Calculation of response parameters for a neutron long counter instrument.

The primary goal of this study was to develop a simulation model of a long counter available at Canadian Nuclear Laboratories (CNL). Using the Monte Carlo N-Particle version 6 (MCNP6) code, the model was used to calculate, as a function of incident energy, the number of counts recorded per source neutron, effective centre, and sensitivity. This study also carried out measurements of the neutron emission rate of and direct neutron flux at 2 m from an in-house 252Cf neutron source.

Characterization and mapping of the neutron fields around Bruce Power's 177Lu isotope production system.

Bruce Power operates a first-of-its-kind isotope production system (IPS) that enables continuous production of 177Lu within Canada Deuterium Uranium (CANDU) commercial power reactors. Located on the reactivity mechanisms deck of Unit 7, just outside of reactor containment but in close proximity to the primary heat transport (PHT) pumps, this facility offers unique advantages for 177Lu production. However, employees working in this area encounter a radiation hazard which consists primarily of photoneutrons. These originate from the base of the PHT pumps and are only present when the reactor is operating. This study evaluates neutron exposure at Bruce Power's IPS by using a nested neutron spectrometer (NNS) to determine the neutron energy spectra and absolute dosimetric quantities such as the ambient dose equivalent, H*(10). The results from the NNS are then compared to surveys performed by a portable neutron rem meter (Model NP-2 by Nuclear Research Corporation), routinely used by Bruce Power staff for workplace monitoring. While the Model NP-2 generally showed consistent results across locations, a 50% dose correction factor was identified when operators were harvesting 177Lu from the IPS. This finding highlights an opportunity to reduce the neutron dose that is assigned to operators when producing 177Lu.

Optimization and characterization of a coincidence beta-ray spectrometer.

Aimed at beta spectrometry and dosimetry for mixed beta-gamma fields, a Si-plastic scintillator coincidence beta-ray spectrometer has been developed. The spectrometer collects pure beta-ray spectra by rejecting the gamma-ray detection events through coincidence. Both pulse height and arrival time of each detection event were recorded in list mode by a compact digital processing system. Spectral measurements were carried out using mixed beta-gamma fields from 90Sr/90Y and 137Cs sources for various beta and gamma count rates to evaluate the system performance. Coincidence beta spectra were collected for four fixed beta count rates (7.3-241 cps) from 90Sr/90Y while the gamma count rate from 137Cs was varied from 500 to 8000 cps. The coincidence beta spectrum was stable and unperturbed by the gamma detection events for most measurements while notable perturbation was observed in the low energy region when the beta to gamma count ratio is very low.

A Pilot Study Measuring Aluminum in Bone in Alzheimer's Disease and control Subjects Using in vivo Neutron Activation Analysis.

Aluminum, being the most abundant metal in the earth's crust, is widely distributed in the environment, and is routinely taken up by the human body through ingestion and inhalation. Aluminum is not considered an essential element and it can be toxic in high concentrations. Most of the body burden of aluminum is stored in the bones. Aluminum has been postulated to be involved in the causality of Alzheimer's disease. A system for non-invasive measurement of bone aluminum using the in vivo neutron activation analysis technique has been developed and previously reported in the literature by our group. The results are reported as ratio of Al to Ca in order to eliminate the variations in beam parameters and geometry as well as the physical variations among the subjects such as size of the hand and bone structure. This pilot study included 30 subjects, 15 diagnosed with Alzheimer's disease in mild and moderate stages and 15 control subjects, all of whom were 60 years of age or older. The mean value of aluminum for the control group was 2.7±8.2µg Al/g Ca (inverse-variance weighted mean 3.5±0.9µg Al/g Ca) and for the Alzheimer's disease subjects was 12.5±13.1µg Al/g Ca (inverse-variance weighted mean 7.6±0.6µg Al/g Ca). The difference between the mean of the Alzheimer's disease group and the mean of the control group was 9.8±15.9µg Al/g Ca, with a p-value of 0.02. An age-dependent linear increase in bone aluminum concentration was observed for all subjects. The difference in serum aluminum levels between the two groups did not reach significance.

Characterization of neutron fields from bare and heavy water moderated (252)Cf spontaneous fission source using Bonner Sphere Spectrometer.

In this work a calibrated Bonner Sphere Spectrometer (BSS), together with ISO shadow cones, was used to quantify the total and scattered components of bare and heavy water moderated (252)Cf neutron fields. All measurements were performed with a BSS that was calibrated at the National Physical Laboratory (NPL), Teddington, UK, which is a global primary standard laboratory and world-leading facility for neutron metrology and neutron instruments calibration. The fields were characterized for source-spectrometer distances of 80, 100, 150 and 200cm; and at heights of 103 and 200cm from the facility floor. As expected, the scattered contribution was greatest at the farthest distance from the source and closer to the floor. Hence, at a distance of 200cm and a height of 103cm, the scatter added to the direct field up to 162% of the total neutron fluence and up to 61% of the ambient dose equivalent, while at the same distance and height of 200cm above the floor, these values were up to 146% and 52%, respectively. In the case of heavy water moderated (252)Cf neutron fields, a shadow cone subtraction technique could not be implemented, however Monte Carlo simulations were utilized in order to differentiate between the direct and scatter components of the neutron fields. In this case, at a source-detector distance of 200cm and a height of 103cm, the scatter added to the direct field up to 148% of the total neutron fluence and up to 45% of the ambient dose equivalent, while at the same distance and a height of 200cm above the floor, these values were up to 134% and 42%, respectively.

Monte Carlo model of HPGe detectors used in routine lung counting.

An MCNP model of a pair of planar HPGe detectors (designated as: detector 3 and detector 4), that are used for routine lung counting at AECL, was developed. The model was benchmarked against experimental results, where a multi-line (152)Eu source was counted in several different geometrical arrangements. The best agreement for both detectors was achieved when side and back dead layers (of both detectors) were quadrupled, with respect to the ones quoted by their manufacturer (Canberra). In the case of detector 4, the agreement between simulated and measured spectra was within 4%, throughout the whole γ-spectrum, spanning 70-1600 keV. The same was true for detector 3 at the lower end of the γ-spectrum. However, at the high end of the γ-spectrum, the agreement was within 7% and 12% for (152)Eu γ-lines at 778.9 and 1408.01 keV.

In vivo measurement of lead in the bones of smelter workers using the four-element 'clover-leaf' geometry detector system.

A total of 497 smelter employees from New Brunswick participated in a bone lead survey conducted by McMaster University in 2008 to examine the efficiency of lead exposure control programmes and a four-element 'clover-leaf' geometry detector system. Nearly 42% of the subjects had participated in both the previous surveys performed in 1994 and 1999. After developing the clover-leaf geometry system in 2006, the reliability of the system based on examining the consistency of four detectors and improving the minimum detection limit (MDL) was tested for the first time in 2008 by measuring lead levels of a large population that was occupationally exposed to lead. The Z test was used to study the distribution of the lead concentration calculated based on K(α) and K(ß) lead x-rays, where the results were broadly consistent with a normal distribution criterion, with relatively small means and standard deviations of between 1 and 2. The MDL of the clover-leaf geometry system was improved on average for tibia and calcaneus by a factor of 3.1 compared to the 1999 and 1994 surveys in which a conventional system (one detector) was used. Furthermore, by comparing the results of the three mentioned surveys, the 2008 results were found to represent the highest precision.