Development of a compact alpha and beta camera for dismantlement applications

Journal of Radioanalytical and Nuclear Chemistry - A new method has been developed to image surface contamination on-site by short range radiation emitters (such as alpha or beta particle...     

In situ migration of tritiated water and iodine in Grimsel granodiorite,part II: assessment of the diffusion coefficients by TDD modelling

Diffusive transport of iodine (I) and tritiated water (HTO) in granodiorite is studied in the framework of the long term diffusion project (LTD) at the Grimsel Test Site, Switzerland. In this paper we modelled the tracer profiles measured in a long term (780 days) in situ diffusion test was carried out as part of LTD. The main outcome of the modelling tends to prove that the in situ apparent diffusion coefficients of I and HTO are close to the reference apparent diffusion coefficient determined in the laboratory (D _a = 3 × 10⁻¹⁰ m² s⁻¹).

     

From Bq cm−3 to Bq cm−2 (and conversely)—part 2: useful dataset to apply the conversion to decommissioning operations

Journal of Radioanalytical and Nuclear Chemistry - A large set of key parameters is provided to use in decommissioning operations, the conversion method fully described in the companion paper...     

Diffusion of Tracer in Altered Tonalite: Experiments and Simulations with Heterogeneous Distribution of Porosity

Numerical time-domain-diffusion simulations were used for studying the diffusion behavior of tracer molecules in rock matrix with homogeneous and heterogeneous porosity. As the heterogeneous sample in these simulations, a 3D tomographic image of altered tonalite was used, in which the mineral components and the pores resolved by X-ray microtomography were represented by their respective intragranular porosities determined previously by the ¹⁴C-PMMA method. The apparent diffusion coefficient of a tracer in altered tonalite was determined experimentally, and was then used in the simulations. In the altered tonalite analyzed, inclusion of heterogeneity in the porosity increased the diffusion coefficient by 16 %. Altered and pristine feldspar was the main mineral component in the sample (72 %), and it also provided the dominant contribution to tracer diffusion, explaining alone 52 % of the diffusion coefficient. The large pores resolved by microtomography (6 %) and altered and pristine mica (22 %) gave an equal contribution to the diffusion coefficient. The simulation method applied was also validated by comparing the results to both an analytical and a numerical solution to the diffusion equation in a homogenous medium. In addition, the method was compared to discrete-time random-walk simulations in the case of randomly placed overlapping spheres.     

Construction of congested Csp3–Csp3 bonds by a formal Ni-catalyzed alkylboration

Through the combination of a Ni-catalyzed alkene alkenylboration followed by hydrogenation, the synthesis of congested Csp³–Csp³-bonds can be achieved. Conditions have been identified that allow for the use of both alkenyl-bromides and -triflates. In addition, the hydrogenation creates another opportunity for stereocontrol, thus allowing access to multiple stereoisomers of the product. Finally, the method is demonstrated in the streamlined synthesis of a biologically relevant molecule.

Through the combination of a Ni-catalyzed alkene alkenylboration followed by hydrogenation, the synthesis of congested Csp³–Csp³-bonds can be achieved.     

The Effect of Rock Matrix Heterogeneities Near Fracture Walls on the Residence Time Distribution (RTD) of Solutes

For interpreting solute transport experiments within rocks, the Residence Time Distributions (RTDs) of solutes in the rock matrix were either derived from the assumption of a homogeneous matrix, or were considered through analytical distributions of diffusion coefficients. A numerical approach based on a Lagrangian framework was developed in order to investigate the effect of spatial heterogeneities on RTDs. The matrix diffusion was simulated over two-dimensional computation grids, representing virtual or real digitized porosity maps. First, virtual porosity maps were used to mimic porous features linked to conductive fractures, such as (i) low-porosity coatings on fracture walls, and (ii) porosity gradients within the rock matrix. Furthermore, RTD was calculated for the real pore network of the Palmottu granite (Finland). It was shown that the arrangement of spatial heterogeneities located in the immediate vicinity of a conductive fracture modifies the RTD of solutes within the rock matrix. Porous zones located near fractures are of particular importance, because they generate anomalies on the RTD.     

From Bq cm−3 to Bq cm−2 (and conversely)—part 1: a useful conversion for autoradiography

Journal of Radioanalytical and Nuclear Chemistry - Autoradiography technique generally provides an image in cps cm?2, the conversion in Bq g?1 remaining a challenge. The Geant4...     

Fluorescence lifetime tomography of live cells expressing enhanced green fluorescent protein embedded in a scattering medium exhibiting background autofluorescence

We present a novel fluorescence lifetime tomography system applied to a highly scattering autofluorescent phantom containing live cells expressing the fluorophore enhanced green fluorescent protein (EGFP). The fluorescence signal was excited using a fiber-laser-pumped supercontinuum source and detected using wide-field time gating imaging. To facilitate rapid 3D reconstruction of the fluorescence lifetime distribution, the time-resolved data were Fourier-transformed in time to give complex functions that formed a data set for the Fourier domain reconstruction. Initially the presence of an unspecified background autofluorescence signal impeded reconstruction of the lifetime distribution, but we show that this problem can be addressed using a simple iterative technique.