C.J. Maggiore

A test of the smoothness of the elemental abundances of carbonaceous chondrites

The identification of CI chondrite concentrations with average solar system abundances for heavy elements is based primarily on the smoothness of the CI abundance curves for odd mass nuclei. A good test of smoothness is measurement of all elements in a given mass range in the same sample with the same technique. High precision proton-induced X-ray spectra of CI chondrites yielded analyses of 17 elements (Ni through Ru, plus Fe and Pb) with precisions better than 10% for all except As, Pb, Nb, and Ru. Excellent theoretical descriptions of the spectra were obtained. Two independent estimates of precision agree well, giving confidence in the quoted errors. Intersample differences are the largest source of variability. Within these limits good agreement with literature results are obtained, except for As and Y. Although our Y values are 10 to 30% lower than previously adopted, amonoelemental s-process peak in the abundance curve at Y is still necessary. Except for Br (higher by 59% in Ivuna), there are no significant concentration differences between Orgueil and Ivuna. In general, our results confirm previous abundance curves. The abundances are exceptionally smooth and strongly decreasing in the mass 60–75 region. From mass 75–101 a smooth curve can be drawn, within limits of intersample variability, except for the Y peak. Over the whole periodic table a large number of peaks of probable nucleosynthetic origin can be identified, some understood, some not. These smoothness deviations are 10 to 30% and set an overall limit to the smoothness argument alone in justifying using CI abundances as average solar system values.

FT-ICR with laser ablation and AMS combined with X-ray detection, applied to the measurement of long-lived radionuclides from fission or activation: preliminary results

Abstract The measurement of long-lived radionuclides from fission or activation is difficult when isobars are present. Preliminary results are reported here on two methods that can solve the problem in some instances. The first one, FT-ICR with laser ablation, has a very high mass resolution; the second one, AMS combined with X-ray detection, discriminates isobars using characteristic projectile X-rays (“inverse PIXE”).

Application of AMS and inverse PIXE to the study of radioactive waste management problems

Abstract Some long-lived radionuclides ( 59 Ni, 93 Zr, 93 Mo, 94 Nb, 99 Tc, 107 Pd, 151 Sm) must be measured at levels −3 Bq/g in radioactive wastes. No method is able to achieve this at the moment, except accelerator mass spectrometry (AMS) in the case of 59 Ni, using high energies. In this paper, we show that AMS at low energy (with a 3 MV tandem) is in principle able to measure the radionuclides of interest with the required sensitivity. To overcome the isobaric interferences, which are the limiting factor in AMS, characteristic projectile X-rays are measured (“inverse PIXE”).

High precision thick target PIXE analyses of carbonaceous meteorites

High precision proton-induced X-ray (PIXE) thick target spectra of carbonaceous meteorites have been deconvoluted using previously described programs. Even in cases of totally overlapping peaks excellent fits to spectra were obtained. Concentrations for 15 elements in the mass range 56–100, as well as Pb, agree well in most cases with previous literature values. The total concentration range studied was over 105, with the lowest concentrations precisely analyzed being around 1 ppm.

In situ ion-beam analysis and modification of sol-gel zirconia thin films

We report the investigation of ion-beam-induced densification of sol-gel zirconia thin films via in situ ion backscattering spectrometry. We have irradiated three regions of a sample with neon, argon, and krypton ions. For each ion species, a series of irradiation and analysis steps were performed using an interconnected 3 MV tandem accelerator. The technique offers the advantages of minimizing the variation of experimental parameters and sequentially monitoring the densification phenomenon with increasing ion dose.

Channeling and microactivation of materials

Abstract Charged particle activation analysis can be combined with channeling to determine lattice location of impurities at the trace level in single crystal samples. It can also be used with a nuclear microprobe to measure impurities at trace levels in small or spatially inhomogeneous samples. Examples of these extensions of activation analysis to realistic samples are carbon determination in organometallic vapor phase epitaxial layers of GaAlAs and GaAs and oxygen determination in diamonds.

Trace element contents of primitive meteorites; A test of solar system abundance smoothness

Elemental abundances from Cl carbonaceous chondrite meteorites are thought to represent the average solar system (“cosmic”) composition, based on the agreement between Cl and solar photospheric abundances and on the smoothness of heavy element abundances of odd mass nuclei when plotted as a function of mass number. To test Cl elemental smoothness, we have analyzed Cl meteorites, using conventional PIXE (proton probe) techniques, where we have good sensitivity for the range of elements: Ni to Mo. Preliminary analyses indicate that elemental smoothness is only approximate, with possible deviations of 30% to perhaps even 50%. This may be due to chemical fractionation. Alternatively, explanations for nonsmooth behavior may be understandable with the aid of general ideas of n-capture nucleosynthesis. As Cl abundances are refined, it could be that the lack of elemental smoothness may provide the strongest argument for the identification of Cl with primordial solar system abundances.

A review of high energy backscattering spectrometry

The technique and application of high-energy backscattering (HEBS) is reviewed in this paper. The advantages and limitations of the technique are discussed as well as the origins of the resonances in the cross sections which are fundamental for its application. Methods for determining the cross sections are presented including the fabrication of targets for measuring the cross sections. Applications for both α and proton HEBS are presented.

Direct and indirect measurements of hydrogen

Abstract We have demonstrated that the content of hydrogen in carbon-based films can be reliably calculated from a measurement made either directly using forward recoiled hydrogen or indirectly using backscattered helium. The method makes use of the surface signal height ratio of a sample of unknown composition to a standard of known composition. This approach allows elimination of several experimental parameters. The method assumes validity of Braggs rule, potential deviations from which account for the majority of the absolute uncertainty in the hydrogen fraction. In general however, we have found agreement in hydrogen content between the two techniques for several carbon-based films.

Interpretation of ion channeling results from epitaxial Pt thin films and CoPt multilayers

Abstract Ion channeling was used to characterize the orientation and crystalline quality of very thin ( Co >Pt multilayers grown epitaxially on (0 0 1) MgO single crystal substrates by electron beam evaporation. Planar channeling measurements were found to be particularly useful for characterizing the film orientation, and for identifying the structure of ultra-thin Co layers in the multilayers. Comparison of ion channeling and transmission electron microscopy (TEM) results points out several potential difficulties in interpreting ion channeling data in these highly mismatched epitaxial systems.