OPTIMIZATION OF LSC AND COMBUSTION PROTOCOLS FOR OBT MEASUREMENTS OF WHEAT AND SEAWEED MATRICES

Abstract

This project involved the testing and establishment of a base combustion procedure for the newly acquired Raddec Gen IV PYROLYSER and focused on the optimization and correction of the laboratory’s previous liquid scintillation counting (LSC) procedure using the Hidex 300 SL.

The pyrolyser was verified to be operational and achieve satisfactory and consistent recoveries across the 6 combustion tubes. A custom organic combustion template was created to process masses of 8 g to 19 g of seaweed (Fucus serratus and Fucus vesiculosus) and wheat-like samples. Recovery rates of (85±8) % to (100±10) % and (88±1) % to (94±1) % were achieved for seaweed and wheat, respectively. The combustion water yield was increased by 2 to 4 times compared to that of the default organic combustion template from the manufacturer. Furthermore, a post- combustion sample cleaning procedure was introduced and assessed in order to lower the quench of the combustion water.

Technical corrections to the Hidex 300 SL included refinements to the Triple-to-Double Coincidence Ratio (TDCR) calculations and the rectification of the uncertainty estimation logic. Experimental validation confirmed that the manufacturer’s default coincidence time of 35 ns is the optimal value for this system. The optimized Region of Interest (ROI) was determined to be channel numbers 20 to 195. A well-characterized background model was developed, resulting in a 25 % decrease in the Minimum Detectable Activity (MDA) for relevant samples. Additionally, accounting for the covariance between double and triple coincidences resulted in a (21 ± 2) % decrease in the activity uncertainty.

To automate data quality control, a custom data cleaning pipeline was introduced utilizing quartile filtering, z-score progression, and a custom signs test to identify outliers. This methodology resulted in the rejection of 5.1 % of measurement repetitions and a mean activity reduction of (34 ± 27) %, for affected samples. These functionalities were integrated into a custom-built Py- Side 6 application, providing post-measurement parameter alteration, custom outlier selection, and interactive visualization of the cleaning process.

Popular Abstract

Organically bound tritium (OBT) can be found in every person, animal, and plant on Earth. It might be unsettling to think that a radioactive form of hydrogen has somehow woven itself into your very biological makeup, but the process is a simple consequence of the world we live in. However, there is no need for alarm. Tritium is created naturally when energetic particles from the sun slam into our upper atmosphere. These natural levels are typically 5000 to 10 000 times below the safety limits set by the World Health Organization. Ultimately, as with any substance, the dose makes the poison. Tritium is a radioactive form of hydrogen that is 3 times heavier. It is most commonly stored in water known as HTO where a standard hydrogen atom is swapped for its radioactive cousin. Because this “heavy” water participates in the global water cycle, tritium is an incredibly mobile traveler, spreading easily into the food we eat, the water we drink, and even the air we breathe. Human activities provide a further source of tritium, with Cold War nuclear weapons testing being the most extreme case. The International Atomic Energy Agency estimates that 520 kg to 660 kg of tritium was released over a 28-year period, roughly 70 times more than what nature produced in that time period. To visualize that gap, it is the difference in height between a modest apartment building and a modern skyscraper. While the effects of this period are still detectable, environmental levels have now returned to levels close to the pre-weapons-testing era. This history of nuclear weapons testing originally motivated scientists to track tritium in HTO to determine the radiation dose experienced by the public. Recently, however, researchers have shifted their focus toward OBT. This is tritium that is stored in our tissues. OBT spends much more time in the body than HTO. This is intuitive: the water in our bodies is replaced rapidly while the biological tissues are produces slowly. Consequently, if the same amount of OBT and HTO were introduced into your body, the body receives 2–3 times more radiation from OBT because it lingers so much longer. Tracking both HTO and OBT in the surrounding environment of modern facilities that produce tritium is a growing field, particularly around nuclear power plants, fuel reprocessing centers, and research facilities. These facilities release tritium into the local air and water according to strict regulations, and monitoring tritium in the environment allows us to verify that these rules are being followed. Lund University is currently expanding its monitoring to include OBT, specifically to track levels around plants like Ringhals and Barseb¨ack, as well as the effects of the European Spallation Source on the local environment. Measuring the OBT found in plants involves two main steps: removing the tritium from the plant and then measuring it. My project focuses on creating a routine to get the best possible results 1 from these two steps. The samples are burnt in the furnace and released as water molecules we can collect. Tritium does not get released at the same rate as its cousin hydrogen, due to being 3 times heavier. Accurate measurements therefore require all the tritium and hydrogen to be freed. If this is not done the measurement under or over reports the amount of tritium. Part of my project is to create a protocol to facilitate this ’complete combustion’. Often, environmental samples contain such tiny quantities of tritium that they push our equipment to its absolute detection limits. If this were a high jump, the “bar” would be the detection limit and the height of the “jump” would be the quantity of tritium. If you cannot clear the bar, the height of your jump cannot be measured. The other part of my project focuses on finding the best measurement conditions to “lower the bar,” allowing us to capture more data. With the overall goal of providing consistent and accurate determinations for the amount of tritium for as low of tritium quantities as possible.
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• author: Mc Caughley, Sean Francis Donnell
• supervisor: Guillaume Pedehontaa-Hiaa; Charlotta Nilsson; Kristina Stenström
• organization: Department of Physics; Particle and nuclear physics
• course: FYSM64 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: Tritium, OBT, LSC, Combustion
• language: English
• id: 9231321
• date added to LUP: 2026-06-17 13:47:02
• date last changed: 2026-06-17 13:47:02