At the Tip of an MeV Beam: Provoking Cells and Performing Tomographic Imaging

Abstract

Biological applications of ion beams have recently become a new important research field using single ion hit facilities to study individual living cells and their response to the hit of a counted number of ions. One motivation is the search for a better understanding of the fundamental processes taking place in cells and organs as a result of irradiation. Another comes from the increasing interest in using high energy protons and heavy ions as a modality for radiotherapy of deep seated tumours. In the view of treatment efficiency, study of cell culture behaviour under controlled radiation experiments, and in different chemical environments at single ion hit facilities, is a first step towards a better understanding of the processes. Tomographic techniques are applicable to situations where you need information of the inside of an object but do not want to section it into thin slices or cannot do it. Using focused MeV ion beams for tomography restricts the sample size to the order of 10-100 µm, depending of the initial energy. On the other hand, the ability to focus at a sub-micrometer level makes ion beams well suited for analyses of small sized objects as cells, spores, etc. The scanning transmission ion microscopy mode of tomography gives the mass density and corresponding morphological structure of holes and pores. It can then be used to correct the results from the other mode, particle induced X-ray emission tomography. Here is discussed a porosity analysis of bentonite clay that is planned to form an important buffer zone around canisters filled with spent nuclear reactor fuel waste deposited 500 m underground in Sweden. Development of irradiation facilitiesDuring the recent years there has been a European move towards developing high resolution ion beam facilities to be used in the study of cellular responses to single ion hits [1,2]. Those systems utilise the counted, localised and focused MeV ions to interact with monolayer biological experimental systems to induce localised, quantified damage with the purpose to study the biological effects originating from the interaction. It has since more than a decade been a research field in the borderland between physics and biology [3,4] and today a considerable number of single ion hit facilities have been developed worldwide (see e.g. [5,6]). A single ion hit facility (SIHF) is a modified nuclear microprobe specially adopted for the task of shooting single, positioned ions [7].Many experiments focus on the effects of low dose irradiation: bystander effect, genomic instability and adaptive responses [8]. There are several phenomena that * corresponding author; e-mail: Jan.Pallon@nuclear.lu.se are not well understood, e.g. the limits for double-strain breaks, cell-to-cell communication and interactions that indicate both increased sensitivity versus radiation as well as increased protection against radiation (adaptative response). This type of experiments can hardly be done without the use of well controlled ion exposures (local energy transfer to the cell, num...