International Journal of PIXE

An ion beam induced luminescence analysis system using ion micro-beam (micro-IBIL) was newly developed on the microbeam system of the 3 MeV single-ended accelerator at ion-irradiation research facility TIARA, JAEA. The developed IBIL system consisted of an aspheric microlens, optical fibers, a monochromator and a photon-counting system to observe IBIL photons of specific wavelength with the resolution of 2 nm. A photomultiplier in the photon-counting system was cooled to around 0°C by a peltier device to reduce the background noises down to 10 cps and able to observe weak photon signals from specific chemical composites of the target. Experiments of micro-IBIL were performed using 3 MeV proton microbeam for several scintillators and particulate targets i.e. aerosol particles. The system had achieved chemical-imaging of aerosols by obtaining wavelength-dispersive micro-IBIL image at luminescence center of silicon dioxide.

A standard-free method for living plants in in-air PIXE has been developed in order to clarify the mechanism of elemental transportation and movement in farm products. The components of the continuous X-rays originated from air and a backing film can be exactly subtracted using a blank spectrum after normalization by the yields of Ar Kα X-rays. It is found by observing the yield of continuous X-rays with passage of time that water content is continuously decreasing during irradiation with a proton beam in a case of pinched leaves. In contrary, it is kept almost constant during irradiation for the living plants to which water is continuously provided through the roots. Stability of the yield of continuous X-rays is a required condition for a standard-free method, which makes use of the yield of continuous X-rays mainly emitted from water content. It is confirmed that potassium concentration shows no large position dependence on a leaf, and it keeps almost constant during irradiation, which also indicates that regular metabolism is going on. As potassium is always contained in all kinds of plants in large amount, it is designated as an index element. As a result, it is found that the potassium concentration obtained by the present standard-free method shows quite consistent values with those obtained by the internal-standard method. The present method is confirmed to be quite useful for investigating movement of not only toxic elements but also essential elements reflecting metabolism in plants.

For quantitative measurements of light elements by micro-PIXE (particle-induced X-ray emission) analysis, suitable external standards have been expected. In this paper thin sections of polyvinyl alcohol solution containing phosphorus (P) and potassium (K) were assessed for their purpose as standards by micro-PIXE analysis. Homogeneity of P and K added to the standard materials were validated by 1 μm and 10 μm-step scanning of the standard. The relative standard deviations of the X-ray intensity of the standards P and K were < 25% and <16%, respectively. The calibration line between the X-ray intensity obtained from a 100 × 100 μm² area and the elements concentration was also acceptable, indicating that the thin section standards are adequate for an external standard of micro-PIXE measurements for light elements.

Fluoride (F) distribution in human teeth was measured using an in-air micro-PIGE and micro-PIXE system. Class V cavities in the extracted teeth were prepared with Fluoro-Bond Shake One to provide a thin layer of an F-releasing material (FRM). The cavities were then filled with Beautifil Flow F10 (FRM, Group I) or LITE FIL IIP (non-FRM, Group II). Following a four-year period, specimens were cut longitudinally perpendicular to the cavity floor. The F distribution was measured at the floor of the cut surface. The position including 90% of the intact Ca level was defined as the wall surface. Based on this demarcation, indices of F distribution (surface F concentration and F penetration depth) were determined. Thickness of FRM thin layers varied (≈339 μm) and did not affect F distribution. Both values of F distribution indices in Group I [821–8763 (mean 3797) ppm, 34–668 (mean 241) μm] were significantly larger than those in Group II [0–7064 (mean 1865) ppm, 0–143 (mean 21) μm]. The F distribution in Group I was affected more by the filling material than by the FRM thin layer during the four-year exposure. Methodologies using this system may give insightful information for the development of new dental materials.

Microencapsulated anti-RLIP76 was tested in vivo using C3He/J mice to determine the increasing of antitumor effects by chemotherapeutic agent efflux inhibition during chemoradiotherapy. Microcapsules were produced by spraying a mixture of 3.0% hyaluronic acid, 2.0% alginate, 3.0% H₂O₂, and 0.3 mmol carboplatin onto a mixture of 0.3 mol FeCl₂ and 0.15 mol CaCl₂. Microcapsules were subcutaneously injected into MM46 tumors previously inoculated into the left hind legs of C3He/J mice. Subsequent radiotherapy consisted of tumor irradiation with 10 Gy or 20 Gy⁶⁰Co. The antitumor effects of microcapsules were tested by measuring tumor size and monitoring tumor growth. Three types of adverse effects were considered: fuzzy hair, loss of body weight, and mortality. Carboplatin levels were monitored using particle-induced X-ray emission (PIXE) and a micro-PIXE camera. Anti-RLIP76 inhibited the efflux of carboplatin from tumor tissue, which led to an increase in the concentration of carboplatin. Higher carboplatin concentration significantly increased the combined antitumor effect of radiation and chemotherapy. A significant decrease in adverse effects was also observed with microencapsulated anti-RLIP76.

Investigation of the radiation-induced bystander effect plays an important role in the understanding of the mechanisms of radiation response after low-dose irradiation. Sphingomyelinase (SMase) was activated by radiation and required the metal element for its activation. For further elucidation of the bystander effect, we investigated the relationship between its induction by acid SMase and a factor secreted from the irradiated tumor cells. In the cell culture medium transfer experiment after irradiation at a dose of 0.1 Gy, cell death was induced in non-irradiated cells. However, when cells received prior treatment with SMase inhibitor, cell death was not induced. When fluctuations in the activation of SMase and metal elements were detected, both intracellularly and extracellularly after irradiation, an increase in SMase activity and Zn concentration occurred within the cells at 5 min and outside of the cells at 15 min after irradiation. This increase in zinc concentration at 15 min after irradiation was suppressed by treatment with SMase inhibitor. These results suggest that activation of SMase, which is related to the bystander effect, is dependent on zinc.

The chemical speciation of chlorine (Cl) in particulate matter samples produced by the laboratory burning of organic Cl compounds was tested by employing the high-resolution measurement of Kβ X-rays based on a wavelength-dispersive proton-induced X-ray emission (WD-PIXE) technique. Targets for proton irradiation were prepared by depositing particulate burning products on aluminum foils placed on a simple barrel burner. Standard inorganic (NaCl, MgCl₂, CaCl₂, NH₄Cl, and AlCl₃) and organic (polyvinyl chloride and polyvinylidene chloride) Cl compounds were prepared for spectral comparison. We found that the Cl-Kβ₁ peak energies for these organic compounds are higher by approximately 1 eV than those for inorganic compounds. For burning products of these organic compounds, the peak energies were found to be located between those for organic and inorganic compounds. This result indicates that the organic Cl compounds were decomposed to smaller molecules during the burning process but these fragments still existed in the organic form.