M. Berheide

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.

Gamma-ray detection with a 4π NaI spectrometer for material analysis

Abstract A γ-ray detection system with nearly 4π geometry for applications in materials science is described. The energy resolution of the NaI(Tl)-bore hole detector was found to be about 2% for 10 MeV γ-rays. The total detection efficiency has been determined to be above 80% for γ-energies between 0.5 and 20 MeV. A precision of the efficiency calibration of about 2% has been obtained for a wide range of γ-energies. The experimental results were found to be in excellent agreement with computer simulations using the GEANT computer code. The high efficiency of the system combined with its relatively high energy resolution opened a wide range of applications. Examples are the simultaneous detection of light isotopes in thin films by (d,pγ) nuclear reactions, high depth resolution profiling of isotopes by narrow, low-energy resonances in (p,γ) reactions, and hydrogen profiling using the 6.4 MeV resonance in the 1H(15N,αγ)12C reaction.

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.

Search for the 70 keV resonance in17O(p, ?)14N

A direct search for theER=70 keV resonance in17O(p, α)14N was carried out using17O enriched Ta2O5 targets in combination with a 1 mA proton beam and suitable detectors of large solid angle. The observed upper limit for the resonance strength isωγ≤8×10−10 eV.

Efficient γ-ray detection in ion beam analysis☆

Abstract A γ-ray detection system of nearly 100% efficiency is described allowing analytical techniques such as nuclear reaction analysis (NRA), nuclear resonance reaction analysis (NRRA) and deuteron induced γ-ray emission (DIGME) to be performed with a minimum of beam induced sample damage. Using this system together with ion beams of low energy spread and narrow resonances at sub-Coulomb energies, NRRA can be performed with a depth resolution of about 1 nm in the surface region of a sample. The energy scanning of the accelerator and the data acquisition are performed by a computer controlled system.

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.

Concept and status of the new sample preparation and analyzing facility at Bochum

Abstract The technical conditions of the activities at the Dynamitron Tandem Accelerator Laboratory at Bochum in the field of ion beam modification and analysis of thin films will be improved. A new 500 kV accelerator with high energy resolution of the ion beams as well as a UHV system consisting of several chambers are presently being built up. The beam lines of the new accelerator and of the 4 MV Tandem are interconnected, providing a wide range of ion species and energies at the target sites. The UHV system not only allows the use of ion beam techniques but also provides standard electron spectroscopic techniques for surface analyses. For sample preparation techniques such as standard furnace evaporation, electron gun evaporation and rapid thermal processing are available.