Fission-Track Ages and Track-Annealing Behavior of Some Micas

Measurements of alpha radioactivity in thermal power plant effluents employing CR-39 detector based improved alpha track detection method

Natural radioactivity is released into the environment during the combustion process of coal at various thermal power plants. Coal contains higher contents of α-emitting radionuclides such as ²³⁸U, ²³²Th along with their decay elements, which pose a potential health risk to the population. In the present studies, the effluent waste samples were collected from a coal fired Thermal Power Plant. Samples were collected in the form of solid residues and filtrates. CR-39 detector pieces were then exposed for varying time with residue and filtrate samples for registering the alpha tracks for α-detection and measurement. Thus, registered alpha particles in CR-39 detectors were revealed by employing the conventionally used 6M NaOH/KOH etchant and 5% tetraethyl ammonium bromide (TEAB) as a phase transfer catalyst in 6M NaOH/KOH etchant. Under both compositions of the etchants, CR-39 detectors were etched at 60 °C for 6 h for developing alpha tracks for observations under optical transmission microscope. Alpha track densities (T_d) and alpha track diameters in the etched CR-39 detectors for all samples were measured. The introduction of new chemical etchant effectively improved the uniformity in distribution of alpha tracks, enhanced the track density, and reduced the time of track revelation in CR-39 detectors. Therefore, it could be concluded that the phase transfer catalyst TEAB was highly effective in the etchant for alpha track revelation and detection as compared to conventionally used 6M NaOH etching method. Apart from measuring alpha radio activities, the amounts of ²³⁸U & ²³²Th in the samples were also measured by ICP-MS for understanding the alpha radio activities measured in the coal samples.

Microfabrication of Micropore Array for Cell Separation and Cell Assay

Micropore arrays have attracted a substantial amount of attention due to their strong capability to separate specific cell types, such as rare tumor cells, from a heterogeneous sample and to perform cell assays on a single cell level. Micropore array filtration has been widely used in rare cell type separation because of its potential for a high sample throughput, which is a key parameter for practical clinical applications. However, most of the present micropore arrays suffer from a low throughput, resulting from a low porosity. Therefore, a robust microfabrication process for high-porosity micropore arrays is urgently demanded. This study investigated four microfabrication processes for micropore array preparation in parallel. The results revealed that the Parylene-C molding technique with a silicon micropillar array as the template is the optimized strategy for the robust preparation of a large-area and high-porosity micropore array, along with a high size controllability. The Parylene-C molding technique is compatible with the traditional micromechanical system (MEMS) process and ready for scale-up manufacture. The prepared Parylene-C micropore array is promising for various applications, such as rare tumor cell separation and cell assays in liquid biopsy for cancer precision medicine.

2.5-Dimensional Parylene C micropore array with a large area and a high porosity for high-throughput particle and cell separation

Large-area micropore arrays with a high porosity are in high demand because of their promising potential in liquid biopsy with a large volume of clinical sample. However, a micropore array with a large area and a high porosity faces a serious mechanical strength challenge. The filtration membrane may undergo large deformation at a high filtration throughput, which will decrease its size separation accuracy. In this work, a keyhole-free Parylene molding process has been developed to prepare a large (>20 mm × 20 mm) filtration membrane containing a 2.5-dimensional (2.5D) micropore array with an ultra-high porosity (up to 91.37% with designed pore diameter/space of 100 μm/4 μm). The notation 2.5D indicates that the large area and the relatively small thickness (approximately 10 μm) of the fabricated membranes represent 2D properties, while the large thickness-to-width ratio (10 μm/ < 4 μm) of the spaces between the adjacent pores corresponds to a local 3D feature. The large area and high porosity of the micropore array achieved filtration with a throughput up to 180 mL/min (PBS solution) simply driven by gravity. Meanwhile, the high mechanical strength, benefiting from the 2.5D structure of the micropore array, ensured a negligible pore size variation during the high-throughput filtration, thereby enabling high size resolution separation, which was proven by single-layer and multi-layer filtrations for particle separation. Furthermore, as a preliminary demonstration, the prepared 2.5-dimensional Parylene C micropore array was implemented as an efficient filter for rare cancer cell separation from a large volume, approximately 10 cells in 10 mL PBS and undiluted urine, with high recovery rates of 87 ± 13% and 56 ± 13%, respectively.

Etched tracks and serendipitous dosimetry

Nuclear tracks in detectors that just happened to be there can be found in unexpected places. Eyeglasses, household glass, minerals, objects that were exposed to nuclear explosions, and space equipment on the moon are examples. Such materials allow us to measure doses of past radon exposures, cosmic-ray fluences, fission rates and neutrons. Incidental results include measuring mountain-building rates and deciding where finding oil is likely (or unlikely); in another case erosion rates of surface materials in space are found. New results that assess the effects of hydration layers on the leaching out from glass surfaces of imbedded alpha-recoil nuclei imply that long-term, retrospective radon measurements can be made more reliable by selecting only glass with compact hydration layers.

Fossil Particle Tracks and Uranium Distributions in Minerals of the Vaca Muerta Meteorite

Fossil tracks of charged particles have been observed in minerals separated from the Vaca Muerta mesosiderite. Irradiation of samples of the meteorite with thermal neutrons in a nuclear reactor, together with measurements of track-length distribution, indicate that some of the tracks result from the spontaneous fission of uranium impurities; others, however, are of different origin. Uranium concentrations, which ranged from about 4000 parts per million in a zircon grain to less than 10(-3) parts per million in hypersthene and anorthite, were also measured by irradiating samples with thermal neutrons.