Managing children during a radiological or nuclear emergency--Canadian perspectives.

Children have a higher chance of being contaminated by radioactive materials during a radiological or nuclear (RN) emergency. They are more sensitive to radiation health effects and suffer more significant psychosocial impacts than adults during emergency response. This paper presents a summary of recommendations on effective management of children during an RN emergency. These recommendations intend to be additional considerations for existing RN response protocols and procedures implemented at local, state/provincial, or national level.

Counting 241Am in the BfS human skull phantom on contact-evaluation in the human monitoring laboratory.

Skull counting can be used to assess the activity of radionuclides internally deposited in the bone. The Human Monitoring Laboratory (HML) at Health Canada conducted the measurement of 241Am in the BfS (Bundesamt für Strahlenschuts) skull phantom on contact with the skull for various positions. By placing the detector in contact, the HML can improve the counting efficiency by over 20% compared to placing the detector 1 cm above the surface of the skull. Among all the positions tested, the forehead position is the preferred counting geometry due to the design of HML's counting facility and the comfort it would provide to the individual being counted, although this counting position did not offer the highest counting efficiency for the gamma rays (either the 59.5 keV or the 26.3 keV) emitted by 241Am.

Modeling population screening process for maximizing throughputs.

Following a large-scale radiation emergency, affected populations will need to be screened soon after for potential contamination (external or internal). Effective management of the available resources can help maximize the screening throughputs. This paper reports the modeling results for screening throughputs in a population screening center using a set resource, considering two major variables, the arrival rate (number of people arriving at the screening center per minute) and the contamination probability (the probability of finding a contaminated group). Both the full process (including all sub-processes in a population screening center) and the core process (including only the screening sub-processes: pre-screening, portal monitoring, and whole body counting) were simulated. As expected, for both processes, as the arrival rate increases, the screening center can get overwhelmed. Interestingly, the contamination probability becomes a significant factor for screening throughputs only when the arrival rate becomes high. The results show that following an emergency, when the arrival rate is high, much more resources will need to be deployed to the population screening center or multiple screening centers will need to be established.

Evaluation of a commercial software package's ability to calibrate an in vivo counter for emergency response.

A commercial detector calibration package has been assessed for its use to calibrate the Human Monitoring Laboratory's Portable Whole Body Counter that is used for emergency response. The advantage of such a calibration software is that calibrations can be derived very quickly once the model has been designed. The commercial package's predictions were compared to experimental point source data and to predictions from Monte Carlo simulations. It was found that the software adequately predicted the counting efficiencies of a point source geometry to values derived from Monte Carlo simulations and experimental work. Both the standing and seated counting geometries agreed sufficiently well that the commercial package could be used in the field.

Evaluation of Ludlum Corporation's portable portal monitor and comparison with the HML'S existing portal monitors.

Since the Human Monitoring Laboratory compared two types of portal monitors (the P3 and the MiniSentry) that could be field deployed in response to an emergency, two more brands have been added to the inventory. This paper summarizes a comparison of the capabilities of the previous portal monitors with the two additions: the Thermo Eberline TPM-903B and the Ludlum 52-1-1. The comparison shows that none of the portals greatly exceed the others in capability, but that each will have their place during emergency deployment; however, when beta radiation or low energy gamma radiation is suspected, then the best choice would be the Ludlum 52-1-1.

Lung counting: comparison of detector performance with a four detector array that has either metal or carbon fibre end caps, and the effect on mda calculation.

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 (152)Eu 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.

Comparison of two leg phantoms containing (241)Am in bone.

Three facilities (CIEMAT, HMGU and HML) have used their in vivo counters to compare two leg phantoms. One was commercially produced with (241)Am activity artificially added to the bone inserts. The other, the United States Transuranium and Uranium Registries' (USTUR) leg phantom, was manufactured from (241)Am-contaminated bones resulting from an intake. The comparison of the two types of leg phantoms showed that the two phantoms are not similar in their activity distributions. An error in a bone activity estimate could be quite large if the commercial leg phantom is used to estimate what is contained in the USTUR leg phantom and, consequently, a real person. As the latter phantom was created as a result of a real contamination, it is deemed to be the more representative of what would actually happen if a person were internally contaminated with (241)Am.

Quantification of 235U and 238U activity concentrations for undeclared nuclear materials by a digital gamma-gamma coincidence spectroscopy.

The purpose of this study is to investigate the possibility of verifying depleted uranium (DU), natural uranium (NU), low enriched uranium (LEU) and high enriched uranium (HEU) by a developed digital gamma-gamma coincidence spectroscopy. The spectroscopy consists of two NaI(Tl) scintillators and XIA LLC Digital Gamma Finder (DGF)/Pixie-4 software and card package. The results demonstrate that the spectroscopy provides an effective method of (235)U and (238)U quantification based on the count rate of their gamma-gamma coincidence counting signatures. The main advantages of this approach over the conventional gamma spectrometry include the facts of low background continuum near coincident signatures of (235)U and (238)U, less interference from other radionuclides by the gamma-gamma coincidence counting, and region-of-interest (ROI) imagine analysis for uranium enrichment determination. Compared to conventional gamma spectrometry, the method offers additional advantage of requiring minimal calibrations for (235)U and (238)U quantification at different sample geometries.

Design and testing of a new stand for the BOMAB family of phantoms.

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.

Measuring an 'active person' with the HMLs emergency response instruments.

The Human Monitoring Laboratory has had a unique opportunity to measure two volunteers who had received (99m)Tc-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 (99m)Tc-methyl diphosphonate was not a good predictor of that person's metabolism.

