Cross-sections for the elastic recoil of hydrogen isotopes for high energy helium ions

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Abstract

Cross-sections for the elastic recoil of hydrogen isotopes, including tritium, have been measured for 4He2+ ions in the energy range of 9.0–11.6 MeV. These cross-sections have been measured at a scattering angle of 30° in the laboratory frame. Cross-sections were measured by allowing a 4He2+ beam to fall incident on solid targets of ErH2, ErD2 and ErT2, each of 500 nm nominal thickness and known areal densities of H, D, T and Er. The uncertainty in each cross-section is estimated to be ±3.2%.

Introduction

Accurate knowledge of the concentration of hydrogen and its isotopes in materials is important in a wide range of applications. Ion beam analysis techniques have become common analytical methods for the determination of hydrogen and hydrogen isotopes in materials from trace concentrations to quantities constituting that of major constituent. Perhaps the most common IBA technique employed for hydrogen analysis is elastic recoil detection analysis or ERDA.

For samples containing multiple hydrogen isotopes it may be necessary to perform ERDA at energies exceeding that of the Rutherford threshold in order to achieve good mass resolution. It may also become necessary to employ high energy probing beams for the case of thick samples. In either case, accurate knowledge of the elastic scattering cross-sections for the incident beam interaction with the hydrogen isotope of interest is required. In a previous work from this laboratory we presented a technique for the high accuracy determination of H isotopes in materials [1]. In this work, we present cross-sections for the interaction of 4He2+ beams with each of the hydrogen isotopes in the energy range 9.0–11.6 MeV at a laboratory scattering angle of 30°.

Section snippets

Experimental method

The incident helium beams used in these cross-section measurements were provided by Sandia's 6 MV EN Tandem accelerator. Beam energy calibration was carried out using the 19F(p,γ) resonance at the proton energy of 0.827 MeV as well as the two resonance reactions 1H(19F3+,γ) and 1H(19F4+,γ) at the fluorine energy of 16.440 MeV. The average beam current on target during the cross-section measurements was ∼3 nano-Amperes. Two sets of tantalum slits define the beam profile on target. The first set

Results and discussion

Results for the individual cross-section measurements are presented in Fig. 2 and tabulated in Table 1, Table 2, Table 3. In Fig. 3, Fig. 4, Fig. 5 we present comparisons between our measured cross-section values and some of those available in the literature for the same scattering angle. Energy loss of the incident particle in the full hydride layer is calculated using SRIM2000 [3]. The average energy in the film is taken as the energy for which the cross-section applies.

Comparison between the

Conclusion

Forward elastic recoil cross-sections for 4He2+ interaction with each of the hydrogen isotopes have been measured over an energy range extending from 9.0 to 11.6 MeV and a laboratory scattering angle of 30°. For each case, a thin film composed of erbium dihydride was used as the target. Erbium dihydride holds an advantage over polymer targets in that the erbium hydride system, in the dihydride phase, is stable to temperatures up to 400 °C and is more resistant to beam induced loss of hydrogen.

Acknowledgements

The authors would like to thank Dan Buller for the operation of the accelerator and Carol LaDuca for the operation of the mass spectrometer during these experiments. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.

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Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.

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