Speaker
Description
The future gamma-MRI imaging modality will allow the simultaneous exploitation the advantages of SPECT – sensitivity of gamma-ray detection, and MRI – spatial resolution and flexibility. The combination of these technique requires use gamma-emitting nuclei (like in SPECT) with highly polarized spins, leading to anisotropic emission of gamma-ray, and allowing spin manipulation with rf pulses (like in MRI).
An efficient production of 11/2 spin isomers $^{129m}$Xe (T$_{1/2}$=8.9 days), $^{131m}$Xe (T$_{1/2}$=11.8 days) and $^{133m}$Xe (T$_{1/2}$=2.2 days) is an important aspect of the gamma-MRI project. This contribution will present results of systematic studies of two production routes: at ISOLDE and in nuclear reactors. At ISOLDE, during four beamtimes in 2022 and 2023, we investigated the best production and implantation conditions. We used a UCx with plasma ion source and a cooled transfer line and implanted beams of different Xe isotopes inside the GLM chamber into aluminium and gold foils with and without beam sweeping for seconds and hours. We then compared the number of implanted ions and the activity of the samples determined with ISOLDE gamma detectors to our simulations based on the ISOLDE in-target yields [Michelon master thesis]. As a result, we could determine the isomeric ratio for 11/2 to 3/2 states and the total efficiency of xenon extraction from the target. The study will allow us to determine the best conditions to collect high-activity samples (> 10MBq) of $^{129m,131m,133m}$Xe.
The second method that we investigated in several campaigns between 2020 and 2023 to the production of $^{129m}$Xe and $^{131m}$Xe is based on neutron irradiation of highly enriched stable $^{128}$Xe and $^{130}$Xe samples in the high-flux nuclear reactors: RHF reactor at Institute Laue-Langevin (ILL, Grenoble, France) and MARIA reactor in the National Centre for Nuclear Research (NCBJ, Swierk, Poland). We developed and optimised experimental setups for efficient enclosure of stable Xe, extraction and characterisation of the produced xenon isomers. The results show that both reactors provide isomer activities sufficient for the project (> 50 MBq) with few unstable contaminants [M.Chojnacki et al, Applied Radiation and Isotopes – submitted 04/09/2023] .
The presentation will give a brief introduction to the gamma-MRI technique and will provide experimental details as well as results of xenon-isomer production at ISOLDE and at ILL and MARIA reactors.
