Dr Geoffrey Grime

“Total-IBA” implies the synergistic use of multiple IBA techniques. It has been claimed that Total–IBA inherits the accuracy of the most accurate IBA technique used. A specific example is now given of this where (in vacuo) EBS/PIXE of a glass sample uniform in depth is validated against absolutely calibrated EPMA of the same sample. The EPMA results had a mass closure gap of 2.0 ± 0.6 wt%; the full PIXE analysis determined the composition of this missing 2 wt%. The PIXE calibration was against a single certified glass sample, with uncertainties per line ~10%. Benchmarking also demonstrates ~10% underestimation of the Si scattering cross-section at proton energies ~3 MeV. But the Total-IBA determination of the silica content had a low standard uncertainty of about 2%. This is due to the strong constraints of both the chemical prior and also the mass closure properties of the EBS. Irradiation-induced sodium migration in this soda-lime glass is explored.

A "broadbeam" facility is demonstrated for the vertical microbeam at Surrey's Ion Beam Centre, validating the new technique used by Barazzuol et al. (Radiat Res 177:651-662, 2012). Here, droplets with a diameter of about 4 mm of 15,000 mammalian cells in suspension were pipetted onto defined locations on a 42-mm-diameter cell dish with each droplet individually irradiated in "broadbeam" mode with 2 MeV protons and 4 MeV alpha particles and assayed for clonogenicity. This method enables multiple experimental data points to be rapidly collected from the same cell dish. Initially, the Surrey vertical beamline was designed for the targeted irradiation of single cells with single counted ions. Here, the benefits of both targeted single-cell and broadbeam irradiations being available at the same facility are discussed: in particular, high-throughput cell irradiation experiments can be conducted on the same system as time-intensive focused-beam experiments with the added benefits of fluorescent microscopy, cell recognition and time-lapse capabilities. The limitations of the system based on a 2 MV tandem accelerator are also discussed, including the uncertainties associated with particle Poisson counting statistics, spread of linear energy transfer in the nucleus and a timed dose delivery. These uncertainties are calculated with Monte Carlo methods. An analysis of how this uncertainty affects relative biological effect measurements is made and discussed.

Sr/Ca and Mg/Ca ratios in biomineral CaCO3 have recently been regarded as more reliable than δ18O values as proxy for paleotemperature because they are less affected by salinity or polar ice volume. We argue, however, that vital effects can exert a greater control than paleotemperature over fossil Sr/Ca. Seasonal perturbations in isotopic data from the Eocene bivalve Venericardia planicosta reveal a gradually decreasing annual growth rate through ontogeny. High-resolution Sr/Ca ratios, analyzed with a new proton-microbe technique, increase markedly through ontogeny, however, suggesting that more Sr was incorporated as growth rate slowed rather than as a result of changing paleotemperature. Comparative δ18O and Sr/Ca data from the broadly coeval marine gastropod Clavilithes macrospira, which exhibits a linear growth rate through ontogeny, also shows a significant increase in Sr concentration with age as well as seasonal, possibly temperature-related variations. Our observations show that neither growth, calcification rate, nor temperature can be the sole factor controlling Sr incorporation into molluscan aragonite. Metabolic activity, related to factors such as temperature, salinity, age, and growth rate, is likely to exert the primary control over Sr/Ca ratios in aragonitic mollusks.

The Scanning proton microprobe uses a focused beam of MeV protons to give analytical information by exploiting two physical processes, particle induced X-ray emission (PIXE) and Rutherford Backscattering (RBS). Scanning transmission ion microscopy may also be included in the nuclear microscopy package to give imaging data. PIXE is particularly appropriate for biomedical research as signals from hydrogen, carbon, nitrogen and oxygen, which are the main components of a biological matrix, are not detected and therefore signals from inorganic elements with z > 10 will not be swamped by signals from the matrix. Elements with z < 10 can, however, be detected using RBS when present at higher concentrations. Apart from the biomedical field, the SPM has wide-ranging applications spanning diverse areas such as archaeology, materials science and environmental chemistry. This paper reviews the theory of ion beam analysis, the Oxford Scanning Proton Microprobe and outlines some of the work currently being carried out at Oxford.

The use of high energy ion beams (mainly of protons or alpha particles) for chemical analysis is described. The equipment necessary for achieving this is summarized. The main detection systems are proton-induced X-ray emission (PIXE), Rutherford backscattering (RBS) and nuclear reaction analysis (NRA). © 1999 Elsevier Ltd All rights reserved.

We demonstrate that the simultaneous combination of ion beam analysis (IBA) and ion beam induced luminescence (IL) can reveal valuable information concerning the performance of strained doped silica fibre thermoluminescence microdosimeters. The micron scale spatial resolution and low detection limits of IBA allow the lateral distribution of dopant elements to be mapped and then correlated with the distribution of prompt radioluminescence. Measurement of the decay of the IL signal with dose provide information concerning the saturation of the subsequent TL signal at high doses. MeV ion beams can deposit relatively high energy in localized, well-quantified small volumes and so this method is valuable for studying high dose effects in TL dosimeters. We describe a simple modification of the target chamber microscope which enables sensitive low background light detection in two wavelength bands and present preliminary results from three types of germanium doped silica fibre dosimeter.

