International Journal of PIXE

A new procedure for the investigation of acrylic paint layers superposed on an aluminim foil has been recently suggested. The experimental technique consisted in a series of PIKE analyses at various incident proton energies. The sequence of colours and the thicknesses of the layers were established very satisfactorily.

Here, we apply this technique to a painting made with six acrylic colours from Liquitex Inc. Analyses at various points yield a good agreement with the information given by the painter. In this article we report on the results obtained for one of the points and we present and discuss the ingredients required by the computation.

Proton induced X ray emission analysis results are reported for obsidian artifacts from different sites of the State of Mexico: Teotenango, Calixtlahuaca, La Marqueza, Malinalco and Tonatico. Twenty elements were analysed by PIXE and some of them were verified by AAS. The results show that the samples came from three different sources: Teotenango and Calixtlahuaca samples from the first, La Marqueza and Malinalco samples from the second and Tonatico samples from the third.

Ca-DTPA or Zn-DTPA was injected subcutaneously to pregnant mice once a day for 5 consecutive days from the 13th day to the 17th day of gestation. Maternal and fetal livers were collected 20 hours after the final injection of DTPA, and essential metal contents in the liver samples were determined by PIXE.

Both Ca-DTPA and Zn-DTPA don't affect any essential metals in the maternal liver, but Ca-DTPA decreases copper and zinc contents in the fetal liver to 2/3 and 1/2 of the control values, respectively. Although Zn-DTPA does not affect fetal zinc content, it decreases that of copper. It could not be determined whether DTPA affects fetal manganese content or not because the fetal liver contains no detectable amount of manganese.

A metal-preconcentration procedure, which consists of a combination of chelation by dibenzyldithiocarbamate ions with subsequent condensation into dibenzylidene-D-sorbitol gels, has been reformed by using Zr as an internal standard. The colloidal gels formed in solutions were collected on a nuclepore filter for direct irradiation by 3 MeV proton beams in a system of vertical beam type in-air PIXE. The methodology was tested for simultaneous determination of the concentrations of seven metals (Fe, Co, Ni, Cu, Cd, Hg, Pb) in 25 ml of an aqueous sample. A good linear relationship was obtained between the nominal concentration and the elemental X-ray yields normalized with Zr-K_α ones. Absolute values of concentration in the sample solutions can be determined with an experimental error less than ±14 % in the 5-100 ppb range by employing published data pertinent to the inner shell ionization and subsequent X-ray emission of the heavy metals.

PIXE, Particle Induced X-ray Emission, is a Powerful, multi-elemental analysis method which has many distinguishing features and has been used in varies research fields. Recently the method of applying baby cyclotrons for nuclear medicine to PIXE has been developed. This enables us to study biomedical phenomena from the physical point of view. Mouse bone marrow stromal cells were transferred bacterial β -galactosidase gene (LacZ gene) by murine retroviral vectors. Analysis of the bone marrow stromal cells with the LacZ gene by PIXE revealed remarkable changes of intracellular trace elements compared with the normal control cells. These results indicate that gene transfer by retroviral vectors may bring about a dynamic change of intracellular circumstances of the target cell.

A 60-year-old female was hospitalized because of anemia, edema, and diarrhea. She was diagnosed as having short bowel syndrome. The patient developed acrodermatitis enteropathica and taste impairment. Laboratory data showed that the serum zinc level was 21 μ g/dl and erythrocyte CAI specific activity was 0 units/mg isozyme (normal range 0.37 ± 0.08 units/mg isozyme) and CAII specific activity was 2.99 units/mg isozyme (normal range 3.02 ± 0.05 units/mg isozyme). The patient was diagnosed as being in a zinc deficient status. Zinc supplementation resulted in the disappearance of these complications. The serum zinc level reached 50 μ g/dl and erythrocyte CAI specific activity was recovered to 0.26 units/mg isozyme and CAII specific activity was 1.60 units/mg isozyme. CAI is found in gastrointestinal epithelial cells, in vascular epithelium, corneal, lens, ciliary body epithelium, and in sweat glands. CAII is found in virtually all tissues and is especially abundant in secretory and absorbing epithelia. The tissue distribution of CAI corresponds to clinical and physiologic indicators of zinc deficiency. Thus, the erythrocyte CAI specific activity may reflect the actual tissue zinc deficiency status.

