Comparison of phosphor screen autoradiography and micro-pattern gas detector based autoradiography for the porosity of altered rocks

Abstract

this study aims to further develop the 14 c-pMMA porosity calculation method with a novel autoradiography technique, the Micro-pattern gas detector autoradiography (MpGDA). in this study, the MpGDA is compared with phosphor screen autoradiography (SpA). A set of rock samples from Martinique island exhibiting a large range of connected porosities was used to validate the MpGDA method. calculated porosities were found to be in agreement with ones from the SpA and the tripleweight method (TW). The filmless nature of MPGDA as well as straightforward determination of C-14 radioactivity from the source rock makes the porosity calculation less uncertain. The real-time visualization of radioactivity from C-14 beta emissions by MPGDA is a noticeable improvement in comparison to SpA. Autoradiography has demonstrated its adaptability and reliability in several research areas. With regard to the development of autoradiographic techniques the very first autoradiograph was obtained by Becquerel in 1896, through exposition of an emulsion of silver halide crystals in contact with radioactive material 1. Autoradiographic techniques allow the production of spatial distribution of radioactivity in the material; the sample itself being the source of the radioactivity either as occurring naturally in the material or as artificially added radioactivity. In the case of geological samples, 238 U, 232 Th and 40 K bearing minerals are the main sources of natural radioactivity 1. The radioactive source may also be in the form of an artificial radioactive marker, such as 3 H or 14 C labelled methylmethacrylate (MMA) 2-4. Investigated samples are impregnated with the radiolabeled tracer and fixed in place via polymerization of the marked MMA in the connected pore network of rock samples. Thus, the image of the connected pore network can be produced by exposing the impregnated sample surface on a photographic film. This brief description corresponds to the 14 C polymethylmethacrylate (14 C-PMMA) autoradiography method 2-4 and will be used for porosity analysis in this work. In the field of nuclear waste management, the 14 C-PMMA method has been successfully applied to investigate the connected pore network of geological materials, radioelements diffusion within rock matrices and relations between the porosity and mineralogy of rocks 5-8. In the biological field, injecting the radioligands into living tissues allows to map the anatomical location of specific receptors by autoradiographic techniques. For instance, Larsson & Ullberg 9 introduced a new autoradiographic technique, the whole body macro autoradiography (WBA), allowing to study the distribution of 35 S-labelled penicillin in a rat using entire frozen sections of them after injection of radiolabeled tracer. In drug distribution studies, Young and Kuhar 10 were able to localize opioid receptors in a rat brain by 14 C, 3 H, 125 I and 35 S, and more recently, Fang et al. 11 studied the effect of cocaine, ketamine and methamphetamine on dopamine terminals in the striatum of rats using 18 ...

Improved Radio-Cesium Detection Using Quantitative Real-Time Autoradiography

“…These values could then be cross-referenced to other studies (e.g., efficiency for carbon-14 = 36% and efficiency for barium-133 = 82.1%) to evaluate the validity of this method. 35,38 Our study also evaluated the critical level L C , detection limit N D , and minimum detectable activity MDA per unit area for the detection of radio-Cs using the BeaQuant system. The blank sample was used to acquire the background counts from the detector.…”

“…For such techniques, the autoradiograph can be immediately seen during the measurement and the sample’s radioactivity can be gauged without stopping the acquisition. In contrast to phosphor screen autoradiography, which provides an image that is indirectly measured by the photo-stimulated luminescence of the imaging plate, real-time autoradiographs construct the image by directly measuring the individual decay emitted from the sample . Due to the low density and thickness of the active gas media, MPGDs are largely insensitive to γ radiation at room temperature and atmospheric pressure.…”

Weathering of Viamão granodiorite, south Brazil: Part 2 – Initial porosity of un-weathered rock controls porosity development in the critical zone

“…To quantify the connected porosity of the rock at different stage of weathering with a spatial resolution of ~20 µm, the samples were impregnated with the 14 C-MethylMethAcrylate (MMA) liquid monomer (Siitari-Kauppi, 2002;Oila et al, 2005;Sardini et al, 2006Sardini et al, , 2009Mazurier et al, 2016;Bonnet et al, 2020;Delayre et al, 2020). The unweathered rock (GRV01), saprock (GRV03, GRV04) and saprolite (VIA03) samples were dried in a vacuum in an oven set at 50 • C for 11 days to remove all residual water before impregnation.…”

Chemical and Microstructural Properties of Designed Cohesive M-S-H Pastes

“…Finally, the activities are converted into porosities by taking into account the beta attenuation and the true density of the samples (measured by helium pycnometry) [57]. Several PMMA standards of known C-14 activities are needed to convert the grey values of each pixel into porosity values [57][58][59][60]. The uncertainty of the C-14-PMMA autoradiography has been empirically determined to be approximately 10% [57].…”