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At least 163 records · Page 9Linked to original sources
PubMed1979

Measuring radioactive methane with the liquid scintillation counter.

Although a gas proportional counter is the most convenient method of measuring the radioactivity of fixed gases such as methane, it cannot be used when high nonradioactive concentrations of methane are present in the gas phase, due to quenching. If only methane and carbon dioxide are present in radioactive form in the gas phase, a liquid scintillation method for measuring these substances can be used. The procedure is described in detail, and the solubility of methane in liquid scintillation cocktails is determined.

Journal Article↗
PubMed1990

The use of caesium iodide mini scintillation counters for dual isotope pulmonary capillary permeability studies.

A commercially available system of caesium iodide crystal mini-detectors (Oakfield Instruments, Oxon, UK) was modified so that it was suitable for dual isotopic measurement of the plasma protein accumulation index (PPA)- a measure of pulmonary endothelial permeability. Using this modified system the mean PPA x 10(-3) min-1 +/- (S.E.M.) recorded in 11 normal subjects (22 lungs) was 0.18 (0.08) and in 6 patients (9 lungs) with the adult respiratory distress syndrome was 2.88 (0.63) (P less than 0.02). These values for PPA concur with those found by other groups using larger sodium iodide detectors. We conclude that with simple modification caesium iodide mini-detectors may be used successfully for the measurement of PPA in the intensive care setting.

Capillary Permeability↗
PubMed1979

[Evaluation of the reproducibility in radioactivity measurements with liquid scintillation counters--effect of anomalous count rate-dependent photomultiplier gain variations (author's transl)].

Time variations in count rate were measured for prolonged period of time using a set of 3H samples and a few other specially prepared samples of 14C, 32P, and 137Cs. Besides, beta-ray spectra of a particular 3H sample were measured as a function of time with a multichannel pulse height analyzer. These measurements lead to the following conclusions: (1) Anomalous count rate variations are attributed to strong dependence of photomultiplier gain on count rate. (2) Different steady state count rates can be observed for 3H samples having activities of approximately 10(5) dps when they are measured immediately after the measurements of background and 3H samples of higher activities. (3) The count rate-dependent effect on photomultiplier gain can be described properly by the current flowing through the tube rather than the count rate. (4) The measurement of the external standard channel ratio using the built-in 137Cs source can affect seriously the successive measurements on 3H samples, while the channels ratio itself exhibits strong time dependence.

Evaluation Studies as Topic↗