Scintillator solutes

A radiochemical method for the determination of Rn-220 in fumarolic gas is studied. Both condensed water and non-condensing gas are collected together and Pb-212 is precipitated as PbS. After dissolving the precipitate in conc.HCI, it is mixed with an emulsion scintillator solution for activity measurements. As Pb-214 is simultaneously measured, the observed ratio of Pb-212 /Pb-214 gives Rn-220/Rn-222. This method is superior to the method of directly measuring Rn-220 for the samples in which Rn-220/Rn-222 ratios are less than unity. This method and the previously proposed direct method were applied in the field, and new data obtained. An attempt was also made to understand the formation and transport of radon underground. 

Formation and transport of radon ) In the present work, lead isotopes were chemically separated from the sample gas as lead sulfide since the formation of lead sulfide was inevitable under the presence of H2S in the fumarolic gas. The lead sulfide was then dissolved in a small amount of concentrated HCI and mixed with the Insta Gel(emulsion scintillator solution, Insta Gel, Packard Inc.) for the liquid scintillation counting. The chemical yield and the volume of the collected non-condensing gas were obtained from the measurement of the activities of Pb-214 and its progeny which were in radioequilibrium with their precursor Rn-222 whose concentration was determined separately by the direct method. 

This work by Jonah et al. is at variance with the study of Beck and Thomas [400] who did not observe the slower rise of fluorescence intensity when scintillator solutions were radiolytically stimulated rather than photoexcited. Bech and Thomas suggested that the scintillator was excited by excitation transfer from excited state cyclohexane solvent... 

An advanced dioxane-based liquid scintillation solution is developed which incorporated 5 ml. of water and yields a Y value of approximately... 

A Beckman liquid scintillation counting system was used to study scintillation solutions and to analyze environmental samples. All scintillators were obtained from Pilot Chemicals, Boston, Mass. p-Dioxane, spectroscopic grade, and p-xylene (m.p. 12°-13°C.) were received from Matheson, Coleman, and Bell, Rutherford, N. J. 

Chemical quenching occurs when chemical substances in the scintillation solution interact with excited solvent and fluor molecules and decrease the efficiency of the scintillation process. To avoid this type of quenching the sample can be purified or the fluors can be increased in concentration. Modern scintillation counters have computer programs to correct for color and chemical quenching. 

Dilution quenching results when a large volume of liquid radioactive sample is added to the scintillation solution. In most cases, this type of quenching cannot be eliminated, but it can be corrected by one of the techniques discussed below. 

The internal standard ratio method for quench correction is tedious and time-consuming and it destroys the sample, so it is not an ideal method. Scintillation counters are equipped with a standard radiation source inside the instrument but outside the scintillation solution. The radiation source, usually a gamma emitter, is mechanically moved into a position next to the vial containing the sample, and the combined system of standard and sample is counted. Gamma rays from the standard excite solvent molecules in the sample, and the scintillation process occurs as previously described. However, the instrument is adjusted to register only scintillations due to y particle collisions with solvent molecules. This method for quench correction, called the external standard method, is fast and precise. 

Extraction and purification of the sample containing is not required as y-rays penetrate coloured solutions and soft tissue with negligible loss of energy. In the case of p-emitters, the scintillation solution must be colourless or quenching corrections must be applied. 

All radiometric assaying was performed by conventional liquid scintillation counting techniques using a Beckman LS-100 automatic scintillation counter and Ready-Solv GP scintillation solution. 

After washing twice, add 5 mL of scintillation solution to each vial and vortex. 

For the background count, 5 mL of scintillation solution is pipetted into an empty vial. 17a. For the total count, 5 mL of thoroughly mixed (inverted five times) separation... 

Chemical quenching occurs when chemical substances in the scintillation solution interact with excited solvent and fluor molecules and, hence, decrease the... 

Radioactive samples which are insoluble in both toluene and water must be pretreated before analysis. Some insoluble samples can be chemically or physically transformed into a soluble form. A common method is to bum the sample under controlled conditions and collect the 3H20 and/or 14C02 in the scintillation solution. Alternatively, the radioactive substance can be collected on cellulose or fibreglass membrane filters. The filter with the imbedded radioactive sample is placed directly in a scintillation vial containing the proper cocktail. Acidic substances and C02 may be measured after treatment with a base such as hyamine. 

The radioactive sample and scintillation solution are placed in a glass vial for counting. Special glass with a low potassium content must be used because natural potassium contains the radioisotope 40K, a P emitter. Polyethylene vials are also in common use today. 

The high energy y rays are not absorbed by the scintillation solution or vial, but they interact with a crystal fluor, producing scintillations. The scintillations are detected by photomultiplier tubes and electronically counted. 

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