PubMed · 5251834
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S Jeretin, M Hribar, Z Milavc. 1966. A new control and trigger unit for ventilators.. https://doi.org/10.1111/j.1399-6576.1966.tb01112.x
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Alpha particles have been measured coming from the surfaces of rocks covered with dark red-brown rock varnish, as well as rocks that appear to have little, if any, varnish. A pronounced peak at 5.3 MeV indicates the presence of 210Po, a short-lived natural-radioactive element. Surface activities for 33 samples range from 0.008 Bq/cm2 to 0.065 Bq/cm2. It is estimated that this nuclide is concentrated 10(11) times in these paper-thin coatings above its concentration in ground-level air. Gamma rays from the decay of 137Cs, a product of testing nuclear weapons some 50 years ago, were also detected. Analysis of samples of varnish stripped from the rock revealed traces of 239,240Pu and 238Pu. The presence of all of these isotopes strongly supports the theory that varnish films derive their building blocks from the atmosphere and, with time, all rocks in arid environments will become coated.
The autoradiographic micromapping of rocks with various U and Th contents has been performed by means of CR-39 solid-state nuclear track detector (SSNTD). The optical track density was found to be highly correlated (r=0.92) with total alpha emitters activity calculated on the basis of field gamma spectrometric measurements of rock outcrops. The method was tested not only for the wide range activities of alpha emitters but various types of surface distribution (including highly radioactive mineral grains) as well.
Bystander effects from ionizing radiation have been detailed for a number of cell systems and a number of end points. We wished to use a cell culture/ex vivo rat model of respiratory tissue to determine whether a bystander effect detected in culture could also be shown in a tissue. Examination by immunofluorescence techniques of tracheal cell cultures after exposure to very low doses of alpha particles revealed a large proportion of cells with proliferating cell nuclear antigen (PCNA) bound in their nuclei. PCNA was selected as an end point because it is involved in both DNA repair and the changes in cell cycle that are typical of many reported bystander effects. Maximum response can be detected in up to 28% of the cells in sub-confluent cultures with a dose of only 2 mGy. At this dose less than 2% of the cell nuclei have experienced a particle traversal and less than 6% of the cells have experienced an alpha-particle traversal through either their nucleus or some part of their cytoplasm. The hypothesis that this bystander response in nontargeted cells is mediated through secreted factor(s) is presented, and supporting evidence was found using partial irradiation and co-culture experiments. Examination of the effect with excised pieces of trachea demonstrated a response similar to that seen in culture.