HML's whole body counter: measuring highly radioactive persons.

The National Internal Radiation Assessment Section's Human Monitoring Laboratory (HML) has the responsibility to measure persons who may become internally contaminated following an accidental or intentional release of radioactivity. In preparation for measuring individuals who may be highly internally contaminated, the HML has reconfigured and recalibrated its whole body counter for this event. The calibration was performed using Monte Carlo simulations and validated by experimental measurements. An equation was developed that related the counting efficiency as a function of photon energy and phantom-to-detector distance. The equation could predict efficiencies to within 10% or better. Dead time problems, as a result of high internal activities, have been minimized by having a variety of counting positions. Six example nuclides have been used (Co, Co, Y, Ba, Cs, and Am) to show what is achievable and what is not.

Recalibration of the Cameco mobile lung counter.

The Cameco lung counter has been recalibrated using the Lawrence Livermore National Laboratory torso phantom using an extended lung set (i.e., longer than the original set). The previous calibration had used the Japanese Atomic Energy Research Institute torso phantom. The new calibration had lower counting efficiencies and, as a result, higher minimum detectable activities. The recalibrated Cameco lung counter was used to measure an extended lung set that had the volume reduced by using modified planar inserts for the sliced lungs as the extended lung set has a lung volume that is larger than Reference Man. This work has shown that sliced lungs can be used to alter the characteristics of the phantom's lung inserts substantially and provide flexibility in measurements previously not recognized.

Anatomy of and lessons learned from a Canadian national-scale radiological exercise: ExIT-08.

Exercise Initial Thunder (ExIT-08) was the fourth in a series of four emergency response exercises sponsored by the Chemical, Biological, Radiological, Nuclear and Explosives Research and Technology Initiative (CRTI). It was designed to test the Canadian Federal, Provincial and Municipal response to a terrorist attack using radioactive materials. The complexity of this exercise had been increased over previous exercises to now include provincial and municipal players. As a result about 350 persons participated as players in the 4-day exercise that was held in two locations in the western part of Canada. This paper summarizes the experiences and the lessons learned of the Health Canada (HC) team.

A methodology for improving throughput using portal monitors.

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.

A field deployable high-resolution urine gamma analyzer.

The Human Monitoring Laboratory has extended the use of its portable whole body counters to portable gamma spectrometers for urinalysis. The protocol tested measured a 120-mL sample in a polypropylene sample container for 5 min. Minimum detectable activities were estimated for 241Am, 57Co, 137Cs, and 60Co. The former is 113 Bq per sample, and the latter three are between 27-29 Bq per sample. Assuming an intake 5 d before the measurement, and all other parameters as default, the committed effective doses are 517 Sv, 76 muSv, 402 muSv, and 1.5 mSv, respectively. Clearly, this instrument can be used as a field deployable gamma spectrometer for urinalysis for activation and fission products, but actinides (and other low energy photon emitters) remain problematic.

Retrospective determination of the contamination in the HML's counting chambers.

The original documentation surrounding the purchase of the Human Monitoring Laboratory's (HML) counting chambers clearly showed that the steel contained low levels of radioactivity, presumably as a result of A-bomb fallout or perhaps to the inadvertent mixing of radioactive sources with scrap steel. Monte Carlo simulations have been combined with experimental measurements to estimate the level of contamination in the steel of the HML's whole body counting chamber. A 24-h empty chamber background count showed the presence of 137Cs and 60Co. The estimated activity of 137Cs in the 51 tons of steel was 2.7 kBq in 2007 (51.3 microBq g(-1) steel) which would have been 8 kBq at the time of manufacture. The 60Co that was found in the background spectrum is postulated to be contained in the bed-frame. The estimated amount in 2007 was 5 Bq and its origin is likely to be contaminated scrap metal entering the steel production cycle sometime in the past. The estimated activities are 10 to 25 times higher than the estimated minimum detectable activity for this measurement. These amounts have no impact on the usefulness of the whole body counter.

BOMAB phantom variability: do small dimensional changes matter?

The Human Monitoring Laboratory (HML) has had a number of BOMAB phantoms built over the years. Upon characterization, it has been found that the dimensions of the phantoms are always slightly different. This study has looked at the effect of these small variances in dimensions of the phantoms and compared the results to what is required in the industry standard using Monte Carlo simulations for three counting geometries: the HML's scanning detector whole body counter, the StandFast whole body counter, and the W-chair whole body counter. It has been found that the effect of these small variations on the performance of these phantoms is very minor (<5%). It is reassuring to find that small variations in manufacturing, even if individual sections are non-compliant, have such a minor effect on performance as to be considered a negligible effect for any counting system's geometry.

Can the HML's sliced BOMAB phantom be used in any whole body counter with a reduced number of sources?

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, 1 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.

Effect of an aerosol deposition pattern in the lung on the counting efficiency of a large area germanium detector array.

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 ( approximately 60 keV), the effect of the heterogeneous distribution is greatly reduced and errors in the activity estimate reduced to approximately 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 2sigma) as heterogeneous by two of the four detectors in the counting array.

The Human Monitoring Laboratory's whole body counter: monitoring the liquid nitrogen level as a quality control tool.

The Human Monitoring Laboratory (HML) has developed a method to measure the liquid nitrogen boil-off rate from the whole body counter's single dewar as a function of time. The device consists of a commercially available instrument that was modified to fit the HML's whole body counter's dewar; unfortunately, the modification was not perfect requiring an alternative approach to using the maximum fill value. The boil-off rate is now measured by taking two measurements and calculating the loss rate. Resulting boil-off rates are plotted on a control chart so that long-term trends can be easily assessed.