KJM5911 Lab Exercise 5 - Liquid Scintillation Counting

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Learning Goals

  • Understand the theory behind Liquid Scintillation detection.
  • Understand how the detection equipment in Liquid Scintillation works.


Experimental procedure

We are going to use a modern liquid-scintillation counter (LSC) with three PM-tubes. This enables it to use the Triple-to-Doubble-Coincidence-Ratio (TDCR) parameter for quench correction. We will both use the traditional channel-ratio method and the TDCR method to investigate quenching in LSC samples. For this we will use 14C samples quenched with CCl.

Part 1: Initial tests

  • Measure 3T and 14C standards to get familiar with the machine (HIDEX 300) (2 min each).
  • Measure an empty vial with 10-mL scintillator (and nothing else) inside (10 min or more).
  • Measure an empty vial without scintillator solution (10 min or more).

Part 2: Quench Correction

  • Prepare 10 20-mL vials with 10-mL LSC cocktail in each
  • Add a suitable amount of 14C activity to obtain at least 50,000 counts in a 2- or 3-min measurement.
  • Measure the 10 samples to check for consistency - they should all give the same result.
  • Quench 9 of the samples with suitable amounts of CCl (10-200 uL) to cover the whole quenching range.
  • The measurement results will contain Doubble-Coincicdence and Triple-Coincidence spectra. There is also predefined regions of interest (ROI) which can be used to calculate the traditional quenching parameter (channel ratio) directly (instead of integrating different parts of the spectra).

Part 3: Mixture of 3H and 14C

  • Prepare one sample with only 3H and one sample with about equal amounts of 3H and 14C.
  • Count the samples (count until you have at least 50,000 counts in each).
  • Compare the 3H spectrum to the 14C spectrum from Part 1 (or 2). How can such mixtures be analysed to get the desintegration rate of the individual nuclei?
  • Get an unknown sample from your supervisor and count it. The 3H and 14C content of this sample should be determined.

Part 4: Other nuclei

  • A solution of H3PO4 has been n-irradiated for several days.
  • Prepare two samples: Extract 200 uL from the H3PO4 solution and add it to A) a counting vial with 10 mL scintillation cocktail and B) a counting vial with 10 mL deionised water.
  • Count both solutions with suitable setups (your supervisor will guide you).


  • HIDEX 300 Automatic TDCR Liquid Scintillation Counter

Safety Aspects