Proton Microbeam Research Articles

Magnetic signals of proton irradiated spots created on highly oriented pyrolytic graphite surface

We demonstrate that a proton microbeam produces ferromagnetic spots on highly oriented pyrolytic graphite surface. The micrometer wide spots were characterized by magnetic force microscopy . This technique reveals clear irreversible behavior of the magnetic signal at the spots after application of an external DC field. Our results leave no doubts on the intrinsic nature of the ferromagnetism in a metal-free carbon structure.

Imaging by using proton-induced quasi-monochromatic X-ray emission

Quasi-monochromatic X-ray emission induced by MeV-proton bombardment onto metallic targets was applied to radiography of small samples. The X-ray energy was adjusted in the range of ≈4–23 keV by changing the target material. The radiograms were recorded on an imaging plate. A small phantom made of Lucite was prepared for the test of photography using a contrast medium (RuCl3$H2O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Kα) which is slightly above the K-absorption edge of Ru at 22.12 keV. Only the image of the contrast agent was successfully extracted by subtracting the image taken by 21.18-keV X-rays (Pd Kα) from that obtained by the 23.17-keV photons. Also images of a small fish sample were taken using a point-like X-ray source excited by a proton microbeam with a diameter of ≈10 mm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Kα) to obtain a strong attenuation by Ca in the bones. A fine structure of the bones in the thin caudal fin (<100 mm) was highly contrasted by this method. The spatial resolution of the picture was ≈20 mm. Performance of the above technique based on the proton-induced quasi-monochromatic X-ray emission is discussed in comparison to conventional methods.

BEAM DAMAGE OF CELLULAR SAMPLES IN IN-AIR MICRO PIXE ANALYSIS

The change of shape and elemental concentration of cellular samples in In-Air micro PIXE analysis was investigated. Cultured bovine aortic endothelial cells were analyzed in the atmosphere by using 2.6 MeV proton micro-beams. The shape of cross-sections of cells was not so much distorted by beam irradiation and the concentrations of trace elements did not change too, except for S. The concentration of S changed with strongly depending on the temperature rise due to beam irradiation.

Assessment of proton microbeam analysis of 11B for quantitative microdistribution analysis of boronated neutron capture agents in biological tissues.

The (11)B(p,alpha)(8)Be* nuclear reaction was assessed for its ability to quantitatively map the in vivo subcellular distribution of boron within gliosarcomas treated with a boronated neutron capture therapy agent. Intracranial 9L gliosarcomas were produced in Fischer 344 rats. Fourteen days later, the majority of the rats were treated with f-boronophenylalanine and killed humanely 30 or 180 min after intravenous injection. Freeze-dried tumor cryosections were imaged using the (11)B(p,alpha)(8)Be* nuclear reaction and proton microbeams obtained from the nuclear microprobe at Lawrence Livermore National Laboratory. The (11)B distributions within cells could be imaged quantitatively with spatial resolutions down to 1.5 microm, minimum detection limits of 0.8 mg/kg, and acquisition times of several hours. These capabilities offer advantages over alpha-particle track autoradiography, electron energy loss spectroscopy, and secondary ion mass spectrometry (SIMS) for quantification of (11)B in tissues. However, the spatial resolution, multi-isotope capability, and analysis times achieved with SIMS are superior to those achieved with (11)B(p,alpha)(8)Be* analysis. When accuracy in quantification is crucial, the (11)B(p,alpha)(8)Be* reaction is well suited for assessing the microdistribution of (11)B. Otherwise, SIMS may well be better suited to image the microdistribution of boron associated with neutron capture therapy agents in biological tissues.

Local DNA damage by proton microbeam irradiation induces poly(ADP-ribose) synthesis in mammalian cells.