Ion Beam Analysis (IBA) consists of a set of analytical techniques addressing elemental composition of inorganic material normally conducted using ion beams in the MeV kinetic energy range. Secondary Ion Mass Spectrometry using MeV ions (MeV SIMS) is the only IBA technique which can provide extensive molecular information about organic materials. MeV ions can be extracted into air hence offering the potential to apply MeV SIMS under atmospheric pressure. At the University of Surrey Ion Beam Centre, a fully ambient MeV SIMS setup has been developed and termed “Ambient Pressure MeV SIMS”. This AP MeV SIMS can be optimized for analysis and imaging of organic molecules. MeV SIMS relies upon electronic sputtering of the target material and this is much more efficient in insulating or organic targets, and less efficient in conducting metallic materials. PIXE, on the other hand, is efficient at providing good signals from elemental metallic systems, but does not readily provide molecular information from organics. The combination of the two techniques – preferably simultaneously with the same beam – provides useful complementary information which can readily be combined. Here we present pioneering preliminary work in simultaneous molecular and elemental imaging of a complex sample comprising of two organic species and two metallic species by combining AP MeV SIMS with Heavy Ion Particle Induced X-ray emission (HIPIXE).

Silver-staining "senile" plaques occurring in the brain are a major part of the pathology of Alzheimer's disease. The elemental composition of these structures, and the possible presence of aluminum and silicon in these structures, has been the subject of an increasing research effort over the last decade. However, the results have often been contradictory. Using a scanning proton microprobe, the elemental composition of senile plaques has been determined. This instrument, similar to an electron probe, uses a focused beam of protons scanned across a sample to map the elements. The technique is absolutely quantitative and is sensitive down to the parts per million level. Tissue from six cases of clinically and pathologically characterized cases of Alzheimer's disease and two aged neurologically normal controls was scanned. It was found that aluminum and silicon occur at a level of 50 ppm or greater in the cores of 20% of senile plaques and that the total occurrence of aluminum or silicon in scans containing plaques was not above background. The major uncertainties affecting interpretation of results of this kind are discussed, and it is suggested that the least controllable factor is contamination in the reagents used to prepare and stain the tissue. This indicates that until plaques can be unambiguously identified and analyzed in untreated tissue, no conclusion can be reached on whether senile plaques contain aluminum and silicon.

The quality of the structures fabricated using proton beam writing (PBW) and other direct-write microfabrication methods is strongly influenced by the path followed by the writing beam during the exposure. In particular, it is necessary to avoid paths in which the beam makes large jumps or changes in direction close to the edges of the structure, and ideally the scan path should follow the outline of the pattern to be exposed (sometimes referred to as turtle scanning). While this is relatively easy to implement when the patterns to be created can be built up from simple geometric shapes (circles, rectangles, etc), it has not been possible to do this in the case of arbitrarily complex images, at least using software available to the PBW community. This paper describes a simple edge-following algorithm (EFA) which uses a method of spiral searching around each pixel to determine a scan path which not only optimizes the conformity of the scan path to the edges of the required pattern, but also minimizes jumps (and hence blanking time) and scan reversals which can cause artefacts due to scanning system transients. The EFA operates on a 1-bit BMP format input image file and has been implemented in the OMDAQ-3 software package (Oxford Microbeams Ltd). The paper is illustrated with examples of complex structures written using the EFA at the University of Surrey Ion Beam Centre which demonstrate enhanced edge smoothness compared with simple blanked raster scanning.

The self-consistent Ion Beam Analysis (IBA) of cultural heritage samples using the external beam is technically demanding. We report on the calibration of an analysis of glass samples from the Rosslyn Chapel where the interest will ultimately be in the full characterisation of the weathered glass. Such an analysis requires a comprehensive Total-IBA approach using p-PIGE and He-PIXE to obtain ”bulk” and surface Na, with H-PIXE/EBS for multielemental depth profiling to 10 μm and He-PIXE/EBS for higher depth resolution near the surface; also with two PIXE detectors as usual for the high and low energy parts of the spectrum. A revised NDF v.10 code capable of a self-consistent handling of all these signals at state-of-the-art accuracy is described, together with the calibration protocols required for such an analysis. Other capabilities of the NDF code not previously discussed are also reviewed.

The principles of proton microprobe analysis are outlined and compared to electron beam analysis. Sample preparation methods are summarized, and the types of suitable sample are enumerated. The information that can be achieved from the analysis in terms of elemental composition and images is also described. © 1999 Elsevier Ltd All rights reserved.

The 12th International Conference on Proton Induced X-ray Emission (PIXE) and its Analytical Applications was held on the campus of the University of Surrey in Guildford, U.K. between 29 th June and 2nd July 2010. The PIXE conferences have been held at approximately three year intervals since the mid 1970s and have reflected the development of the PIXE technique and its expanding range of applications. This special issue of X-Ray Spectrometry contains papers based on conference contributions which have been selected to represent the latest developments in PIXE and its applications.

The suite of techniques which are available with the small accelerators used for MeV ion beam analysis (IBA) range from broad beams, microbeams or external beams using the various particle and photon spectrometries (including RBS, EBS, ERD, STIM, PIXE, PIGE, NRA and their variants), to tomography and secondary particle spectrometries like MeV-SIMS. These can potentially yield almost everything there is to know about the 3-D elemental composition of types of samples that have always been hard to analyse, given the sensitivity and the spacial resolution of the techniques used. Molecular and chemical information is available in principle with, respectively, MeV-SIMS and high resolution PIXE. However, these techniques separately give only partial information – the secret of “Total IBA” is to find synergies between techniques used simultaneously which efficiently give extra information. We here review how far “Total IBA” can be considered already a reality, and what further needs to be done to realise its full potential.