R.W. Ostendorf

Development and Characterization of Large La-Halide Gamma-Ray Scintillators for Future Planetary Missions

Future planetary missions such as BepiColombo are resource limited in both mass and power. Due to the proximity of the spacecraft to the Sun, the instrumentation will encounter harsh environments as far as radiation levels and thermal loads are concerned. Only radiation hard detectors that need little or no cooling will be able to successfully operate after long cruise times and over the expected mission lifetimes. The next generation of lanthanum halide scintillators promises to provide sufficient resolution in the spectral range between 1 and 10 MeV where most of the elemental gamma-ray emission lines can be detected. In order to be suitable for planetary gamma-ray spectrometers with sufficient sensitivity it had to be proven that larger crystals of size 3 can be produced and that they maintain their resolution of 3% at 662 keV. For that purpose we have produced and characterized several larger crystals and assessed their radiation hardness by exposing the crystals to radiation doses that are representative of the expected conditions in the space environment. Systematic measurements on several crystals allowed the determination of the activation potential and the performance verification from which the consequences for instrument flight performance can be derived. From these investigations we conclude that these scintillators are well suited for planetary missions, with excellent and stable performance.

HINDAS A European Nuclear Data Program for Accelerator-Driven Systems

In the HINDAS program, nuclear data in the 20-2000 MeV range are evaluated by means of a combination of nuclear tmodels and well-selected intermediate- and high-energy experiments. A panoply of European accelerators is utilized to provide complete sets of experimental data for iron, lead and uranium over a large energy range. Nuclear model codes are being improved and validated against these new experimental data. This should result in enhanced ENDF-formatted data libraries up to 200 MeV, and cross sections for high-energy transport codes above 200 MeV. The impact of the new data libraries and high-energy models will be directly tested on some important parameters of an accelerator-driven system (ADS). Here, we report the recent progress of the various experimental and theoretical activities in HINDAS.

Identification of photons and particles in the segmented electromagnetic calorimeter TAPS

Abstract The algorithms devellped for the identification of one and two hard-photon events detected with TAPS are presented. After a presentation of the energy and time calibrations, the identification of single module events and the shower reconstruction, special emphasis is given to the rejection of the background generated by cosmic rays, π 0 decay and e ± conversion pairs. The effect of discontinuous showers is also discussed. The method was tested on data taken with TAPS at GANIL for heavy-ion collisions at energies of several tens of A MeV.

AGORFIRM, the AGOR facility for irradiations of materials

AGORFIRM is an activity of the KVI, a cyclotron laboratory in the Northern part of the Netherlands. Central in the institute is the superconducting cyclotron AGOR. AGORFIRM is a facility that uses a dedicated beam line of the AGOR cyclotron for irradiations with protons and carbon ions in air. The facility is on a regular basis available for radiation damage and radiobiology studies. This paper gives an overview of the facility, the various beams and services available and of recently conducted characterization measurements and modeling.

Effect of prolonged annealing on the performance of coaxial Ge gamma-ray detectors

The effects of prolonged annealing at elevated temperatures have been investigated in a 53cm3 closed-end coaxial high purity germanium detector in the reverse electrode configuration. The detector was multiply annealed at 100°C in block periods of 7 days. After each anneal cycle it was cooled to 77 K and the relative efficiency, peak channel location and FWHM energy resolution measured at 6 gamma-ray energies. At the present time, the detector has completed 16 anneal cycles. It was found that above ~ 662 keV the photopeak efficiency decreased almost linearly at a rate of ~ 1.5% per anneal cycle, although the energy resolution and centroid (and therefore charge collection efficiency) remained unchanged. The change in detection efficiency is attributed to the expansion of the inner n+ contact due to the thermal drive-in of Li ions into the bulk. The rate is found to follow a power-law dependence in agreement with that expected from Ficks diffusion laws. Using these data, we have derived a simple 1-D phenomenological model in which the n+ contact thickness is simply related to the Li diffusion length. For annealing at 100°C, the thickness of the n+ contact, d, as a function of the annealing time, t, can be described semi-empirically by d(mm) = 0.231 × t(days)1/2.

Measurements of the virtual bremsstrahlung yields in the p+p system

Abstract In this paper recent results obtained from the p + p → p + p + e + + e − experiment are presented. This experiment has been performed with a 190 MeV polarized proton beam obtained from the new cyclotron AGOR at KVI in Groningen. Differential cross sections have been obtained in exclusive measurements in which all four exit particles have been measured in a coincidence setup between SALAD and TAPS. The data are compared with LET calculations. A reasonable agreement is found for virtual-photon invariant masses up to 80 MeV/c 2 .

Separation of proton-induced fission isotopes from dominant evaporation residues by adapted target stacking

Abstract To study low yields of fission products from proton-induced reactions we introduce two activation methods based on target stacking with suppression of otherwise dominating evaporation and spallation products; one method using thin Mylar foils which only transmit the fission products, the other one using cylindrical catchers at both sides of the target foils. The methods require no radiochemistry. Tests have been performed with targets of decreasing atomic number and decreasing fission cross-sections.