Cellular recovery from ionizing radiation (IR)-induced damage involves poly(ADP-ribose) polymerase (PARP-1 and PARP-2) activity, resulting in the induction of a signalling network responsible for the maintenance of genomic integrity. In the present work, a charged particle microbeam delivering 3.2 MeV protons from a Van de Graaff accelerator has been used to locally irradiate mammalian cells. We show the immediate response of PARPs to local irradiation, concomitant with the recruitment of ATM and Rad51 at sites of DNA damage, both proteins being involved in DNA strand break repair. We found a co-localization but no connection between two DNA damage-dependent post-translational modifications, namely poly(ADP-ribosyl)ation of nuclear proteins and phosphorylation of histone H2AX. Both of them, however, should be considered and used as bona fide immediate sensitive markers of IR damage in living cells. This technique thus provides a powerful approach aimed at understanding the interactions between the signals originating from sites of DNA damage and the subsequent activation of DNA strand break repair mechanisms

Temperature dependent TRIBIC in CZT detectors

Temperature dependence of the ion beam induced charge (IBIC) collection efficiency was studied in CdZnTe (CZT) in the range 166–330 K. A lateral surface between sputtered Au electrodes of the simple planar counter-grade CZT was irradiated by a focused 3 MeV proton microbeam. Measured charge collection efficiency profiles change with temperature. In order to understand better the charge collection mechanism at different temperatures time resolved ion beam induced charge (TRIBIC) technique was applied as well. Charge transients from the output of the preamplifier recorded by a fast storage oscilloscope showed that the electron transport is strongly influenced by temperature. Both IBIC and TRIBIC measurements showed negligible hole charge collection contribution in the studied detector.

Measurement of hydrogen concentration in thick mineral or rock samples

This paper describes an application of a proton–proton elastic recoil coincidence spectroscopy to hydrogen analysis using a proton microbeam at an energy of 20 MeV. This method provides depth profiles of hydrogen over a thickness of 200 μm of silicate samples in a short time. A typical beam size is as small as 27 × 32 μm. The depth resolution is about 10 μm. The present work proves that the proton–proton elastic recoil coincidence spectroscopy is a promising method for measurements of hydrogen in mineral and rock samples with thickness up to 200 μm.

In situ monitoring of polyimide windows for external ion microbeams

Damage of polyimide windows for external ion microbeams was monitored by analyzing backscattering protons from the window. A 1.5 MeV proton microbeam focused to approximately 50 × 50 μm 2 was transmitted through the polyimide window from vacuum to oxygen atmosphere. The changes in backscattering spectra of the window were monitored as a function of irradiation dose up to 2 × 10 18 H +/cm 2. For comparison, the polyimide window was irradiated in vacuum in the same way as the oxygen case. The backscattering spectra drastically changed in the case of oxygen. We observed that the carbon spectrum width, corresponding to the thickness of the window, substantially decreased with increasing the irradiation dose. The in situ monitoring of backscattering protons demonstrated the ability to detect the damage of the window and to predict the rupture of the window.

Ion and X-ray micro-beam induced charge collection and their applications in CVD diamond detector characterisation

We have used a micrometer size X-ray beam generated from a synchrotron light source at the European Synchrotron Radiation Facility (ESRF) in Grenoble and a 2 MeV proton micro-beam at the Italian National Laboratory (LNL) of Legnaro to image the electronic transport properties of a CVD diamond detector developed within the CERN RD42 collaboration. The focused X-rays or protons are scanned over the device surface, and the induced current or charge pulse is measured and plotted on two dimensional maps. Due to the polycrystalline nature of the material, the maps are not homogeneous and both the techniques show structures ascribable to diamond grains. It was found that the uniformity of the maps depends on the lateral scale (binning) and on the analytical depth of the micro-probes.

Blue light sensitization of CVD diamond detectors

CVD diamond needs to be ‘primed’ or ‘pumped’ by X-rays or by high energy electrons in order to be qualified for nuclear detection. In this ‘pumped’ state, CVD diamond detector performances are reported to be more reproducible, homogeneous and averagely better. The pumping effect is usually attributed to filling of (hole) traps, which are responsible for the charge collection efficiency of the detector. In this work, the possibility of filling traps selectively by light has been systematically investigated, in order to find the kind of ‘background light’ in which the detectors could preserve their performances indefinitely in time. Irradiation by the blue light before or/and during the detection of nuclear particles seems to avoiding the large doses needed for pumping. Other wavelengths seem to be totally inefficient from this point of view. It turns out that electrons are responsible for charge transport during blue light priming, while holes give the largest contribution during X-ray priming. The results will be presented as maps of charge collection efficiency in CVD diamond detectors as obtained by IBIC (Ion Beam Induced Charge) carried out by using a proton microbeam.

