Total filterable mercury and 210Pb in the Canadian Arctic air.

Total filterable mercury (TFM) and lead-210 ((210)Pb) were measured for a one-year air particulate sample series collected weekly at Resolute (74.7 degrees N, 95.0 degrees W), a Canadian high Arctic site, during July 1999 and June 2000. The measurements showed a clear time lag of two months between the peak concentrations of TFM and (210)Pb.

The NORMAN phantom vs. the BOMAB phantom: are they different?

This paper describes the implementation of the NORMAN phantom with the Human Monitoring Laboratory's Monte Carlo simulator, the problems that were encountered, and their solution. The NORMAN phantom has been compared with the reference man BOMAB phantom in three different whole body counting geometries: a scanning detector system (WBC1), and two stand-up whole body counters (WBC2, WBC3) that have different reference points for their counting geometry. The average agreement (taken over all energies) of the two phantoms is approximately a factor of 1.15 on any given counting system. For the first two systems (WBC1, WBC2) the BOMAB has the highest counting efficiency, whereas it is reversed on the third system (WBC3). Considering the differences between the two phantoms, the agreement is good.

Comparison of the St. Petersburg phantom with a BOMAB phantom in the ORTEC StandFast whole body counter: a Monte Carlo simulation.

Three sizes of the St. Petersburg phantom have been compared to six sizes of BOMAB phantoms measured by a virtual StandFast whole body counter using Monte Carlo simulations to investigate if the counting efficiencies are equivalent. This work shows that previously published data comparing the Reference Man sized phantom at 662 keV is supported; however, the simulations also show that the smaller sized St. Petersburg phantoms do not agree well with BOMAB phantoms. It is concluded that, compared with BOMAB phantoms, the St. Petersburg phantoms are system dependent and that they should be validated over a wide photon energy range against corresponding BOMAB phantoms prior to their use for calibrating whole body counters.

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.

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.

Monte Carlo comparison of the St Petersburg phantom with a BOMAB phantom in the HML's whole-body counter.

Three sizes of the St Petersburg phantom have been compared to six sizes of BOMAB phantoms measured by a virtual whole-body counter similar to the one in use in the Human Monitoring Laboratory using Monte Carlo simulations. The previously published data comparing the St Petersburg Reference Man sized phantom with a similar sized Bottle Manikin Absorber Phantoms (BOMAB) phantom at 662 keV is supported; however, the simulations also show that the smaller sized St Petersburg phantoms do not agree well with smaller BOMAB phantoms. It is concluded that the St Petersburg phantoms are system dependent meaning that all sizes of the St Petersburg phantoms should be experimentally compared over a wide photon energy range against corresponding BOMAB phantoms to validate their use for calibrating whole-body counters.

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.

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.

Fundamental uncertainties in lung counting.

The HML has investigated the effect the uncertainty introduced into an activity estimate from a lung count due to 1) replicate counts and 2) lung set variability. Replicate counts in the HML seem to only be affected by random statistics as the uncertainty can be predicted by Monte Carlo simulations. These findings from the lung set variability experiments suggest that a lung set has an unquantified uncertainty on its activity that adds a component to the uncertainty on the counting efficiency, and ultimately the activity estimate, as they can differ by as much as 30% at 17.5 keV or about 13% at 185.7 keV, when one is expecting only a 3% difference.

The LLNL voxel phantom: comparison with the physical phantom and previous virtual phantoms.

The Human Monitoring Laboratory has created a voxel phantom from computer tomography scans of the Lawrence Livermore National Laboratory (LLNL) torso phantom for use in Monte Carlo simulations. The voxel phantom has been compared to the previously developed mathematical phantom using Monte Carlo simulations and both virtual phantoms have been compared to physical measurement of the LLNL phantom. The voxel phantom agreed well with the others, except at very low photon energies (i.e., 17.5 keV), with predicted counting efficiencies being within 2% of the counting efficiencies from the other two phantoms at 59.5 keV and above. The mathematical phantom performs similarly to the voxel phantom, but much faster, so it is an excellent alternative if computer power is lacking. The voxel phantom of the LLNL phantom is available from the authors, on request.

The standfast whole body counter and the sliced BOMAB phantom: efficiency as a function of number of sources and energy modeled by MCNP5.

Previously, using Monte Carlo simulations, this laboratory conceptualized a new phantom: the sliced Bottle Manikin Absorber (BOMAB) phantom. It was intended for calibration or performance testing of whole body counters and the HML subsequently built and tested that phantom. Also, this laboratory tested another phantom used for the calibration of the StandFast whole body counter and identified some deficiencies. This paper investigates the use of the sliced BOMAB phantom as an alternative for the calibration of the StandFast and shows how the 165 sources required for a full loading of the sliced BOMAB can be reduced to a much smaller number without compromising the calibration. The agreement of the sliced BOMAB with eight sources is approximately 1% when compared with a conventional BOMAB phantom.

