Biomedical subjects

P Theodorsson

Publications and source records attributed to P Theodorsson.

4 recordsLinked 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↗

PubMed2000

A multi-sample liquid scintillation counting system for weak beta-emitting samples with single phototube detectors

The relative merits of low-level liquid scintillation counters with one and two phototubes, respectively, are discussed and an analysis of their background components is presented. A simple and compact system with manual sample changing is described. It counts four samples simultaneously, and it is based on the single-phototube arrangement where conical vials sit on the top of 28 mm diameter phototubes. A PC computer collects and processes the pulses from a specially designed electronic unit. The system is operated in a small underground counting room, a closet in the wall of a road tunnel under a fjord. Its performance is described.

Journal Article↗

PubMed2000

A compact automatic low-level liquid scintillation system for radon-in water measurement by pulse pair counting

A novel compact liquid scintillation counting system with automatic changing of seven samples, dedicated to the assay of low levels of 222Rn in water, is described. Its has a single phototube, and its operating mode is 222Rn series selective, as only the close pulse pairs given by 214Bi and its short lived decay product 214Po (half life 0.16 ms), are counted. Its 214Bi/214Po counting efficiency is 90.4% and the background, with an unshielded detector, is 3 pulse pairs per hour. 75% of the radon in 200 ml water samples is transferred to the scintillator (15 ml toluene) by circulating air, which is bubbled through the two liquids for 4 min. With a counting time of 3 h, the minimum detection level is 8 mBq l(-1). The method is also suitable for various environmental and geophysical studies of 222Rn and 226Ra.

Journal Article↗

PubMed1999

A review of low-level tritium systems and sensitivity requirements.

Data from three international intercomparison projects are used to study the state of the tritium low-level technique and to set a realistic sensitivity level that should be demanded in ultralow-level tritium work, mainly in hydrology and oceanography. Only two laboratories reach the required goal, a standard deviation < or = 0.03 TU for weak samples. The methods used are described and important parameters illustrated graphically. Possible improvements in the measuring techniques are discussed, including the design of better counting systems.

Electrolysis↗