A.E. Pillay

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.

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.

PIXE yield enhancement of metal fluorides under bombardment with charged particles

The abnormally high yields of X-rays from metal fluorides were considered to be charge related or due to the prompt gamma rays from the decay of coulomb excitation of the19F nucleus. A detailed study with singly and doubly charged helium-3 ions confirmed the exceptionally high enhancement of the metal X-rays from the fluorides, but the mechanism favoured a discharge process from charge build-up in the insulating targets.

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.

Charge-induced X-ray yields from some metal salts with proton and alpha beams

Previous studies reporting abnormally high X-ray yields from the fluorides of some transition metals were extended to include a variety of other compounds. Using proton beams of 700 and 2000 keV and α-beams of 1000 keV the production of abnormally high X-ray yields were critically examined for reproducibility and under different vaccum and bombarding beam conditions.

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.

Charge-induced X-ray spectrometry with deuterons and alpha-particles in the energy range 700-2000 keV

Introductory work with deuterons and α-particles provided information to confirm increased yields obtained in Charge Induced X-ray (CHIX) studies. This extension of earlier work includes a detailed study on some thick targets irradiated with2H+ and4He+ ions at beam energies in the range 700 to 2000 keV. Some factors affecting the increased X-ray yields are discussed.

The measurement of “enhanced” L and M X-ray yields from charge-induced studies with protons and1H 2+ ion beams

Earlier work on Charge Induced X-rays (CHIX) was extended to include the X-ray energy region between 0.70 to 4.0 keV. Protons of 700 keV, and1H2+ ion beams of equivalent proton energies in the range 350–450 keV were used to produce “enhanced” yields of L and MX-rays from a suitable selection of highly compacted non-conducting samples. “Enhancement” factors are given and possible applications are mentioned.

Some studies on nuclear methods for boron determination

Abstract A summary of some studies of nuclear methods for the low-level determination of boron is presented. Since there is always need for an interference-free method, the study provides an impartial insight into the relative analytical capabilities of the methods of interest following intensive investigations in this area over prolonged periods. Of particular interest is the role played by interfering components such as carbon, nitrogen and oxygen which are invaribaly present in major concentrations in most sample matrices. A critical evaluation of the analytical potential of prompt, delayed and coincidence procedures is provided with emphasis on selective activation for boron in the presence of major interferences. Some future possibilities are proposed, and typical applications of the relevant methods for operation under routine conditions are discussed.