The StandFast whole body counter: efficiency as a function of BOMAB phantom size and energy modeled by MCNP5.

The StandFast whole body counter has been modeled using Monte Carlo simulations to examine the effect of phantom size, photon energy, and position of the phantom within the counting enclosure on the counting efficiency. The first geometry, the manufacturer's recommended positioning, was found to have the higher counting efficiencies and the most dependence on phantom size. The second position, where the phantom is at the back of the counting enclosure, had lower counting efficiencies, and hence higher minimum detectable activities, by a factor of between 1.3 to 2.1 when compared with the first geometry; however, for emergency response where accuracy is to be preferred over sensitivity, this geometry would be the better choice. A unified calibration equation was also developed for the StandFast so that it is possible to predict the counting efficiency as a function of photon energy and size to within 11%.

Evaluation of two commercially available portal monitors for emergency response.

The Human Monitoring Laboratory has compared two types (the P3 and the MiniSentry) of portal monitors that can be field deployed in response to an emergency. They can be used to screen persons for internal or external radioactive contamination by fission activation products (neither unit is capable of detecting alpha or beta radiation, and the amount of material required to alarm the monitors is unacceptably high for low energy x rays or gamma rays) following an incident involving the release of radioactive material (accidental or intentional). It was found that the P3 benefits from simplicity but requires slightly more activity to alarm than the MiniSentry, although for emergency response, the amount of activity that can be detected is far below a level where significant health effects will occur. The MiniSentry was found to have more capability than the P3, but these benefits also bring their own disadvantages. It was also found that the MiniSentry would be difficult to deploy in an outdoor setting whereas the P3 is well designed for a field setting. Despite the differences found, the HML has concluded that both have a distinct place in emergency monitoring. In the future, the HML plans to have both instruments ready for field deployment.

Exercise Maritime Response (EXMR): lessons learned for population monitoring and communications.

Exercise Maritime Response was the third in a series of four emergency response exercises sponsored by the Chemical, Biological, Radiological and Nuclear Research and Technology Initiative. 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 simulated contaminated members of the public. This paper summarizes the experiences, and the lessons learned, of the Health Canada (HC) team. The largest issues identified by the HC team were: crowd control, insufficiency of staff to deal with surge capacity, and communications. The exercise did prove that the population monitoring equipment worked well and that small amounts of radioactivity were easily identified and quantified to within 20% of their true value.

The efficiency curve: a new function.

Working from first principles, an efficiency curve function has been developed by considering the physics of photon transport through matter. The function has been compared to other function in popular usage and been found to fit the data better especially about the knee of the curve. The main disadvantage of the new function is that it is data hungry, but this can be overcome by use of Monte Carlo simulations.

Large area germanium detector arrays for lung counting: what is the optimum number of detectors?

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 MDA 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 approximately 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.

Are Portable Personnel Portal Monitors too sensitive?

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.

A commentary on some inconsistencies in the icrp 2005 recommendations: exclusion levels.

The International Commission on Radiological Protection (ICRP) 2005 Recommendations, which were released at the International Radiation Protection Association's congress held in Madrid (May 2004), have been available for public comment via the ICRP's Web site. The comment period has now closed and the Recommendations are presumably being re-worked. There are several inconsistencies in the Recommendations and they are exemplified by looking at the exclusion levels in more detail. The relevant text of the Recommendations is included in this paper as an . It is suggested that the International Atomic Energy Agency's approach is more balanced where each nuclide receives its own exclusion level instead of the incomplete and arbitrary categories proposed by the ICRP.

The sliced bomab phantom: a new variant for intercomparison.

Previously, this laboratory conceptualized a new phantom for calibration or performance testing of whole body counters using Monte Carlo simulations. This paper describes the physical reality that was created from the Monte Carlo design project and compares its counting efficiency to that of a conventional BOMAB phantom using two whole body counters. In one counter (NaI based) the agreement between the two phantoms was +/-8% and in the second counter (Ge based) the agreement was +/-5% at all the energies measured (126 keV, 661 keV, 1172 keV, 1330 keV). The advantage of the sliced phantom is that the sources are solid, sealed, and cannot leak activity thereby simplifying packing for shipment if the phantom is classified as a Dangerous Good. The new phantom is, therefore, ideal for uses that involve shipment, such as an intercomparison exercise. The phantom is also re-usable as the sources can be changed.

Sensitivity of portable personnel portal monitors: potential problems when dealing with contaminated persons.

Health physicists are usually concerned with small amounts of radioactivity and strive to develop techniques to measure them; however, following a terrorist attack involving radioactive materials the converse might be the case, and exposed persons may be heavily contaminated. The Human Monitoring Laboratory (HML) has field tested its Portable Personnel Portal (P3) monitors using sources up to 1,700 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 crowd control techniques.