The modelling and measurement of nuclear reaction cross-sections & the production of a technetium fission yield tracer

Allen, Ross A.M. (2023). The modelling and measurement of nuclear reaction cross-sections & the production of a technetium fission yield tracer. University of Birmingham. Ph.D.

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Abstract

The 20\(^{th}\) century saw the dawn of the nuclear age, in which humanity harnessed the strong nuclear force through the nuclear processes of fission and fusion. Nuclear science expanded our understanding of matter beyond chemical elements, to include over 7,000 predicted nuclei, each with discrete characteristics born out of their nuclear structure. An understanding of nuclear reactions and decay of nuclei enabled energy production with densities orders of magnitude greater than traditional means, and the diagnosis and treatment of a range of diseases. These advancements also came with baggage in the form of security and environmental challenges. The characterisation and detection of radionuclides is of huge importance in nuclear science, whether that be optimising the operation of nuclear reactors based on the distribution of fuel products, the detection of clandestine nuclear activity by rogue states through the detection of products produced in nuclear weapons testing, and the mitigation of environmental damage by accurately being able to quantify the transport of radionuclides through matter and the biosphere. All isotopes of a given element act chemically identically due to their identical electron configuration, however, they each possess unique physical fingerprints in the form of decay channels, reaction probabilities, and reaction mechanisms. The combination of these factors opens up a realm of possibilities, whereby the chemical transport of different isotopes of the same element is identical, while the presence of different isotopes can be determined by their unique nuclear characteristics, two facts which are leveraged with radiotracers. The field of radiotracers is ubiquitous in medicine, energy, and nuclear security, with the production of high-purity radioactive isotopes with specific physical and chemical characteristics for a range of applications in an evolving field.

The development of such a tracer involves several stages, centering around the optimisation of nuclear reactions to enable the production of exotic elements and isotopes often not present in nature, which through optimised particle accelerator production combined with a series of refined chemical separation steps can produce high isotopic purities. This thesis focuses on developing a radio-tracer of \(^{97}\)Tc for the analysis of long-lived fission product \(^{99}\)Tc. The workflow can act as an effective template for future tracer development, with clear steps from concept to a standardised tracer suitable for commercial deployment. With \(^{99}\)Tc being a high-yield fission product produced 6.1% of the time in thermal neutron-induced fission of \(^{235}\)U [1], a commercially viable mass tracer for technetium-99 is highly sought after in the nuclear industry, with applications in nuclear security, decommissioning, environmental monitoring and optimising reactor power cycles.

As a mass spectrometry tracer of \(^{99}\)Tc, \(^{97}\)Tc was determined as the only suitable candidate isotope, produced indirectly through the decay of a \(^{97}\)Ru generator. Six reactions were then compared using natural abundance targets: \(^{nat}\)Mo(\(^{3}\)He,xn)\(^{97}\)Ru, \(^{nat}\)Mo(α,xn)\(^{97}\)Ru, \(^{nat}\)Ru(p, X)\(^{97}\)Ru, \(^{nat}\)Ru(d, X)\(^{97}\)Ru, \(^{nat}\)Ru(\(^{3}\)He,X)\(^{97}\)Ru, and \(^{nat}\)Ru(α,X)\(^{97}\)Ru. A computational tool for the running of nuclear reaction modelling and isotope inventory calculations called ”The University of Birmingham Tool for Isotope Production (UoB-TIP)” was developed during this project. This software enabled a range of nuclear reactions to be modelled using TALYS and TASMAN nuclear reaction codes and FISPACT-II transmutation code. This enabled the rapid comparison of accelerator-driven production routes, while also executing the parsing and visualisation of data, enabling determination of the optimum target-beam combination, particle energy, and the time to chemically separate to maximise quantity and purity.

Quantitative results from this software package, along with coordination with the National Physical Laboratory on the potential chemical purification, \(^{nat}\)Mo(α, xn)\(^{97}\)Ru was determined to be the most promising reaction. This is due to the large cross-section of \(^{97}\)Ru production, high threshold energy of contaminant isotope \(^{99}\)Mo, and a novel separation scheme developed during this project which utilised the recently developed TK202 extraction chromatography resin.

A high-precision nuclear reaction cross-section method was developed for charged particle spectroscopy at the University of Birmingham MC\(_{40}\) cyclotron, including experimental set-up and semi-automated analysis software. This method was used to improve accuracy in nuclear reaction cross-sections for Mo-α, with the method and experimental results in this thesis.

Following this, a novel chemical separation method was developed at the National Physical Laboratory using TK202 resin. The optimum operating conditions were found to be 5M NaOH for a high retention of Tc. This enables easy separation of the Tc produced in the reaction from the \(^{97}\)Ru generator with a successive step extracting the \(^{97}\)Tc, produced through the decay of the tracer with a half-life of 2.83(32) d, from any stable Ru and Mo in the remaining target.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):

Supervisor(s)	Email	ORCID
Wheldon, Tzanka Kokalova	UNSPECIFIED	UNSPECIFIED
Wheldon, Carl	UNSPECIFIED	UNSPECIFIED
Russell, Ben	UNSPECIFIED	UNSPECIFIED
Ivanov, Peter	UNSPECIFIED	UNSPECIFIED