M. Peisach

Enhanced X-ray yields in PIXE analysis of some binary metal fluorides

Abstract Enhanced X-ray yields from the metal components of homogeneous thick targets of binary metal fluorides were observed during PIXE irradiations with protons, deuterons and 3He ions. The absence of these effects in the pure metals and in the corresponding metal oxides, nitrides and borides suggests that the fluoride component in such compounds plays a key role in producing the enhancement. Coulomb excitation of the extremely low-lying levels of the fluorine nucleus is discussed as a possible mechanism for the improved yields via secondary excitation.

A PIXE study of abnormal X-rays from binary fluorides with protons in the range 0.4–2 MeV

Previously reported abnormally high X-ray yields from the fluorides of some transition metals were confirmed. Using proton beams and beams of the molecule-ion 1H2+, at equivalent proton energies between 400 and 2000 keV the conditions for the production of abnormally high X-ray yields were studied for the effect of ion beam energy, beam current, charge, target thickness and atomic number of the target metal. The effect was probably due to buildup of potential and discharge with the production of a flux of energetic electrons, with an energy distribution peaking above 10 keV.

Ion beam analysis for the determination of cation ratios as a means of dating Southern African rock varnishes

Abstract Stone artefacts found on the surface over much of the arid areas of Southern Africa are often covered with a rock varnish, the trace element composition of which has been analyzed by particle-induced X-ray emission (PIXE) and particle-induced gamma-ray emission (PIGME). Because Ti deposited in the varnish is less soluble and mobile, substitution of alkali metals by Ti served as a basis for dating. An experimental relationship was established between the “cation ratio” and the age of artefacts dated by more conventional means. This relationship provides a cation leaching curve from which undated samples can be dated by their cation ratios.

The measurement of enhanced PIXE yields with 3He2+ ions

Abstract The cause of the high enhancement factor in a PIXE study of metal fluorides was investigated with singly and doubly charged 3 He ions. A comparison of the X-ray yields and enhancement factors showed that gamma rays from the de-excitation of coulomb excited 19 F ions were not responsible for this effect. Charge buildup and subsequent discharge produced energetic electrons which generated the large yields of X-rays. The energy distribution of these electrons ranged from a low concentration at energies around 4 keV, peaked at an energy around 10 keV and extended to beyond 30 keV. The importance for PIXE analysis was noted.

Cation-ratio differences in rock patina on hornfels and chalcedony using thick target PIXE

Abstract The ratio of (K + Ca) to Ti in patina layers is time-dependent and decreases with age. Patinas on hornfels and chalcedony artefacts were irradiated by 2 MeV 4He+ ions and analysed by Rutherford backscattering and PIXE simultaneously. The patinas on hornfels and basalt showed a self-consistent variation of cation-ratio with typological age up to 128000 years B.P., but the rate of growth was apparently slower on chalcedony.

Micro-analysis of kidney stones sequentially excreted from a single patient

Abstract Eight kidney stones obtained from a single patient over a period of about eleven years were analysed in its natural form by Rutherford backscattering with 2 MeV 4 He + ions, PIXE with 3 MeV protons, and PIGE with 4.5 MeV protons using the newly installed nuclear microprobe at Faure. Since the mechanism of kidney stone nucleation and growth is still poorly understood, it was of interest to establish whether kidney stones from a single patient were constant in composition as regards trace element content and whether the type of stone is reproduced on new stones grown after the removal of existing stones. As expected, the stones were rich in Ca. The matrix was calcium oxalate. Light elements present in minor concentrations were P, S, Cl and K. Trace elements were in very low concentrations, and the presence of Fe, Ni, Cu, Zn, Se, Br, Rb, Sr and Pb were recorded. Trace element trends in the stones, analysed with micro beams were identified. A good positive correlation between Sr and Zn was observed.

Determining the origin of 18th and 19th century pottery and glasses using PIXE and PIPPS

Abstract Data on the concentrations of K, Ca, Ti. Mn, Fe, Cu, Zn, As, Rb, Sr, Zr, and Pb were obtained by PIXE and Li, Na, Mg, Al, Si, and Ca were obtained simultaneously by PIPPS in the analysis of pottery and glass using the external beam technique. Multivariate statistical methods of correpondence analysis were used to classify the specimens into groups of local and foreign origin. Possible sources of some intact objects of unknown origin were indicated.

Time variation of abnormal PIXE yields from some insulating binary metal fluorides under proton bombardment

Abstract Time-resolved multiscaler measurements were used to observe periodic increases in X-ray yields as a result of the discharge of the built-up charge in insulating targets of FeF 3 , CoF 2 CuF 2 · 2H 2 O and ZnF 2 bombarded with 1 nA of 1.5 Me V protons.

Thick target PIXE analysis of coastal and inland Namibian pottery

Abstract Suites of potsherds from herder coastal and inland sites were analysed by PIXE with 3 MeV protons. Correspondence analysis was carried out using the 12 elements that were common to most samples. The coastal suite was more heterogeneous than the inland one and reflected a greater mobility of their material culture. Thick target methodology was used to evaluate the concentrations of trace elements.

Application of “abnormal” X-ray yields from primary targets of compounds in XSQR studies with proton and alpha particle beams

Previous reports on “abnormal” yields from charge induced X-ray studies (CHIX) have demonstrated conclusively that such yields are exceptionally high when compared to PIXE at low incident particle energies. A combination of low incident energies and high X-ray yields could be useful for XSQR investigations with low energy accelerators, particularly in studies where the sample matrix “swamps” the signals from the impurities of interest such as chromium in steels (overwhelming Fe peak) and Cu in brass (high Zn peak). This work discusses the possible applications of CHIX to XSQR studies with primary targets of compressed powders of selected compounds under bombardment with 3000 keV alphas and 800 and 1000 keV protons. A feature of interest in the use of comparatively low beam currents (between 100–150 nA) in the absence of sample cooling. The advantages and limitations of the application are discussed.