two different end cap materials—steel and carbon fibre. The advantages and disadvantages of using this detector type in the estimation of the minimum detectable activity (MDA) for different energy peaks of isotope 152Eu were illustrated. A Monte Carlo model was developed to study the detection efficiency for the detector array. A voxelised Lawrence Livermore torso phantom, equipped with lung, chest plates and overlay plates, was used to mimic a typical lung counting protocol with the array of detectors. The lung of the phantom simulated the volumetric source organ. A significantly low MDA was estimated for energy peaks at 40 keV and at a chest wall thickness of 6.64 cm. [ABSTRACT FROM AUTHOR]

The Human Monitoring Laboratory has had a unique opportunity to measure two volunteers who had received 99mTc-labelled compounds for routine medical diagnosis to check the performance of its emergency monitoring equipment. The fixed and portable whole-body counters, some hand-held monitors and portal monitors were all used to measure the ‘radioactive’ persons. This study validated the current emergency calibrations that are being used, and has shown areas for improvement for equipment deployment that had not been previously anticipated. The results obtained suggest, for one individual at least, that the biokinetic model for 99mTc-methyl diphosphonate was not a good predictor of that person's metabolism. [ABSTRACT FROM PUBLISHER]

The National Internal Radiation Assessment Section (NIRAS), which operates the Canadian National Calibration Reference Centre for Bioassay and In Vivo Monitoring, has field deployable equipment for emergency response. A substantial part of this tool kit is a set of portal monitors that can be used to quickly screen people into the 'uncontaminated' and the 'contaminated'. The former term refers to a person who has <60 kBq (empirical practical detection limit) of activation/fission products and the latter group is contaminated by that amount or more. Recent field work has shown that one type of the NIRAS's portal monitors can be alarmed at significant distances if the level of contamination is high enough. The other types, which do not initiate a count until either an infra-red beam is broken or a proximity detector is activated, do not alarm but their background will be raised and this causes other problems. This paper proposes a method of group monitoring to help speed up the process of screening a large number of potentially contaminated persons using portal monitors. In short, the group of potentially contaminated persons will be kept isolated from the portal stations. Depending on a real-time estimate of the percentage of contaminated persons in the crowd, groups of persons will be selected for screening. The hypergeometric distribution has been used to decide on the sampling group size with an expectation that 90% of the time no contaminated person will be present in the group. Once removed from the main waiting area, the group will be pre-screened and then, depending on the result, sent to the appropriate portal. It is anticipated that this will greatly speed up processing as it substantially reduces the transit time. Transits times have also been estimated in addition to the number of personnel required to run all of NIRAS's field deployable equipment. [ABSTRACT FROM AUTHOR]

The sliced Bottle Manikin Absorber (BOMAB) phantom was originally proposed as an alternative to a commercially available phantom, but it suffers from the disadvantage of containing over 160 sources that need to be manufactured; however, it was found that the number of slices could be reduced substantially and that two slices in the sliced phantom gave the same performance characteristics over a wide energy range as a conventional BOMAB phantom for a particular counting system. This work explores the adaptability of this phantom to another counting geometry. The response of the Human Monitoring Laboratory's whole-body counter measuring this phantom with a decreasing number of planar sources has been modelled using MCNP5 over a wide energy range (122-2754 keV). It was found that the best agreement was obtained when the phantom contained 10 sources, I in the mid point of each section. As this is a different result from a previous finding, any other counting geometry will have to be assessed to determine the optimum loading if the sliced phantom is to be used. Also, it is clear that this type of phantom cannot be used for an intercomparison that will encounter different counting geometries, unless it contains a full loading of sources. [ABSTRACT FROM AUTHOR]

The Human Monitoring Laboratory has extended the use of sliced lungs containing planar sources to simulate heterogeneous radionuclide deposition patterns. This work examined two deposition patterns and their effect on the counting efficiency of low-energy photons. The results have shown that heterogenous distributions can be difficult to detect in some cases and can still lead to large uncertainties (up to a factor of 2.5) in the activity estimate, especially at low photon energies. At higher energies (~60 keV), the effect of the heterogeneous distribution is greatly reduced and errors in the activity estimate reduced ~25%. The presence of a heterogenous distribution can be detected by comparing the ratio of the individual detector counts with the expected values obtained from measuring multiple lungs sets that contained a homogeneous distribution. The distributions tested in this paper were detectable (at 2σ) as heterogeneous by two of the four detectors in the counting array. [ABSTRACT FROM AUTHOR]

The Human Monitoring Laboratory has field tested its Portable Personnel Portal (P3) Monitors using sources up to 1700 MBq (47 mCi) to determine the alarm distance as a function of activity. The results show that the P3 monitors are highly sensitive, so much so that siting will be a problem for multiple units if multiple alarms are to be avoided. Building materials will shield the monitors allowing units to be placed closer together than in the open where there is no shielding, but windows and doors reduce shielding and complicate the siting of multiple units. In either situation, careful prior thought should be given to siting the monitors and the logistics of the crowd control techniques. [ABSTRACT FROM AUTHOR]

