14 dating liquid scintillation counter safe single dating

Posted by / 08-Sep-2020 07:41

14 dating liquid scintillation counter

The passive shielding consists of a 650 Kg asymmetric lead block that encloses the sample PMTs.It is constructed from low residual activity lead (from Boliden Mine, Sweden) and the internal cavity surrounding the PMTs is lined with high purity copper (Fig1).These background factors limit the accuracy, precision, and range of the radiocarbon dating method because finite ages can only be calculated where sample activity is at least 3 standard deviations above background activity (Gupta and Polach, 1985).Consequently, each of the components of the LS counting system needs to be totally optimised for low-level counting, so as to maintain high counting efficiency whilst significantly reducing the background.The result is that the smaller of the two time coincident pulses, if also smaller than the set coincidence bias, will not be accepted for pulse summation.

The optimum PAC setting is experimentally determined, and results in lower background levels without significant reduction in counting efficiency.For example, an event originating in one PMT may result in a very large pulse in one tube, and a coincident, small pulse in the other.Events of this nature can be recognised and rejected, by accepting for coincidence summing only those pulses which originate in either PMT, but have an amplitude larger than a certain value, defined as the 'coincidence bias'.We use cookies to make interactions with our website easy and meaningful, to better understand the use of our services, and to tailor advertising.For further information, including about cookie settings, please read our Cookie Policy .

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A layer of cadmium, lined with copper, surrounds the sample PMTs ('S' in Fig 1) to shield against neutrons (Kojola et al., 1984).