Development of a Neutron Activation Analysis station at the Lund Ion Beam Analysis Facility

Abstract

This report outlines the first stages of the development of the Neutron Activation Analysis station at the Lund Ion Beam Analysis Facility in the Division of Nuclear Physics, Lund University. The motivation for this project is to use the Neutron Activation Analysis detection technique for environmental monitoring around the European Spallation Source, soon to come into operation. In the event of an emergency scenario, some radiotoxic isotopes may be released into the environment from the Tungsten spallation target, including the difficult to detect lanthanide, 148Gd. In normal operation, a variety of radionuclides may also be released. In this initial stage, the aim was to build a measurement station which is able to measure very short-lived activation products, and to investigate if it is possible to trace gadolinium isotopes in environmental samples using neutron activation analysis.

The measurement station was constructed over the span of one semester, and a selection of metal foils and environmental samples were activated and analysed. The samples were irradiated using a portable neutron generator with a maximum production rate of 4.71 ·10E8 n/s. Two methods of measurement were utilised: one which used irradiation- and measurement- times of longer than one hour, and another which used a fast pneumatic transport system with irradiation- and measurement-times of less than 1 minute. High Purity Germanium detectors were used to measure the γ-rays emitted from the activated samples. Results showed that with the selection of tested samples, it was possible to measure activation products with half-lives as short as two seconds using the fast pneumatic line. In the environmental samples, it was seen that amounts larger than several grams were needed in order to see activation and that longer irradiation time was more suitable. The results obtained show that the station has the potential to be developed for use with the Compact Accelerator-driven Neutron Source under development at the facility, which is anticipated to achieve a neutron production rate of 10E11 n/s.

Popular Abstract

Scientists have been dating ancient pottery and other relics for decades, to uncover the stories of lost civilisations and forgotten traditions. Of the methods used, it turns out that it is a nuclear technique which best preserves these valuable pieces of history, while other techniques risk destroying them. The process, called ​Neutron Activation Analysis, (NAA), can not only find when and where a sample is from, but exactly what isotopes it is made up of.

NAA involves ‘activating’ a chosen sample – an old pot, for example – by blasting it with billions of neutrons, until it becomes radioactive. The atoms in the pot absorb the neutrons, and their nuclei become unstable, quickly ejecting high energy electromagnetic waves called gamma rays, to reach stability again. The frequencies of the gamma rays are unique to
each isotope and can be analysed to uncover it’s exact composition, and when and where it has been. The pot could remain radioactive for several days or weeks afterwards, but can eventually be safely returned to its owner.

For example, a leading research scientist at Imperial College London, Judit Nagy, was able to use neutron activation analysis to date ancient Hungarian pottery to unearth the trade routes travelled by early European merchants. This technique is also used all the time in present day investigations too. Because NAA can reveal even minute traces of an isotope, materials such as bullet fragments, gunshot residue, DNA, and poison can be identified, rendering NAA particularly useful in forensic science and criminal investigations.

In the wake of the climate crisis, a further important application of NAA is environmental monitoring. Samples such as soil, plants and sediment can be analysed to assess the health of a particular environment. From this, we can see where human activities are causing harmful effects on ecosystems and learn the origins of pollution.

One issue that scientists run into with NAA, is that in order to get a high enough blast of neutrons, the sample usually needs to be placed into a special chamber in a nuclear reactor, which must then be moved to an analysis facility, such as a research centre or university. As you might imagine, transporting a highly radioactive sample is tricky. Furthermore, some of the radioactive isotopes created by activation decay so quickly, that any time delay between activation and analysis would mean that those isotope traces are lost.

Lund University has recently obtained a neutron generator; although it is far smaller and less powerful than a reactor, it should generate just enough neutrons to activate the samples. For my degree project, I will lay the groundwork for the setup of Lund University’s own NAA facility, where both the activation and analysis are in immediate proximity. In the future, the University will be able to develop the setup to be suitable for environmental monitoring at the European Spallation Source in Lund, the world’s most powerful neutron generator, due to open in the coming years. Once up and running, Lund University will be able to better analyse pollution, monitor the environment, and even date your ancient pot.

• author: Lindsey-Clark, Josephine
• supervisor: Robert Frost
• organization: Nuclear physics; Department of Physics
• course: FYSK02 20202
• year: 2021
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: Neutron Activation Analysis, NAA, European Spallation Source, ESS, Lund Ion Beam Analysis Facility, LIBAF, Gamma-Ray Spectra
• language: English
• id: 9038694
• date added to LUP: 2021-01-29 15:54:19
• date last changed: 2021-01-29 15:54:19