Effects of X-ray dose on rhizosphere studies using X-ray computed tomography

X-ray Computed Tomography (CT) is a non-destructive imaging technique originally designed for diagnostic medicine, which was adopted for rhizosphere and soil science applications in the early 1980s. X-ray CT enables researchers to simultaneously visualise and quantify the heterogeneous soil matrix of mineral grains, organic matter, air-filled pores and water-filled pores. Additionally, X-ray CT allows visualisation of plant roots in situ without the need for traditional invasive methods such as root washing. However, one routinely unreported aspect of X-ray CT is the potential effect of X-ray dose on the soil-borne microorganisms and plants in rhizosphere investigations. Here we aimed to i) highlight the need for more consistent reporting of X-ray CT parameters for dose to sample, ii) to provide an overview of previously reported impacts of X-rays on soil microorganisms and plant roots and iii) present new data investigating the response of plant roots and microbial communities to X-ray exposure. Fewer than 5% of the 126 publications included in the literature review contained sufficient information to calculate dose and only 2.4% of the publications explicitly state an estimate of dose received by each sample. We conducted a study involving rice roots growing in soil, observing no significant difference between the numbers of root tips, root volume and total root length in scanned versus unscanned samples. In parallel, a soil microbe experiment scanning samples over a total of 24 weeks observed no significant difference between the scanned and unscanned microbial biomass values. We conclude from the literature review and our own experiments that X-ray CT does not impact plant growth or soil microbial populations when employing a low level of dose (<30 Gy). However, the call for higher throughput X-ray CT means that doses that biological samples receive are likely to increase and thus should be closely monitored

Ion beam analysis of molecular diffusion in heterogeneous materials.

Scanning ion micro-beam analysis has been used to determine the diffusion of molecules in materials with a combination of high spatial resolution and concentration sensitivity not possible with other analytical techniques. The ion beam analysis apparatus and techniques available at the University of Surrey are described. Methodologies have been devised to determine the scanning micro-beam line scan size and the diameter of the beam spot. Adaptations to the micro-beam line hardware have been proposed with the design of a novel form of none interrupting beam current monitor utilising a transmission Faraday cup and charge collection from the object aperture. Micro-Nuclear Reaction Analysis (NRA) has been used for the first time to resolve the location and concentration of a hydrocarbon molecule in a biological matrix. Deuterated molecules (a surfactant and a hair conditioning agent) were imaged in perm damaged and undamaged hair fibres. Natural deuterium levels were ascertained with reference to a virgin hair fibre. Profiles of chlorine diffusing into cement paste blends have been determined using micro-Particle Induced X-ray Emission (PIXE). The profiles were fitted with a semi-infinite model of Fickian diffusion. The analysis was combined with micro-NRA to simultaneously profile the aqueous carrier (deuterium oxide) with the diffusing chlorine. A combination of micro-PIXE and micro-NRA has been used for the first time to image the ingress of water (deuterium oxide) and subsequent redistribution of drug in a polymeric drug release system. The two dimensional distributions of water, drug, and polymeric matrix are statistically correlated

Ion beam analysis of molecular diffusion in heterogeneous materials.

Scanning ion micro-beam analysis has been used to determine the diffusion of molecules in materials with a combination of high spatial resolution and concentration sensitivity not possible with other analytical techniques. The ion beam analysis apparatus and techniques available at the University of Surrey are described. Methodologies have been devised to determine the scanning micro-beam line scan size and the diameter of the beam spot. Adaptations to the micro-beam line hardware have been proposed with the design of a novel form of none interrupting beam current monitor utilising a transmission Faraday cup and charge collection from the object aperture. Micro-Nuclear Reaction Analysis (NRA) has been used for the first time to resolve the location and concentration of a hydrocarbon molecule in a biological matrix. Deuterated molecules (a surfactant and a hair conditioning agent) were imaged in perm damaged and undamaged hair fibres. Natural deuterium levels were ascertained with reference to a virgin hair fibre. Profiles of chlorine diffusing into cement paste blends have been determined using micro-Particle Induced X-ray Emission (PIXE). The profiles were fitted with a semi-infinite model of Fickian diffusion. The analysis was combined with micro-NRA to simultaneously profile the aqueous carrier (deuterium oxide) with the diffusing chlorine. A combination of micro-PIXE and micro-NRA has been used for the first time to image the ingress of water (deuterium oxide) and subsequent redistribution of drug in a polymeric drug release system. The two dimensional distributions of water, drug, and polymeric matrix are statistically correlated

Non-ionic surfactant concentration profiles in undamaged and damaged hair fibres determined by scanning ion beam nuclear reaction analysis

Nuclear Reaction Analysis (NRA) was used with a scanning MeV He-3 ion microbeam to determine the extent of permeation and segregation of a deuterated non-ionic surfactant (dC(12)E(5)) into virgin (undamaged) and alkalinic perm damaged hair fibres. 2-D concentration maps show an accumulation of deuterated surfactant in the cortex and medulla of both the virgin and damaged hair. By normalising to the matrix carbon, surfactant levels in the damaged hair were found to be three times higher than in the undamaged hair. This is the first reported direct spatial evidence of the penetration of surfactant into the centre of hair fibres. Furthermore it is the first application of NRA to this type of complex biological matrix. (C) 1997 Elsevier Science B.V