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At least 289 records · Page 16Linked to original sources
PubMed2003

Increased radon detection sensitivity: extraction from 200 ml of water and liquid scintillation counting.

To increase detection sensitivity in a radon ground-water monitoring program, radon is extracted and transferred from 200 mL of water to a liquid scintillator by bubbling and circulating air through the two liquids in a closed system using a peristaltic pump. This results in a count rate that is 11 times higher than for samples prepared by the most widely used method, where 10 mL of water are added to 10 mL of scintillator. Preparation of counting samples is simple and takes 4 min. Standard deviation in radon concentration is 5% and minimum detectable activity is 5 mBq L(-1), using a counter with a background of 3 counts per hour and a counting time of 3 h. This method is also suitable for the measurement of radium in water.

Equipment Design↗
PubMed1990

A combustion method for the simultaneous determination of 3H, 14C, and 35S in triply labeled organic samples by liquid scintillation counting.

The organic samples triply labeled with 3H, 14C, and 35S were combusted in a flow-type combustion flask under a continuous oxygen flow. The oxygen gas containing the combustion products, which were mainly 3H2O, 14CO2, and 35SO2, was introduced into successive 0.5 M H2O2 and Oxisorb (2-methoxyethylamine). The 35SO2 and 3H2O that had been partially adsorbed onto the inner wall of the combustion flask were recovered by rinsing the wall with an H2O2 solution. 3H and 35S were quantitatively recovered from the H2O2 solutions. 14C was not found in the H2O2 solutions and was recovered from Oxisorb quantitatively. The amounts of 3H, 35S, and 14C were determined by measuring the radioactivity of the H2O2 solutions and of Oxisorb with a liquid scintillation counter. Thus the separate determination of 14C and 35S in a sample was achieved. Through this combustion method, the materials including fresh animal tissues up to ca. 300 mg were conveniently combusted with quantitative recovery of 3H, 14C, and 35S.

Carbon Dioxide↗
PubMed1987

Utilization of hydroxyurea for detection of DNA repair synthesis in liver following dimethylnitrosamine action by means of scintillation counting.

We detected DNA repair synthesis by employing hydroxyurea as an inhibitor of DNA semiconservative synthesis in various time schedules of experiments. We came to the conclusion that prolongation of the time interval between [3H]thymidine administration and sacrifice of the animals from 0.5 h to 7.5 h increases the sensitivity of examination. Some artifacts associated with detection of the repair (hydroxyurea-resistant) synthesis of DNA are discussed.

Animals↗
PubMed1987

Lymphocyte proliferation and cytotoxic assays using flat-bed scintillation counting.

Lymphocyte 51Cr release and [3H]thymidine uptake assays were evaluated with respect to measurement of sample radioactivity using the flat-bed scintillation counter. 51Cr lysates were spotted onto a glass fibre filter sheet while [3H]thymidine-labelled cells were filtered onto a similar sheet using a cell harvester. The 96 samples were rapidly processed for counting, without removal of individual sample areas. Either form of preparation showed good linearity of count rate with the quantity of material on the filter. Reproducibility was good; the coefficient of variation for 96 samples being within 5%. The low background and high efficiency of this counter results in increased assay sensitivity and allows considerable economies in materials to be made. A commercial version of the counter has six counting heads permitting a high rate of sample throughput.

Beta Particles↗
PubMedDate not supplied

Development of 3-PM liquid scintillation counting system with geometrical efficiency variation.

An improved triple-to-double coincidence ratio system has been developed to obtain efficiency variation by means of geometrical displacement, that is, three photomultiplier (PM) tubes move back and forth direction from a vial source. The detection unit of the system is located in a cylindrical chamber for light shielding, and a stepping motor connected to the three PM tubes controls the source-to-detector distance up to 50 mm with 1 mm resolution. In activity measurements of 14C and 204Tl using this measurement technique, the efficiencies varied from 0.60 to 0.90 for 14C and from 0.87 to 0.96 for 204Tl. In this study, the characteristics of the system are described as well as data acquisition and analysis methods.

Algorithms↗
PubMed1993

Quantification of specific mRNA by flatbed scintillation counting of dual-labeled dot blots.

A dual-labeling technique was developed for direct quantification of specific mRNA using a flatbed liquid scintillation counter. This method simultaneously measures cpm of 32P- and 35S-labeled probes bound to RNA dot blots and subtracts counts due to nonspecific background radioactivity bound to the filter. Probes for T-cell receptor and beta-actin (as the internal standard) were hybridized both separately and simultaneously to RNA isolated from five different sources. There was concordance between the radioactivity measured from single- and dual-hybridizations for each combination of 35S- and 32P-labeled probes. This methodology directly quantifies specific mRNA sequences bound to membranes and has potential for measuring gene dosage, without the need for re-probing or densitometric analysis.

Actins↗
PubMed1984

[Optimization of liquid scintillation counting by using multichannel pulse-height analyzer].

The method for determining optimum conditions of a liquid scintillation counter (LSC) for low-level counting of tritium was studied. To compare the lower limit of detection, the figure of merit EM/square root B was used. Th measurement system is a LSC connected with a multichannel pulse-height analyzer (MCA). Both of tritium spectra and background spectra were searched for the condition that maximizes the figure of merit. The optimum condition obtained by using the MCA was fitted for a single channel pulse-height analyzer of the LSC. The figure of merit obtained by this method was 20.6% greater than that obtained by the balance point method.

Arginine↗
PubMedDate not supplied

Standardization of tritiated water and 204Tl by TDCR liquid scintillation counting.

The triple to double coincidence ratio method was used with a combined uncertainty of 1-2% to standardize tritiated water and a solution of 204Tl. The vial with liquid scintillator, in which the sample to be measured was dissolved, is optically coupled to three photomultipliers. The electronic module MAC-3 assures the selection of double and triple coincidences count rates, D and T, from the three counting channels. It contains the gating circuits, necessary to obtain the livetime value and the extended deadtime circuit. Specific computer programs were used to calculate the free parameter value, the efficiency of D and so, the value of the activity. The optimal value of the Birks ionisation-quenching parameter, kB, was evaluated by changing the detection efficiency with grey filters. Three types of liquid scintillators, namely InstaGel, PPO+POPOP+Triton in toluene and Ultima Gold, were employed. 204Tl was measured in the frame of an international comparison organized by BIPM. For tritiated water a comparison was made with LNHB-Saclay; the relative difference between the obtained values for the massic activity was only 0.2%.

Algorithms↗
PubMed2001

Simultaneous measurement of 89Sr and 90Sr in aqueous samples by liquid scintillation counting using the spectrum unfolding method.

Two radiostrontium isotopes, 89Sr and 90Sr, were measured simultaneously by liquid scintillation counter coupling with a full spectrum DPM counting protocol. Strontium was separated from the aqueous media by extraction chromatography using Sr-spec resin. Individual count rates were evaluated from quench correlation curves for 89Sr and 90Sr related with SIS and tSIE quench indicators. The method exhibited a counting efficiency of 95% for 89Sr and 92% for 90Sr within their full energy channels and gave highly precise results when the sample was counted within 4 h after strontium separation. Lower limits of detection were 37 mBq/l for 90Sr and 32 mBq/l for 89Sr with a 60 min counting time.

Journal Article↗