PG-RAD: A Tool for Simulating Radiometric Data for Mobile Radioactive Source Searches and In Situ Measurements

Abstract

The loss of regulatory control over radioactive material and sources poses great risks to public safety. Such a situation necessitates the development of protocols and methods for effective and accurate localisation, characterisation and securement of the materials. Mobile gamma spectrometry, particularly using vehicle-borne detectors, has emerged as a viable method for in-situ characterisation of the gamma radiation field, and has been successfully used in searches for locating lost gamma sources. Traditional localisation methods rely on the peak count rate and full width at half maximum of the characteristic count rate curve as a vehicle-borne detector passes a source. However, assumptions required for these methods often fail due to real-world complexities. Bayesian search methods have been developed as a robust alternative, but further validation is needed to test its effectiveness and find the limiting cases.

This thesis presents PG-RAD (Primary Gamma RADiation simulator), a modular toolbox for simulating mobile search scenarios of gamma sources. PG-RAD generates synthetic counts that would be observed by a detector travelling along a path as it passes a gamma source. PG-RAD accounts for angular detector efficiency, air attenuation and counting statistics. PG-RAD is flexible in the definition of point sources and trajectory geometry. To demonstrate its applicability to research in source localisation methods, simulations of both HPGe and NaI(Tl) detectors were performed, simulating mobile search of Caesium-137 sources. PG-RAD was validated against existing reference codes and experimental data. It was also used to systematically test a two-source Bayesian localisation algorithm, assessing its performance as a function of source separation and difference in activity.

Results show that PG-RAD is able to generate representative count data, and can effectively be used for testing mobile search algorithms. The lack of shielding and Compton scattered photons likely account for the discrepancies found when comparing to some experimental data. However, because PG-RAD is developed as an open source toolbox, taking a modular and object-oriented approach, future implementation of these features is possible to enhance the realism of the generated data. Furthermore, other detectors or isotopes could be added in order to make PG-RAD useful for other research teams around the world.

Popular Abstract

There are many use cases for radioactive materials in the modern world, such as medical care, nuclear power and industrial applications. However, radioactive sources can be very dangerous when handled incorrectly. That is why there are strong regulations all around the world to handle radioactive material securely. Despite that, radioactive material sometimes gets stolen or simply lost. It happens more than one may think: in 2025 alone, the International Atomic Energy Agency received more than 200 reports of stolen radioactive material. When a radioactive source is lost out of the regulators’ control, effective localization of the material is very important to avoid harm to people. One method that has proven effective for searching for radioactive sources is mobile gamma spectrometry. By putting detectors on a vehicle such as a car, plane or drone, a much larger area can be searched than is possible with handheld detectors.

The objective of this thesis work is to develop a simulator program which can generate data that mimics mobile search scenarios of radioactive sources. Such a simulator is useful, because it allows researchers to test many different scenarios relatively quickly and cheaply. The program developed in this thesis is called PG-RAD. A few different scenarios were generated and compared to real-world data. To showcase the potential future uses, PG-RAD was also used to simulate how a drone might detect a radiation source from above. Finally, PG-RAD was used to test Bayesian methods in mobile search of radioactive material. Bayesian statistics is an advanced kind of statistics, and recent studies show it could be useful in mobile search scenarios. PG-RAD was able to generate lots of different scenarios very quickly, and pass this data to the Bayesian algorithm with success.

In conclusion, PG-RAD is useful for simulations of mobile search scenarios. The fact that it is a modular program means adding new modules or improving old ones is straightforward. Future work could include making the simulations more realistic by improving the physics models, and allowing for objects to be placed in the world that affect the detection of a radiation source, such as vegetation and buildings.

Popular Abstract (Swedish)

Radioaktiva ämnen har många användningsområden i sjukvård, forskning, industri och kärnkraft. De kan dock vara farliga om materialet hanteras på fel sätt. Därför finns stark reglering av användningen över hela världen. Trots detta kommer radioaktiva ämnen ibland bort, på grund av stöld eller felaktig hantering. Radioaktivt material kommer bort oftare än vad man kanske tror. Internationella atomenergiorganet (International Atomic Energy Agency) tog år 2025 emot fler än 200 anmälningar om stulna radioaktiva ämnen. I sådan fall är det viktigt att snabbt lokalisera materialet, så att man kan undvika att människor kommer till skada. En användbar metod för att lokalisera förlorade radioaktiva källor är mobil sökning. Genom att montera strålningsdetektorer på ett fordon, till exempel en bil, en helikopter eller en drönare, kan man mäta gammastrålning från radioaktiva ämnen över ett mycket stort område och snabbt söka efter strålkällor.

Syftet med detta examensarbete är att simulera scenarier för mobil sökning av radioaktiva källor. En sådan simulator är användbar eftersom forskare kan testa många olika scenarier med den, relativt snabbt och kostnadseffektivt. Simulatorn som utvecklats i examensarbetet kallas PG-RAD. I arbetet genererades ett antal olika scenarier som jämfördes med data från verkliga händelser. För att visa på möjliga framtida användningsområden användes PG-RAD även för att simulera hur en drönare skulle kunna upptäcka en gammastrålkälla från luften. Slutligen användes PG-RAD för att testa bayesianska metoder vid mobil sökning efter radioak-
tivt material. Bayesiansk statistik är en avancerad typ av statistik, och nya studier visar att den kan vara användbar i scenarier med mobil sökning. PG-RAD kan mycket snabbt generera många olika scenarier och framgångsrikt överföra dessa data till den bayesianska algoritmen.

Sammantaget är PG-RAD ett användbart verktyg för simuleringar av mobil sökning efter gammastrålkällor. Eftersom simulatorn är modulär är det enkelt att lägga till nya moduler eller förbättra befintliga. Framtida arbete skulle kunna inriktas på att göra simuleringarna mer realistiska genom att förbättra fysikmodellerna, som beskriver hur objekt i miljön påverkar uppfattarstrålningens spridning och absorption, till exempel i träd och byggnader.

• author: Nelissen, Pim
• supervisor: Christopher Rääf; Crister Ceberg; Aliaksandr Dvornik; Robert Finck
• organization: Mathematics (Faculty of Sciences); Centre for Mathematical Sciences
• course: BERM03 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy; Mathematics and Statistics
• keywords: Mobile gamma spectrometry, Gamma source localisation, Vehicle-borne detection, Bayesian, Ionizing radiation, Radiation field characterisation, Nuclear security, Emergency preparedness
• publication/series: Master’s Theses in Mathematical Sciences
• report number: LUNFBV-3017-2026
• ISSN: 1404-6342
• other publication id: 2026:E75
• language: English
• id: 9238749
• date added to LUP: 2026-07-27 10:51:39
• date last changed: 2026-07-27 10:51:39