Download e-book for iPad: Charophytes of North America: A Guide to the Species of by R. D. Wood

By R. D. Wood

ISBN-10: 0960389806

ISBN-13: 9780960389803

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Additional info for Charophytes of North America: A Guide to the Species of Charophyta of North America, Central America, and the West Indies

Example text

For example, the ^-disintegration of radiophosphorus leads to the formation of inactive 3 2 S. In other instances, particularly often with natural radionuclides, this is not true. In these cases the immediate decay product is itself radioactive, and a whole chain of radioactive disintegrations may occur. b (uranium series). The other natural decay series are those of thorium and actinium, starting from 2 3 2 Th and 2 3 5 U, respect­ ively. 20. Radioactive Equilibrium After sufficient time, "radioactive equilibrium" (really, a steady state) is established in such decay series.

The effect can be reduced by taking special precautions, such as cooling of the multiplier or use of coincidence circuits. A coincidence circuit consists of two photomultipliers that view the same scintillator and are so connected that registration occurs only when both multipliers produce current pulses simultaneously. This occurs when one and the same light flash in the scintillator is detected by both multipliers. If on the other hand a pulse appears, through spontaneous ejection of an electron, at the output of only one of the two multipliers, it is improbable that a pulse will be produced simultaneously in the second multiplier.

Under certain conditions, the measuring yield may be improved by mixing the active substance with the scintillator. Thus samples containing radiocarbon or tritium, both emitting soft ßradiation, may be brought into a suitable chemical form and then dissolved or suspended in a liquid scintillator. It must be kept in mind that the luminescence of scintillators may be suppressed by foreign substances (quenching). A gas containing radiocarbon or tritium, as is obtained in gas-liquid chromatography (see p.

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Charophytes of North America: A Guide to the Species of Charophyta of North America, Central America, and the West Indies by R. D. Wood


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