Jon Petter Omtvedt & Tor Bjørnstad, Nuclear Chemistry Group
Department of Chemistry, University of Oslo, Norway
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 (see Theory).
d) Record (plot) the scintillation spectra for the two radionuclides.
Reporting Schemes and Results
Table 1: Background Counting
Table 2: Discrimination Settings
Table 3: Determination of the Counting Efficiency of 3H and 14C
On the spectra plots indicate upper and lower limit for CH1 and CH2
Questions for the Students
Here the safety aspects of the exercises should be written. Because of the different rules in different countries this will probably never be correct for every user. It should at least contain HMDS for the chemical compounds used or relevant links to used equipment.
Feedback and improvement ideas from users (student and teachers) for this Laboratory exercise - Liquid Scintillation Counting - is collected here.
Number of counts Sb
Counting time (min)
Counting rate Rb (cpm)
Upper limit (keV)
Lower limit (keV)
Applied Counting Program
Counting rate CH1: RCH1 (background-corrected cpm)
Counting rate CH2: RCH2 (background-corrected cpm)
Disintegration rate standard (dpm)
Counting efficiency CH1: εCH1
Counting efficiency CH2: εCH2
Total counting efficiency in CH1 + CH2: εCH1 + CH2