Nuclear microprobe analysis of U-doped (Bi,Pb) 2Sr 2Ca 2Cu 3O y/Ag superconducting tapes

Superconducting (Bi,Pb) 2Sr 2Ca 2Cu 3O y /Ag tapes are doped with uranium compounds to introduce flux pinning defects from neutron-induced fission. The composition and distribution of elements in cross sections of the tapes were probed with a scanned 3 MeV proton microbeam using proton induced X-ray emission (PIXE). Distributions of the constituent elements were found to be heterogeneous on a scale of 10 μm. By combining the PIXE analysis with Rutherford backscattering spectrometry, the stoichiometry of the superconductor within the tape was measured, including oxygen from elastic scattering, revealing a departure from the desired 2223 composition. In one of the tapes, PIXE elemental maps of the Ag distribution showed diffusion of Ag into the superconductor from the enclosing jacket. Crystals of the same material, not fabricated into tapes, did not contain the contaminants and had a more ideal stoichiometry. Correlation maps between the constituent elements, deduced from the elemental maps, indicate the presence of secondary or unreacted phases.

IN-AIR MICRO-PIXE ANALYSIS OF TISSUE SAMPLES

Micro-PIXE is capable of providing spatial distributions of elements in the micro-meter scale and its application to biology is useful to elucidate the cellular metabolism. Since, in this method, a sample target is usually irradiated with proton or α-particle beams in vacuum, beam heating results in evaporation of volatile elements and shrinking of the sample. In order to avoid these side effects, we previously developed a technique of in-air micro-PIXE analysis for samples of cultured cells. In addition to these, analysis of exposed tissue samples from living subjects is highly desirable in biological and medical research. Here, we describe a technique of in-air micro-PIXE analysis of such tissue samples. The target samples of exposed tissue slices from a Donryu rat, in which a tumor had been transplanted, were analyzed with proton micro-beams of 2.6 MeV. We report that the shape of cells and the distribution of volatile elements in the tissue sample remain uncharged when using a target preparation based on a freeze-drying method.

Geological Studies by Means of Proton Microbeam System

Features necessary to make a scanning nuclear microprobe a useful tool in geological studies are summarized and its present position among other microanalytical techniques is reviewed.

Chromium mapping in male mice reproductive glands exposed to CrCl 3 using proton and X-ray synchrotron radiation microbeams

Preconception exposure to certain chemicals may increase risk of tumors in offspring, especially with regard to occupational metals such as chromium. However, the mechanism of chromium trans-generation carcinogenicity remains unknown. Using scanning proton X-ray microanalysis we have been able to detect chromium in testicular tissue sections from mice treated by intraperitoneal injection of 1 mmol/kg CrCl 3. Chromium concentration was about 5 μg/g dry mass in average, but higher concentrations were found within the limiting membrane of the testes, the tunica albuginea. In addition, synchrotron radiation X-ray fluorescence measurements, with microscopic resolution, clearly demonstrated the presence of chromium in the tunica albuginea but also within isolated cells from the interstitial connective tissue.

Cytological and histological structures identification with the technique IBIL in elemental microanalysis

Ion beam induced luminescence (IBIL) is applied to the inspection of histological and cytological specimens, dried and placed in vacuum. It is shown to offer a way for a precise aiming of a proton microbeam on the sample for a subsequent traditional microanalysis. We used the nuclear microprobe of the Laboratori Nazionali di Legnaro and its IBIL facility to identify biostructures stained with some usual fluorescent dyes, capable of discriminating tissues and cells of different nature or different parts of a cell. To this purpose we produced low dose IBIL maps of the region of interest, employing a high sensitivity light detector. We describe the experimental set-up, propose a peculiar support for specimens, specify the properties of few widespread used staining procedures and evaluate their IBIL emission.

