International Journal of PIXE

Recent studies were reviewed on the PIXE analysis of metal ions preseparated by means of capillary type isotachophoresis (ITP-PIXE). The principle was described of isotacho-phoresis which was one of electrophoretic methods with high separability and concentration ability. Some applications of ITP-PIXE were demonstrated on the investigation of the separation behavior of metal ions and the analysis of trace elements in a crude rare earth chloride from a monazite and a model mixture of a high level liquid waste. It was revealed that PIXE could be a powerful detection method for the fractions of isotacho-phoresis because of its high sensitivity and multielemental analyzability. Since the matrix effect in X-ray measurement was significantly reduced by such preseparation, the minor elements could be determined accurately.

The yields of Kα x-ray production from the bombardment of metal targets with protons were measured in vacuum and in gaseous environment (external beam technique) for proton energies between 1.5 and 8 MeV. For the measurements in gaseous environment the influence of the secondary electrons (delta electrons) emitted from the gas, to the x-ray yields was investigated. For this purpose a suitable model was introduced and tested experimentally. Finally, the experimental K shell ionization and x-ray production cross sections were calculated for the same targets and compared with three theoretical and two semiempirical approximations.

Photon-induced L X-ray production cross sections have been calculated for even Z in the region Z=40–92 at different excitation energies. The results have been compared with the experimental values, and the effects of the choice of atomic parameters — like fluorescence yields, Coster-Kroning transition probabilities and relative emission rates — used in calculating L X-ray production cross sections have been discussed.

The PIXE system with a detective sensitivity of 10^–11g for elements was used to study the quantitative effects of the components of Murashige and Skoog (M&S) salts. Concentrations of 14 elements in Polygonum tenuicaule cultured in M&S medium with different modifications were analysed. The physiological function of M&S salts and such integral components as KH₂PO₄, FeSO₄, KNO₃ and CaCl₂ were disclosed. Some features of M&S medium and plant absorption mechanism are reported for the first time.

At E_p=40 MeV, protons have sufficient energy to overcome the coulomb barrier of most elements. The resultant interaction between protons and nucleii of many can produce radioactive isotopes via nuclear reactions. The decay schemes of isotopes created in this manner may include the emission X-rays and gamma-rays that can provide useful analytical information.

There is often a need to determine simultaneously both elements of an adjacent elemental pair whose K_α and K_β X-rays cannot be adequately resolved by the detector. The extent to which specific adjacent elements (viz. K-Ca and V-Cr) mutually interfered with each other was studied by PIXE on thick and thin targets specially prepared from synthetic mixtures. To monitor the lowest relative concentration for which significant results can be obtained, the concentration of each element in each of the pairs studied was systematically changed.

A misch metal, an alloy of light rare earth elements, was analyzed by a new coupled analytical method, ITP-PIXE(isotachophoresis—Particle Induced X-ray Emission) : The sample solution containing ca.1 mg misch metal was separated and fractionated by the use of a preparative isotacho-phoretic analyzer. The dropwise fractions containing nanomole rare earth elements were analyzed off-line by PIXE. The matrix effect in X-ray measurement was reduced by the isotachophoretic removing of the dominant lanthanoids and preconcentration of the trace elements of interest. Consequently the minor elements, Sm, Gd, Tb, Dy, Ho, Er, Yb and Y could be determined accurately. The most trace element found was Yb (4ppm, 4ng in 1mg sample). The good accuracy of ITP-PIXE method was also demonstrated for several model samples of lanthanoids, where La was the dominant element and the thirteen lanthanoids were the minor elements. The ratio was varied from 500:1 to 50000:1. Even in the case of 50000:1, ca. 10% accuracy was achieved for each minor element except for Sm(23%), Gd(17%) and Yb(18%). The analytical results by ITP-PIXE were compared with those by means of ICP-AES(Inductively Coupled Plasma—Atomic Emission Spectrometry).