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A method for the determination of the depth distribution of light elements in heavy materials is described. It involves the detection of light elements recoiling under the bombardment by a 35Cl beam. A resolution of 300 Å was achieved for the lithium present in a thin sample. The measures were done with layers of 1016 atoms/cm2 and it is estimated that quantities as small as 1014 atoms/cm2 can be located without much difficulty.

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Typed by Linda P. Rubin on CMC (JZ. J 068) * ABSTRACT: Over the last few years many ion beam techniques Lave been reported for the profiling of Vdrogen in materials. We have evaluated 9 of these using similar samples of hydrogen ion-implanted into silicon. When possible the samples were analysed using two or more techniques to confirm the ion-implanted accuracy. We report the results of this analysis which has produced a consensus profile of H in silicon which is useful as a calibration standard. The analytical techniques used have capabilities ranging from very high depth resolution (» SO Â) and high sensitivity (<1 ppm) to deep probes for hydrogen which can sample throughout thin sheets (up to 0.2 mm thick). There are eight basic approaches to hydrogen profiling with ion beams, with 14 variations.These are summarized in Table 1 and References 1-14. Each will be described in detail below.We report a round-robin comparative study of 9 of these techniques using identical samples of hydrogen implanted into silicon. Since several of the other ion beam techniqueswere not applicable to the target chosen for the round-robin, we include brief descriptions of these for completeness with mention of their particular advantages. SAMPLE PREPARATIONSilicon was chosen as the host material for this study for several reasons: '-*) it has extremely high purity with no known hydrogen incorporated into the bulk material, (b) it can be obtained with highly polished surfaces, (c) it is believed to trap ion-implanted hydrogen with high efficiency, and (d) silicon is a technologically important material. The hydrogen was ion-implanted into the silicon to provide reproducible hydrogen concentrations with sharp concentration gradients. These gradients provide a test of the depth resolution of the various techniques.The samples were made from Si <100> single crystals, 2.54 cm in diameter, with a surface chemically polished to better than 1 nm. 15 These wafers were etched in buffered HF, and then ion-implanted with Si at 270 keV, lxlO 15 Si/cm 2 , to make the surface amorphous We conclude that with proper concern for using accurate cross sections and stopping powers, and with proper identification of the sample surface, hydrogen can be profiled in Si with an absolute accuracy better than 8% up to depths of about 600 nm. Page 5 COMMENTS ON SPECIFIC TECHNIQUESThe typical experimental conditions for the analysis of H in Si are summarized in Table 2.Two items are of special comparative interest and are listed at the tyottom of the Figure 3 is a drawing of one type of experimental set up for hydrogen profiling using a nuclear reaction which produces a y-ray (this arrangement is described in detail in Ref. le).Two aspects are noteworthy:1. Two Nal(Tl) crystals were used to detect y-rays, with typical spectra shown in In order to convert this y-ray yield (Fig. 8)

Differential cross sections have been measured for the excitation, by 22.95-MeV protons, of states (up to and including the 6'^ at some angles) in the ground-state rotational bands of ^szrpj^ g^ĵ^j 238^ coupled-channel analyses of the angular distributions allow determination of the equilibrium deformation parameters P^^, The values Pi==0.017llfQll for ^^^U and i34 = 0.050± 0.015 for ^^^Th do not agree well with theoretical predictions by Moller et al.