Efficient microplastics extraction from sand. A cost effective methodology based on sodium iodide recycling.

Evaluating the microplastics pollution on the shores requires overcoming the technological and economical challenge of efficient plastic extraction from sand. The recovery of dense microplastics requires the use of NaI solutions, a costly process. The aim of this study is to decrease this cost by recycling the NaI solutions and to determine the impact of NaI storage. For studying the NaI recyclability, the solution density and the salt mass have been monitored during ten life cycles. Density, pH and salt mass have been measured for 40days to assess the storage effect. The results show that NaI solutions are recyclable without any density alterations with a total loss of 35.9% after the 10cycles of use. During storage, chemical reactions may appear but are reversible. Consequently, the use of recycling methods allows for a significant cost reduction. How far the plastic extraction by dense solutions is representative is discussed.

Applicability of self-activation of an NaI scintillator for measurement of photo-neutrons around a high-energy X-ray radiotherapy machine.

The applicability of the activation of an NaI scintillator for neutron monitoring at a clinical linac was investigated experimentally. Thermal neutron fluence rates are derived by measurement of the I-128 activity generated in an NaI scintillator irradiated by neutrons; ß-rays from I-128 are detected efficiently by the NaI scintillator. In order to verify the validity of this method for neutron measurement, we irradiated an NaI scintillator at a research reactor, and the neutron fluence rate was estimated. The method was then applied to neutron measurement at a 10-MV linac (Varian Clinac 21EX), and the neutron fluence rate was estimated at the isocenter and at 30 cm from the isocenter. When the scintillator was irradiated directly by high-energy X-rays, the production of I-126 was observed due to photo-nuclear reactions, in addition to the generation of I-128 and Na-24. From the results obtained by these measurements, it was found that the neutron measurement by activation of an NaI scintillator has a great advantage in estimates of a low neutron fluence rate by use of a quick measurement following a short-time irradiation. Also, the future application of this method to quasi real-time monitoring of neutrons during patient treatments at a radiotherapy facility is discussed, as well as the method of evaluation of the neutron dose.

Monte Carlo simulations of NaI(Tl) spectra for measurements of semi-infinite plumes.

For the past 10 y Health Canada has operated a Fixed Point Surveillance Network of NaI(Tl) detectors across Canada. Deployed for both emergency response and daily monitoring of airborne radiation in the environment, a spectral stripping method allowed measurement of certain isotopes well below the ambient dose rate. These include (133)Xe, (135)Xe and (41)Ar, typical of emissions from operating nuclear reactors. In an effort to increase the number of isotopes measured at these low levels a new technique of spectral fitting using spectral templates is being implemented. However, this requires very accurate spectral templates that can be difficult or impossible to obtain empirically for environmental measurements of airborne radio-isotopes. Therefore, a method of efficiently using Monte Carlo techniques to create these templates was developed.

Assessing internal contamination after the detonation of a radiological dispersion device using a 2x2-inch sodium iodide detector.

The detonation of a radiological dispersion device may result in a situation where individuals inhale radioactive materials and require rapid assessment of internal contamination. The feasibility of using a 2×2-inch sodium-iodide detector to determine the committed effective dose to an individual following acute inhalation of gamma-emitting radionuclides was investigated. Experimental configurations of point sources with a polymethyl methacrylate slab phantom were used to validate Monte Carlo simulations. The validated detector model was used to simulate the responses for four detector positions on six different anthropomorphic phantoms. The nuclides examined included (241)Am, (60)Co, (137)Cs, (131)I and (192)Ir. Biokinetic modelling was employed to determine the distributed activity in the body as a function of post-inhalation time. The simulation and biokinetic data were used to determine time-dependent count-rate values at optimal detector locations on the body for each radionuclide corresponding to a target committed effective dose (E50) value of 250 mSv.

A simple well-logging tool using boron-lined sodium iodide scintillators and an 241Am-Be neutron source.

A couple of 2-inch by 2-inch right cylinder sodium iodide scintillators and an Am-Be radioisotope neutron source have been used in a neutron porosity well-logging tool to explore the variation of hydrogen contents in a prototype formation. Both Monte Carlo N-particle transport code simulation and experimental results of the near- to far-detector responses confirm the reliable sensitivity of proposed tool to the formation porosity.

