New dosimetry methods for radiological and nuclear emergency management

Alghamdi, Hamdan Mahmal Saad (2025) New dosimetry methods for radiological and nuclear emergency management. PhD thesis, University of Glasgow.

Abstract

During all phases following a nuclear or radiological incident analyses of doses received by members of the public and responders are required. Rapid and reliable dose assessment is critical for the effective management of radiological emergencies; for medical triage, understanding exposure levels, directing protective actions, and conducting subsequent analyses of the impact of the incident. Current practice has been reviewed, highlighting the potential for near real-time luminescence dosimetry to assist with such assessments, including low dose response that supports public reassurance below doses of medical significance, using common materials present at the time of the incident. A number of materials which might be found in the immediate vicinity of people have previously been investigated with regard to their potential to act as radiation dosimeters. The work in this thesis investigates the properties of common household salt and talc, using portable Optically Stimulated Luminescence (OSL) and Infra-Red Stimulated Luminescence (IRSL) instruments capable of rapid measurements in the field. The potential of these materials to measure radiation levels and provide rapid, cost-effective insights into exposure patterns using new methods is explored. This approach aims to support emergency response strategies by leveraging accessible materials to improve decision-making in radiological incidents, bridging a key gap in large-scale radiation measurements and initial triage support.

Common salt has previously been shown to have the potential for retrospective dosimetry in the mGy dose range using laboratory instrumentation. This thesis investigates the use of portable instruments, with unprepared commercially sourced salt, in dose ranges below mGy. Responses from pulsed IRSL laboratory systems and portable OSL instruments were compared. For OSL measurements, detection limits of 7µGy have been demonstrated, with detection limits of 30-340µGy for the other instruments investigated. Linear dose responses in the 0-500µGy range were determined over this dose range. This work examines the effects of signal stability and sample storage conditions. The OSL signals initially show a brief decrease in luminescence during the first few days after irradiation, followed by a gradual increase with longer storage periods. Between days 8 and 64, the results remain relatively stable, which is crucial for dose estimation during both the early and later stages of responding to radiological emergencies, and methods for correcting for these signal variations at shorter and longer periods have been developed and demonstrated. However, exposure to light and moisture leads to a rapid loss of OSL signals.

Three practical experiments were conducted using salt to simulate real accident scenarios, measure radiation, estimate dose, and compare the results with gamma systems (backpack). The first experiment was conducted under controlled laboratory conditions. The second mapped natural and artificial radiation fields in an outside environment. The final experiment mapped complex radiation fields within an accelerator laboratory. The results demonstrate that salt has considerable potential for use in dosimetry below mGy and that measurements can be conducted with portable OSL instruments. Furthermore, the results of the first two experiments compared well to theoretical doses and measurements with different systems. The results confirmed that this approach can provide reliable dose estimates for radiological accidents. The salt system has demonstrated its ability to map the spatial boundaries of radiation fields, serving as a low cost radiation mapping tool. Protocols must be instituted for testing and assessment during exercises, taking into account variables such as zeroing, ambient conditions, and the necessity for fading adjustments.

The studies of talc focused on the optimal conditions for measuring the radiation-induced OSLsignal using the SUERC Portable OSL Reader. It also addressed the inherent complexities associated with geological residual signals observed in talc sourced from Luzenac Pharma's packing line. This residual signal can be removed through thermal treatment, specifically at 400°C for 1 hour, after which the talc exhibits sufficient sensitivity to detect doses in the mGy range through to the radiologically significant range of 0.5 to 3 Gy, making it a promising candidate for field-deployable radiation assessment, such as in emergency response scenarios following radiological incidents. However, the observed fading and zeroing behaviours of talc introduce critical considerations that must be addressed to ensure reliable dose estimation. The fading data exhibit a complex decay pattern, suggesting the presence of multiple trap depths, with an initial signal loss of approximately 6% within 24 hours post-irradiation, escalating toa substantial 65% reduction of the original OSL signal within 128 days at ambient temperature. Such behaviour necessitates the incorporation of fading correction factors tailored to the time elapsed between irradiation and measurement, as an uncorrected signal loss could lead to systematic underestimation of doses, particularly in retrospective dosimetry applications. Additionally, the zeroing behaviour poses further challenges. Incomplete zeroing could leave residual signals that overlap with those induced by a recent radiation event. This overlap complicates the ability to accurately distinguish between background dose contributions and acute doses from a specific incident, potentially compromising the method’s specificity.

The work presented here has demonstrated that the novel approach of using salt or talc with portable OSL systems is capable of delivering dose estimates in the range from a few µGy to several Gy in near real-time, complementing existing techniques. To optimize this approach, comprehensive protocols should be developed for both testing exercises and evaluations, which could lead to wider acceptance of these approaches offering a robust, low-cost solution for rapid dose assessment for both emergency response and environmental dosimetry.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: The work was conducted at SUERC within the PhD programme of H. M. S. Alghamdi, supported by a scholarship from the Government of the Kingdom of Saudi Arabia.
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Funder's Name: Government of the Kingdom of Saudi Arabia
• Supervisor's Name: Sanderson, Professor David and Cresswell, Dr. Alan
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85442
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 10 Sep 2025 08:53
• Last Modified: 10 Sep 2025 08:55
• Thesis DOI: 10.5525/gla.thesis.85442
• URI: https://theses.gla.ac.uk/id/eprint/85442

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