M. Buschmann

Hydrogen depth profiling using18O ions

Nuclear resonant reaction analysis techniques for hydrogen depth profiling in solid materials typically have used15N ion beams at 6.40 MeV and19F ion beams at 6.42 MeV, which require a tandem accelerator. We report a new technique using an18O ion beam at a resonance energy of 2.70 MeV, which requires only a single stage accelerator. Improved values of the nuclear parameters for the 2.70 MeV (18O) and 6.40 MeV (15N) resonances are reported. The beam energy spread was investigated for different ions and ion charge states and found to scale with the charge state. Data obtained using atomic and molecular gas targets reveal the research potential of Doppler spectroscopy. Examples of hydrogen depth profiling in solid materials using15N and18O ion beams are presented.

High energy resolution ion beam techniques for novel investigations in nuclear, atomic and applied physics using narrow nuclear resonances

Abstract The 400 kV accelerator at the Universitat Munster has been improved intense ion beams with high energy resolution. Gas and vapor targets required for high resolution experiments have been built. The energy scanning and data acquisition during the experiment was controlled by a computer. With this system an overall resolution of less than 25 eV for proton beams in the 100 μA range was achieved. The properties of this system are described. Using this system the width of nuclear resonances were determined to values as low as 3 eV. Such narrow resonances were also used as probes to investigate the influence of the nuclear environment on the yield curves. For example, replica resonances corresponding to atomic excitation of the electronic shells of the compound atom were observed, and a strong Lewis effect was measured for both solid and gas targets.

Atomic effects on α-α scattering to the 8Be ground state

The α-α scattering to the 8Be ground state was investigated in kinematic coincidence for the angle pairs 45‡/45‡ and 30‡/60‡ using the crossing beams technique, with an energy resolution of 26 eV. The nuclear resonance is split into 2 structures, not the 3 structures suggested by earlier work. The atomic physics origin of the splitting, the resonance parameters of the 8Be ground state, and astrophysical implications are discussed.

Influence of atomic excitation processes on yield curves of narrow nuclear resonances

Atomic excitation and ionization processes affect the shape of yield curves of narrow nuclear resonances obtained with high beam energy resolution. Yield curves for the narrow resonances in the 21Ne+p reaction at Ep=126, 272 and 291 keV and for the Ep=309 keV resonance in 23Na+p were measured with very low target densities (i.e., with thin targets fulfilling atomic single collision conditions). The ionization probabilities of K and L electron shells were determined at an impact parameter close to zero. Collision spectra were measured which provide information on the energy loss integrated over all impact parameters in a single collision. From an analytical description for the thin-target yield curve and the experimental collision spectra, the experimental thick-target yield curves with an intense Lewis peak could be reproduced with a Monte Carlo computer simulation.

Low energy resonances in21Ne(p,γ)22Na examined with a high energy resolution ion beam

TheER=126, 272 and 291 keV resonances in the21Ne(p, γ)22Na reaction have been investigated with a high-energy-resolution ion beam. TheER=272 keV resonance was found to consist of two states separated by (888+5) eV, where the lower (higher) energy member is a high-spin (low-spin) state. All four resonances have widths less than a few eV, which is an improvement of nearly two orders of magnitude below previously reported limits. The influence of atomic effects on the determination of the correct value for the resonance energy is examined.

Measurement and analysis of thin- and thick-target yield curves of narrow resonances with a high energy resolution ion beam☆

Abstract The 400 kV accelerator at Munster has been optimized with respect to high energy resolution and stability. Yield curves of narrow resonances in 21 Ne(p, γ) 22 Na have been investigated utilizing a windowless gas target of monolayer thickness (or less). The thermal Doppler broadening was the major contribution to the width of thin-target yield curves and was reduced by cooling the 21 Ne target gas to temperatures as low as 25 K. Atomic effects on the shape of thin- and thick-target yield curves are discussed.

Computer controlled ion beam energy scanning and data acquisition system and investigations of the Lewis effect

Abstract For high resolution studies of narrow (p, γ) resonances a computer controlled energy scanning system was developed at the 400 kV Munster accelerator. The system, targetry and results of Lewis effect studies are described.

A new UHV setup for investigations of narrow nuclear resonances with high energy resolution ion beams

Abstract A cryogenic target system has been built to study yield curves of narrow nuclear resonances. The crucial part of the UHV set-up is a liquid helium cooled sample holder mounted on a goniometer, allowing the use of gas and solid targets in the temperature range 10–600 K. Particle detectors and γ-ray detectors can be installed in close geometry to the target to achieve large solid angles. With this target system nuclear resonances in 21Ne(p, γ)22Na and 18O(p, α)15N have been investigated with high ion beam energy resolution. Effects of electronic excitation processes are clearly visible in the shape of yield curves of the 272 keV resonance in 21Ne(p, γ)22Na obtained at a temperature of ≈ 12 K. The width of the 151 keV resonance in 18O(p, α)15N was measured, where the data are significantly influenced by interference effects.

Novel applications of high-energy resolution ion beams

Abstract Improvements in targetry and ion beam energy resolution permit the observation of novel effects using narrow nuclear resonances as a probe. For the 400 kV Munster accelerator the ion-beam energy resolution was reduced to 15–20 eV at full ion-beam current. The development of UHV, vapor, and gas target systems allowed the use of very clean targets with variable density and temperature. With the energy spread of the ion beam approaching the eV level, the dynamics of the nuclear environment (atomic shells and solid material) become observable. Some novel applications in nuclear, atomic, molecular, and solid state physics are discussed.

VIBRATIONS OF SURFACE ATOMS STUDIED BY NRRA

The motion of the target nuclei in the surface of a solid affects the shape of yield curves of narrow nuclear resonances. We measured yield curves for the 272 keV resonance in 21Ne(p,γ)22Na with frozen neon. The in-situ preparation of the targets and the measurements were carried out under UHV conditions. The targets were cooled by a He evaporation cryostat to temperatures below 10 K. This temperature could be maintained even with beam currents of about 1 μA. The measurements were carried out with the 400 kV high energy resolution accelerator at the University of Munster. The measured yield curves showed a huge Lewis peak with a peak-to-plateau ratio of 2.5. The influence of atomic motion on the width of the Lewis peak was calculated with two different theoretical models. The calculated values are in good agreement with the experimental width.