Microbeam studies of gel–polymer interfaces with Li anode and spinel cathode for Li ion battery applications using PIGE and PIXE spectroscopy

Characteristics of Li ion batteries depend on resistance at interfaces of gel–polymer electrolyte with Li anode and with spinel cathode, respectively. Interfacial resistances are correlated to the spatial distribution of Li and other chemical species in vicinity of interfaces of gel–polymer with cathode or anode. Studies of gel–polymer interfaces in Li ion battery semicell samples (Li-anode/gel–polymer and spinel LiMn 2O 4 cathode/gel–polymer) have been performed by proton microbeam scans over the sample cross-section. PIGE spectroscopy has been used for Li and F detection and PIXE spectroscopy for detection of S, Mn and other elements of interest.

Influence of electrical contacts on charge collection profiles in CdZnTe studied by IBIC

The lateral and frontal modes of the nuclear microprobe technique ion beam-induced charge collection (IBICC) were used for imaging the electronic properties of CdZnTe room-temperature detectors. The detectors with different contacts (In–In, In–Au, Au–Au) were bombarded with a scanned 4 MeV proton microbeam. By measuring the detector response at bias voltages of up to several hundred volts, charge collection profiles along the thickness of a detector were calculated for different shaping times . Obvious differences between the various contacts were observed in lateral IBICC efficiency profiles that varied in shape, height and smoothness. No hole collection contribution was observed at apllied voltages for all three configurations of the CZT detector. Electron mobility–lifetime products were calculated from measured IBICC efficiency profiles.

Studies of physiology and the morphology of the cat LGN following proton irradiation

Purpose: We have examined the effects of proton irradiation on the histologic and receptive field properties of thalamic relay cells in the cat visual system. The cat lateral geniculate nucleus (LGN) is a large structure with well–defined anatomical boundaries, and well–described afferent, efferent, and receptive field properties. Methods and Materials: A 1.0-mm proton microbeam was used on the cat LGN to determine short-term (3 months) and long-term (9 months) receptive field effects of irradiation on LGN relay cells. The doses used were 16-, 40-, and 60-gray (Gy). Results: Following irradiation, abnormalities in receptive field organization were found in 40- and 60-Gy short-term animals, and in all of the long-term animals. The abnormalities included “silent” areas of the LGN where a visual response could not be evoked and other regions that had unusually large or small compound receptive fields. Histologic analysis failed to identify cellular necrosis or vascular damage in the irradiated LGN, but revealed a disruption in retinal afferents to areas of the LGN. Conclusions: These results indicate that microbeam proton irradiation can disrupt cellular function in the absence of obvious cellular necrosis. Moreover, the area and extent of this disruption increased with time, having larger affect with longer post-irradiation periods.

The use of proton microbeams for the production of microcomponents

The recently developed process of high-energy ion beam micromachining (proton micromachining) is discussed. Proton micromachining is a novel process for the production of high aspect-ratio 3D microstructures. The sub-micron lateral resolution and the well-defined range of an MeV proton microbeam are utilized to make lithographic structures in suitable polymers (e.g., SU-8, PMMA). Sub-micron structures with a depth of tens of microns and aspect-ratios approaching 100 have been achieved. The use of different energies for multiple exposures allows the production of intricate 3D multi-layer structures in a single polymer layer, and because no mask is needed the process offers a wide range of possible geometries for the production of non-prismatic or even rounded features. The throughput of the technique does not compare favourably with conventional (masked) processes for high volume batch production of microcomponents. On the other hand, significant applications of high-energy ion beam micromachining may be developed, e.g. for the rapid production of prototypes, the research into the characteristics of microstructures, and the manufacture of molds, stamps and X-ray masks.

Study of Italian Renaissance sculptures using an external beam nuclear microprobe

The use of an extracted proton micro-beam for the PIXE analysis of glazes is discussed in the context of the growing interest in the creation of an analytical database on Italian Renaissance glazed terracotta sculptures. Some results concerning the frieze of an altarpiece of the Louvre museum, featuring white angels and cherubs heads, are presented.