The X-ray analysis techniques of X-ray Fluorescence (XRF) and Particle-Induced X-ray Emission (PIXE) were tested for their sensitivity, precision, and accuracy in conducting elemental analyses on feathers. XRF could detect 21 elements directly in the sample matrix with minimum detectable limits of 0.5 to 1 μg/g for most elements. Due to the feather's thickness, a correction factor was applied to account for X-rays absorbed within the sample matrix. To confirm the results obtained by XRF, atomic absorption spectroscopy was conducted for mercury on four samples analyzed by XRF and the results were consistent between the two analytical techniques. The feathers, which ranged from 3 to 7 mg/cm² in areal density, proved too thick for straightforward analysis by PIXE. While corrections could have been applied, the feather's structure makes the task difficult and the beam attenuation correction would compound the already large X-ray absorption correction factor.

The XRF system was then tested for its effectiveness in two field studies. The first project used XRF to determine geographic differences between two populations of brown pelicans where nine of the fourteen elements routinely detected varied between the populations. The second project used XRF to trace mercury contamination in birds at Clear Lake, CA. The feathers showed elevated mercury concentrations while other potential contaminants were low.

Nuclepore filters have been widely used for collecting atmospheric aerosols and such samples are quite convenient for PIXE since they can be analyzed without any treatment. However, some special methods, (which is somewhat different from existing standard methods for general samples), must be applied in order to perform quantitative analysis. We have developed a method of quantitative analysis for all elements making use of bromine, which is almost uniformly contained in general Nuclepore filters, as an internal standard. Then, for quantitative analysis of light elements, the standard-free method, which makes use of total yield of continuous x-rays, has been applied and it is found that this method can be successfully applied to practical aerosol samples. Moreover, the method was applied to bio-samples prepared by cutting frozen samples with a microtome, and the result is almost satisfactory. It is found that the present method can be successfully applied to any sample which can be made uniform.

The PIXE facility at Tokyo Metropolitan Isotope Research Canter is described. This system allows for one-man total operation including accelerator control. A sample up to 100mm square can be set on the sample target which enable us to bombard arbitrary 36 points on the sample with proton. PIXE spectra are collected automatically using a computer which also controls the position of the sample holder. The facility is suitable for analysis of environmental samples and biological samples.

Elemental composition of living cells and tissues reflects their physiological function and status. However, it has been difficult to know in-situ elemental distribution by conventional analytical methods. In-air PIXE seems suitable for surface analysis of living cells and tissues because any treatment (e.g. freeze drying, digestion) is not required before and during measurement. We applied Via (vertical-beam in-air) PIXE to surface analysis of plant roots exposed to aluminum (Al). Aluminum stress is a major factor that limits elongation of plant roots in acid soils. We previously reported decrease in atomic ratio of potassium to phosphorus (K/P ratio) of dried root-tip of alfalfa (Medicago sativa L.) under Al stress using in-vacuum PIXE. In Via PIXE, 5 to 7-minute irradiation by 3 MeV proton beams of 200 pA was sufficient to obtain X-ray spectra without drying root samples. Decrease in K/P ratio in surface cells of root-tips was observed by short-term (6-8 h) exposure of root to Al. Via PIXE is recognized as a powerful tool for in-situ surface analysis of plant material.

A polycarbonate film of thin and uniform thickness was prepared. A casting solution for film-formation was made up by diluting a solution of poly (bisphenol A carbonate) in chloroform by a factor of two to three with benzene. A uniform film was created by dropping 0.2-0.3 cm³ of the casting solution slowly on a water surface within an aperture (20 mm diameter) of Mylar target frame floating on 50 wt% sucrose aqueous solution. Films of 0.14-0.27 mg/cm² thickness thus prepared offer a good combination of mechanical strength and low continuum backgrounds. To test PIXE analysis of anionic species in water, targets containing SO₄^2-, Cr₂O₇^2-, AsO₄^3-, and Ga³⁺-internal standard were prepared by depositing 100 μl of the test solutions onto the polycarbonate film, and irradiated in vacuum by 3 MeV proton beams. The difference between the nominal and the analyzed concentrations seldom exceeded ± 15 % in the range from 10 to 2000 ppb.