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The students are first divided into two groups. Each group follow the procedures described below.

Laboratory Procedure

Determination of the counting efficiency of 3H and 14C
a) Prepare one standard sample (unquenched) for each of the two radionuclides 3H and 14C in two separate liquid scintillation vials. This is done by extracting an aliquote of 1.00 mL from the respective mother solution into the two vials. Add 10 mL scintillation cocktail to each vial and shake to a homogeneous solution.
b) Count the standard samples on the Beckman LS counter in the MCA mode. Define channel 1 as the counting window covering the 3H spectrum, and channel 2 as that part of the 14C spectrum which does not overlap with the 3H spectrum. For 14C record the counting rate in both channels.
c) Determine the counting efficiency εCH1(3H), εcH1 (14C), εCH2(14C) and εCH1 + CH2(14C) from eqn 2 in Interfering Processes
d) Record (plot) the scintillation spectra for the two radionuclides.

Reporting Schemes and results

Suggested appearance
Table 1: Background Counting
Number of counts Sb

Counting time (min)

counting rate Rb (cpm)

Table 2 Discriminator Settings

Upper limit (keV)

Lower limit (keV)

Table 3: Determination of the Counting Efficiency of 3H and 14C
Applied Counting Program

Counting rate CH1: RCH1
(background-corrected cpm)

Counting rate CH2: RCH2
(background-corrected cpm)

Disintegration rate standard

Counting efficiency CH1: εCH1

Counting efficiency CH2: εCH2

Total counting efficiency in CH1+CH2: εCH1 + CH2

On the spectra plots indicate upper and lower limit for CH1 and CH2.