CHAPTER 8
158 PerkinElmer Life and Analytical Sciences
chamber and allowed to dark adapt for the specified delay time. Dark
adaption will allow luminescence emanating from the sample vial to dissipate.
Cautions and Limitations
It is important to note that background radiation varies throughout the world, and
will be a factor in determining background. Higher elevations and geological areas
where Uranium and its decay products tend to concentrate will most likely
experience higher background levels. The exact instrument background and
performance for a given location must be determined at the site of the
installation.
Caution:When using the High Sensitivity or Low Level Count
Modes, you MUST NOT use quench standards which have been
purged free of oxygen with an inert gas. The oxygen quenching in
unpurged
standards facilitates discrimination between background
and true beta events. Unpurged standards are available from
PerkinElmer Life and Analytical Sciences. For best DPM
performance, it is recommended that the quench standards match
your unknown samples as closely as possible in terms of cocktail,
vial type and sample volume.
Note: Do NOT
use the Low Level (LL) standards to calibrate (SNC/
IPA) the instrument. It is always calibrated with the unquenched,
purged
14
C calibration standard.
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