Using the Lawrence Livermore National Laboratory (LLNL) torso phantom to calibrate a lung counting system can lead to the conclusion that three large area (i.e. >70 mm diameter) Ge detectors will outperform a four-detector array and provide a lower MIDA as a four-detector array of large area Ge detectors covers a significant portion of inactive tissue (i.e. non-lung tissue). The lungs of the LLNL phantom, which are ∼10 cm too short compared with real lungs, also suggests that a two-detector array could be used under limited circumstances. When tested with modified lungs that are more human-like, it was found that the four-detector array showed the best counting efficiency and the lowest MDA. Fortunately, these findings indicate that, although the LLNL phantom's lungs are too short, there is no adverse impact on the calibration of a lung counter. [ABSTRACT FROM AUTHOR]

The use of a lung phantom containing 152Eu241Am activity can provide a sufficient number of energy lines to generate an efficiency calibration for the in vivo measurements of radioactive materials ill tile lungs, However, due to the number of energy lines associated with 152Eu, coincidence ,summing, occurs and can present a problem when using such a phantom for calibrating lung-counting systems. A Summing Peak Effect Study was conducted at three laboratories to determine the effect of using an efficiency calibration based on a 152Eu241Am lung phantom. The measurement data at all three laboratories showed the presence of sum peaks. While one of the laboratories found only small biases (<) when using the 152Eu241Am calibration, tile other facilities noted up to 30% positive bias in the 140 keV to 190 keV energy range that prevents the use of the 152Eu241Am lung phantom for routine calibrations. Although manufactured by different vendors, the three facilities use similar types of germanium detectors (38 cm2 by 25 mm thick or 38 cm2 by 30 nun thick) for counting. These results underscore the need to evaluate tile coincidence summing effect, which appear system dependent, when using a nuclide such as 152Eu for the calibration of low-energy lung counting systems and highlight tile problem of using a general calibration curve in place of specific nuclide calibration factors. [ABSTRACT FROM AUTHOR]

A new stand has been designed to support the Bottle Manikin Absorber Phantoms when the phantoms are counted in the vertical position in a whole-body counter. The stand previously used by the Human Monitoring Laboratory was constructed from metal and was heavy to transport and making height adjustments to accommodate different phantom sizes was very time consuming. The new stand is constructed from lightweight plastic materials and allows easy height adjustments to accommodate different phantom sizes while supporting the weight of the phantoms. The stand was evaluated inside a whole-body counter at a nuclear-generating station and met all operational requirements for accessibility and ease of use. [ABSTRACT FROM PUBLISHER]

The performance characteristics of sliced lung sets were compared tolung sets with activity homogeneously distributed throughout the lung tissue substitute material. The activity estimate from planar sources differs from the estimate from homogeneous sources by a factor of 0.88 to 1.09 depending on the photon energy. This error is small compared to other uncertainties commonly encountered in lung counting, i.e., activity deposition in the lung, detector placement, size difference between individuals, etc. Sliced lung sets could be used instead of homogeneous lung sets to test or provide an interim calibration for a lung counting system. [ABSTRACT FROM AUTHOR]

The Human Monitoring Laboratory has compared the LLNL and JAERI torso phantoms using its germanium detector lung counting system by measuring the counting efficiencies for radioactive materials in the phantoms at photon energies of 17.7 keV, 59.5 keV, 121.8 keV, and 344 keV to assess the similarity (or differences) in performance characteristics. The counting efficiencies obtained from the two phantoms were compared by converting the Chest Wall Thickness data and Adipose Mass Fractions of the phantoms to Muscle Equivalent Chest Wall Thicknesses.The counting efficiencies for the two phantoms were found to be within a factor of 1.44 of each other at 17.7 keV, 1.30 at 59.5 keV, 1.25at 121.8 keV, and 1.17 at 344 keV when using a four detector array (JAERI efficiency divided by LLNL efficiency). However, individual detector responses show that the counting efficiencies from the two phantoms differ considerably in the region of the heart (up to a factor of 6 at 17 keV). Other areas above the lungs give counting efficiencies that are similar to each other. A routine intercomparison exercise with Cameco Corporation has shown that the counting efficiencies derived from the LLNL and JAERI phantoms were found to be within a factorof 1.18 (JAERI/LLNL) when a natural uranium lung set was used to calibrate a lung counter consisting of phoswich detectors. This work hasalso shown that over the energy range 63 keV-185 keV the LLNL phantom can be used to calibrate phoswich detector systems that are positioned on the back of the subject. [ABSTRACT FROM AUTHOR]