Accurate Monte Carlo modelling of the back compartments of SPECT cameras.

Today, new single photon emission computed tomography (SPECT) reconstruction techniques rely on accurate Monte Carlo (MC) simulations to optimize reconstructed images. However, existing MC scintillation camera models which usually include an accurate description of the collimator and crystal, lack correct implementation of the gamma camera's back compartments. In the case of dual isotope simultaneous acquisition (DISA), where backscattered photons from the highest energy isotope are detected in the imaging energy window of the second isotope, this approximation may induce simulation errors. Here, we investigate the influence of backscatter compartment modelling on the simulation accuracy of high-energy isotopes. Three models of a scintillation camera were simulated: a simple model (SM), composed only of a collimator and a NaI(Tl) crystal; an intermediate model (IM), adding a simplified description of the backscatter compartments to the previous model and a complete model (CM), accurately simulating the materials and geometries of the camera. The camera models were evaluated with point sources ((67)Ga, (99m)Tc, (111)In, (123)I, (131)I and (18)F) in air without a collimator, in air with a collimator and in water with a collimator. In the latter case, sensitivities and point-spread functions (PSFs) simulated in the photopeak window with the IM and CM are close to the measured values (error below 10.5%). In the backscatter energy window, however, the IM and CM overestimate the FWHM of the detected PSF by 52% and 23%, respectively, while the SM underestimates it by 34%. The backscatter peak fluence is also overestimated by 20% and 10% with the IM and CM, respectively, whereas it is underestimated by 60% with the SM. The results show that an accurate description of the backscatter compartments is required for SPECT simulations of high-energy isotopes (above 300 keV) when the backscatter energy window is of interest.

Ion specific protein assembly and hydrophobic surface forces.

Large anions are attracted to hydrophobic surfaces while smaller, well solvated ions are repelled. Using a combination of explicit solvent and continuum model simulations we show that this leads to significant ion-specific protein-protein interactions due to hydrophobic patches on the protein surfaces. In solutions of NaI and NaCl we calculate the potentials of mean force and find that the resulting second virial coefficients for lysozyme correspond well with experiment. We argue that ionic interactions with nonpolar surface groups may play an important role for biomolecular assembly and Hofmeister-type effects.

Calculation of total counting efficiency of a NaI(Tl) detector by hybrid Monte-Carlo method for point and disk sources.

This paper presents results on the total gamma counting efficiency of a NaI(Tl) detector from point and disk sources. The directions of photons emitted from the source were determined by Monte-Carlo techniques and the photon path lengths in the detector were determined by analytic equations depending on photon directions. This is called the hybrid Monte-Carlo method where analytical expressions are incorporated into the Monte-Carlo simulations. A major advantage of this technique is the short computation time compared to other techniques on similar computational platforms. Another advantage is the flexibility for inputting detector-related parameters (such as source-detector distance, detector radius, source radius, detector linear attenuation coefficient) into the algorithm developed, thus making it an easy and flexible method to apply to other detector systems and configurations. The results of the total counting efficiency model put forward for point and disc sources were compared with the previous work reported in the literature.

Optimizing Compton camera geometries.

Compton cameras promise to improve the characteristics of nuclear medicine imaging, wherein mechanical collimation is replaced with electronic collimation. This leads to huge gains in sensitivity and, consequently, a reduction in the radiation dosage that needs to be administered to the patient. Design modifications that improve the sensitivity invariably compromise resolution. The scope of the current project was to determine an optimal design and configuration of a Compton camera that strikes a balance between these two properties. Transport of the photon flux from the source to the detectors was simulated with the camera geometry serving as the parameter to be optimized. Two variations of the Boltzmann photon transport equation, with and without photon polarization, were employed to model the flux. Doppler broadening of the energy spectra was also included. The simulation was done in a Monte Carlo framework using GEANT4. Two clinically relevant energies, 140 keV and 511 keV, corresponding to 99mTc and 18F were simulated. The gain in the sensitivity for the Compton camera over the conventional camera was 100 fold. Neither Doppler broadening nor polarization had any significant effect on the sensitivity of the camera. However, the spatial resolution of the camera was affected by these processes. Doppler broadening had a deleterious effect on the spatial resolution, but polarization improved the resolution when accounted for in the reconstruction algorithm.