The scope of NDP can be expanded by measuring (via time-of-flight) the kinetic energies of the recoils emitted from (n,p) or (n,) reactions. When they occur inside a solid, the energies of the emerging recoils reveal depth from which they originated. The Recoil Nucleus Time-of-Flight NDP (RN-TOF-NDP) technique can reveal the depth distribution of some isotopes (e.g.,10B,210Bi) with a resolution of a few Å. Furthermore, it is possible to detect atomic and molecular species ejected at the surface site where the recoil emerges from the solid. This paper discusses the methodology for RN-TOF-NDP and its applications including surface analysis based on atomic and molecular ions codesorbed with the recoils.
The backscattering performance of 2 MeV He+ and N+ beams was studied using Ta2O5 targets as test targets. To allow ready comparison, the scattering geometry, projectile energy, and detection system were kept identical for both beams. Tantalum oxide films with thicknesses of 200 Å to 4000 Å were examined. For thickness determinations, beam straggling was found to be the major limiting factor. For thickness measurements below 1000 Å the N+ beam is best suited for larger thicknesses; the He+ beam is superior. For stoichiometric determinations both beams provide equally accurated and precise data.
This method is based upon the measurement of 3.95-hr43Sc which is formed during α-activation from40Ca, the most abundant (96.8%) isotope of calcium. The excitation function for the40Ca(α, p)43Sc reaction was determined and the maximum yield of43Sc (about 107 cpm per mg of calcium for a 1-hr irradiation at a beam current of 1 μA) was obtained at an irradiation energy of 14 MeV.
The interference free sensitivity of the method at this energy was found to be 8.5·10−12 g, for a 1-hr irradiation at a beam current of 10 μA. The elements most likely to interfere with the determination are potassium
and scandium. The extent of this interference was investigated as a function of irradiation energy and methods to eliminate
or subtract the activity formed from these elements are discussed. An attempt was made to determine non-destructively the
calcium content of very pure silicon and aluminium and upper limits for the concentration of calcium in these samples were
set at 0.27 ppb and 6.9 ppb, respectively. Magnesium, thulium oxide and yttrium oxide samples of known calcium content were
The capabilities of reactor neutron and 12 MeV proton activation were evaluted on samples of orchard leaves, beef liver and
bovine liver. Based on γ-ray spectrometry, As, Ca, Cu, Fe, Mo, Pb, Sr, Ti, Zn and Zr at levels ranging from 2 to 20 900 ppm
were detected following proton activation of 1 hour. Al, Br, Ca, Cl, Cu, Mg, Mn, Rb and V (ranging from 0.4 to 20 900 ppm)
were measured by neutron activation (1 min irradiation). As, Ba, Br, Cr, Co, Fe, Hg, La, Na, Rb, Sb and Zn (ranging from 0.2
to 2400 ppm) were determined following a 14 h neutron irradiation. Although covering different elements, the two techniques
are comparable in their scope, i. e. detection limits that can be achieved and number of elements that can be detected simultaneously.
Procedures for instrumental neutron activation analysis have been developed and used on flint samples collected from the Edwards
Formation in Texas. Each of the samples was analyzed for Mn, Ca, V, Al, Sc, Co, Fe, As, and K. USGS standard rocks AUG-1,
GSP-1, and G-2 were also analyzed in order to test the reliability of this technique. Means and standard deviations of each
element determined were calculated. The elemental values ranged from 0.03 ppm for scandium to 1500 ppm for aluminium. Based
on relative elemental abundances, the rocks could be classified into two types of flint. This information suggests elemental
inhomogeneity in the Edwards Formation.
A novel method for the characterization of metal containing biological compounds has been developed which utilizes both nuclear
activation [e.g.,12C(3He, α)11C] and atomic activations (X-ray emission) induced by 8 MeV3He bombardment. Detection limits for carbon (≈1 μg), oxygen (≈1μg), and metals (1 to 10 ng for elements between P and Zn)
were obtained under routine experimental conditions. The metal stoichiometry of six different compounds (alkaline phosphatase,
amylase, carbonic anhydrase, diamine oxidase, my oglobin, vitamin B12) were determined with typical relative precisions of ±25% for a 40 μg sample. A comparison of these ratios with carbon and
metal measurements obtained by other methods showed a relative accuracy of 1 to 20%.
A multitude of ion-atom interactions are induced with projectiles of E0.1 MeV/nucleon. Analytical techniques derived from these include particle induced X-ray emission (PIXE), charged particle activation analysis (CPAA), prompt nuclear reactions (PNR), and Rutherford backscattering spectrometry (RBS). Among their features are broad elemental coverage (PIXE), subnanogram sensitivity (PIXE, CPAA), isotopic specificity (CPAA, PNR), and depth resolution (RBS, PNR). A limiting requirement with each technique is the need for high intensity ion beams. Novel approaches seek now to obtain analytical information with very small numbers of bombarding ions. Sample integrity is then maintained; moreover, they can be delivered in a microbeam (diameter 5 mm). A phenomenon which under these conditions provides useful analytical information is the particle induced desorption of molecular fragments. Thus, microscopic chemical analysis can be achieved with a small number (<10,000) of heavy fast projectiles and identification of the species desorbed from the sample surface via time-of-flight mass spectrometry. Experimental work with 84 MeV kr ions indicates the following: (a) high desorption yields can be obtained (>50%); (b) mass spectrometry on microspots (diameter of a few m) is feasible; (c) < 106 atoms can be detected. Further capabilities of ion beams for minute, detailed, and comprehensive chemical characterization remain to be explored.
Among the numerous heavy ion reactions, those of potential interest for chemical analysis can be identified based on their
Q values, Coulomb barriers, and threshold energies. A simple computer code has been written for these calculations. The use
of the calculated data is illustrated with a survey of the possibilities of HIAA with N+, Li+, B+, Be+ and C+ beams yielding radioisotopes with half-lives of 10 to 104 sec.
Authors:M. Vargas, J. Batchelor, and E. Schweikert
The determination of lead via 30 MeV4He bombardment to produce the long-lived radioisotope210Po was studied. The validity of the technique was tested by the analysis of a series of NBS glass samples doped with 61 different trace elements at nominal 500 to 1 ppm level concentrations. The measurement sensitivity of alpha counting with surface barrier detectors was evaluated. The detection limit was estimated at 0.1 ppm. The4He-activation technique coupled with -counting features a unique combination of sensitivity and accuracy for the trace determination of lead.
9Be induced radioactivation was used to study the trace determination of 19 elements at 3 different ion beam energies (Elab=14, 32 and 63 MeV9Be2+). Nine nuclear reactions, yielding radionuclides with half-lives longer than 2.5 m, present potential analytical features. Beside the very sensitive detection of B and N, the multielemental determination of Na, Si, Ca, Sc, and Zn is possible with a9Be ion beam of appropriate incident energy. Nuclear interferences have also been investigated and quantified.