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With the complex composition of the radioisotopes and waste materials, the characterization of the volumetric low-level wastes from CANDU plants is challenging. This study presents a technique to localize and quantify the contaminations presented in the CANDU waste containers. MCNP-based models are developed for an N-type coaxial HPGe detector and a LaBr3 detector to simulate the photon peak information. The simulated efficiency and the experimental count rates are combined to estimate the activity of unknown waste samples. During the spectrum collection of a 4L Marinelli beaker source and 1-quart waste samples, the MCNP algorithm showed better accuracy in activity estimation than the Mirion ISOCS/LabSOCS software. With further development, this method has the potential to outperform the popular commercial software in estimating activity for volume sources with complex geometry and uneven distribution. The multi-detector array models with hotspot designs are also studied in this work to provide real-time information about the location and activity of the contamination inside the 2.2 m3 industrial low-level waste containers. The on-site measurements show promising results as the position of the contamination was able to be located within a volume of 61×40×34 cm. Overall, this technique has good potential to be utilized in the nuclear industry for large-volume low-level waste analysis. / Thesis / Master of Science (MSc)

The neutron-neutron (n-n) scattering length is a fundamental parameter in nuclear physics; however, measurements are plagued with large uncertainties caused by neutron detector cross talk. Many experimentalists also rely upon computer code to calibrate their neutron detectors. Experiments give one of two different numbers but there is still no adequate explanation for this discrepancy. We have developed a new neutron detector expressly for the purpose of improving the n-n scattering length measurement. It offers two important advantages: 1) minimal cross talk and 2) high counting efficiency. We calibrated the detector from 1 MeV to 6 MeV at 1 MeV increments. We have shown that the computer code, MCNP, does not always give the correct detector efficiency, and that reliance upon this code for calibration could be a large factor for error in previous experiments. Preliminary tests show no cross talk between two like detectors and suggest that these detectors in a n-n scattering length measurement.

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Gadolinium (Gd) is commonly used in contrast agents (GBCAs) to improve magnetic resonance imaging. GBCAs improve tumor imaging and were thought to be stable and clear from the body through excretion after administration. However, they have been found to dissociate and remain in organs such as the liver and kidneys. In these studies, a non-invasive Cd-109 based K x-ray fluorescence (K-XRF) “Clover-Leaf” detection system to study liver and kidney Gd levels was investigated to improve the minimum detection limit (MDL). Two Cd-109 sources, one with a relatively low activity of 0.78 GBq and a second high activity source of 5 GBq irradiated a human torso water phantom containing liver and kidney phantoms with Gd concentrations ranging from 0-100 ppm. The MDL was calculated from two different time measurements 5 hours (weak source) and 30 minutes (strong source). In addition, liver and kidney phantom measurements with overlaying tissue thicknesses from 6-26 mm were investigated. At present, the K-XRF detection system is able to detect the Gd in each phantom with both sources. The MDL for the liver and kidney with the weaker source is 2.95 ppm and 3.60 ppm, respectively. The MDL for the stronger source is 3.61 ppm and 3.87 ppm, respectively. The overlaying tissue thickness MDLs decreased exponentially since the thickness increased which increases the scattering and attenuation. Simulations with MCNP successfully modelled the experiments. MCNP simulations of the kidney with varying Gd concentrations in the cortex and medulla suggest that the XRF measurement is not sensitive to the Gd distribution in the phantom. To conclude, this detection system can measure Gd in liver and kidney phantoms and has low MDLs. Future work should focus on varying the detection capabilities, measuring the effects to the organs at risk, possible clinical trials, and improving the MCNP model and peak extraction. / Thesis / Master of Science (MSc)

This thesis describes XL, an x-ray imaging simulator for luggage inspection. This software system runs on a workstation and models x-ray sources, x-ray detectors and objects between them. A simple graphical interface permits the user to specify simulation parameters and inputs. XL then uses Monte Carlo methods to simulate x-ray interaction with matter, including the photoelectric effect, coherent scattering, and incoherent scattering. Finally, XL can produce x-ray images which agree closely with experimental data obtained from a commercial luggage scanner. The simulator will be a valuable tool in the development of future x-ray scanners, particularly those designed to detect explosives in luggage. / Master of Science

In the case of a radiological emergency it is of utmost importance that we can rapidly quantify theradionuclide content of a person or population to ensure that the right precautions or treatmentsare taken. In this project we investigate how well the Palmer geometry works to quantify the Cs-137 content of a test population. The aim is to find if this geometry could replace the currentmeasuring geometry. To begin with, we investigate the full energy peak efficiencies in the Palmer geometry formeasurements of whole body content of radioactive nuclides using Detective-X, a spectrometricgamma radiation detector produced by ORTEC. First, we perform an empirical efficiency cali-bration based on measurements with the phantom IRINA using both Cs-137 and Eu-152 to cover arange of energies. We employ two configurations of the IRINA phantom to represent the bodyof the average woman and man in Sweden. The detector is directed towards the abdomen of the phantom, which is in a crouched seated position, to emulate the Palmer geometry. Additionally, we construct a detector model in Monte-Carlo N-particle transport code (MCNP).To validate this model we calibrate the detector with a Cs-137 point source at various angles of in-cidence to determine its angular dependence, performing the measurements along two axes ofrotation. We find that the efficiency in the final MCNP model agree well with the empiricalcalibration. The detector model is then used alongside the MCNP models of two IRINA configurations to compare the simulated and empirical calibrations. We observe that the detector model agree well with our empirical calibrations. Finally, we measure the whole body content of Cs-137 in a group of residents around Umeå,Sweden. In these measurements, the Palmer geometry is employed, where the test person sitswith the detector in their lap, having the top cap against their stomach, and crouches over it. These measurement are compared to those taken in a low background setup (mobile whole body counter), where the test person lays down on their back in a lead cradle and have their legs and head above their chest and abdomen. We find that the signal in the Palmer geometry has a higherbackground level, preventing detection of low activities. Additionally, the Palmer setup tends to underestimate the activity compared to the current setup. More test subjects with higher activity is needed to test the setup, as the current data is not sufficient for definite conclusions. In conclusion, the simulation model is sufficient for future simulations of the Palmer geometry. The tests of the Palmer geometry are not sufficient to sufficiently prove if the geometry will be a good method to determine the whole body content of radionuclides. To test it further a larger test population with a higher activity is needed. The calibrations should also be done with other configurations of IRINA and activity distribution to better emulate an adult human.