H.J. Maier

Preparation of radioactive targets for tandem accelerator experiments by high vacuum evaporation-condensation

Abstract Radioactive thin film targets have been prepared by high vacuum evaporation–condensation in the hot-lab facility of the University of Munich. Targets made by this technique are of high density and excellent smoothness, being well suited for experiments aimed at the production and spectroscopy of fission fragments. Cold crucible electron beam heating is the preferred method for evaporation of actinide isotopic material of sufficient abundance, for instance 230 Th, 232 Th, 233 U, 235 U, 238 U and 239 Pu. Exotic isotopes, which are available only in submilligram quantities, are processed in a micro-evaporator module consisting of a chimney-type crucible heated by low-tension electron bombardment. This set-up is characterised by a high collection efficiency and was used for the production of 244 Pu and 10 Be targets.

THE NEW HOT-LAB FACILITY FOR RADIOACTIVE TARGET PREPARATION AT THE UNIVERSITY OF MUNICH

Abstract The new hot-lab facility for the preparation of radioactive thin-film targets is almost completed and will be brought into service shortly. All the necessary equipment is integrated in a production line consisting of three glove boxes and a hot cell, which are interconnected by lock chambers. A complex health physics system serves to protect the laboratory staff as well as the environment from radiation damage and contamination. A status report and a survey of the target production concept will be given.

Preparation of 180Ta targets by high vacuum evaporation-condensation

Abstract A method for the routine preparation of enriched 180 Ta thin film targets by evaporation-condensation of submilligram quantities of Ta 2 O 5 onto thin C backings is described.

State of the art of high vacuum sputter deposition of nuclear accelerator targets

Abstract Experience using a high vacuum sputter deposition system over a two year period has shown it to be a reliable, economical way to prepare isotopically enriched targets. The present paper gives a survey of the many types of samples prepared so far and in some detail deals with the problem of impurities related to the procedure and their possible elimination.

Target development for the Munich fission fragment accelerator

The target for the Munich Fission Fragment Accelerator (MAFF) consists of typically 1 g of the fission material 235 U in the form of UC2; dispersed homogeneously in a cylindrical graphite matrix, which is encapsulated in a protective Re container. This special type of target is currently under development. The problems related to its manufacture are discussed. To enable diffusion and extraction of the fission products, the target has to be maintained at a temperature of up to 2700 K duringoperation. Extensive tests are required to study the long-term behaviour of the involved materials at these conditions. For this purpose a resistively heated high vacuum furnace has been set up, which allows hightemperature heat treatment of target samples for a period of up to 1000 h: r 2001 Published by Elsevier Science B.V. PACS: 28.41; 29.25.L; N; 29.27

Target conception for the Munich fission fragment accelerator

Abstract For the new high-flux reactor FRM II, the fission fragment accelerator MAFF is under design. MAFF will supply intense mass-separated radioactive ion beams of very neutron-rich nuclei with energies around the Coulomb barrier. A central part of this accelerator is the ion source with the fission target, which is operated at a neutron flux of 1.5×10 14 cm −2 s −1 . The target consists of typically 1 g of 235 U dispersed in a cylindrical graphite matrix, which is encapsulated in a Re container. To enable diffusion and extraction of the fission products, the target has to be maintained at a temperature of up to 2400°C during operation. It has to stand this temperature for at least one reactor cycle of 1250 h. Comprehensive tests are required to study the long-term behaviour of the involved materials at these conditions prior to operation in the reactor. The present paper gives details of the target conception and the projected tests.

Organisational and radiation protection concepts of the University of Munich hot-lab facility

Abstract The preparation of radioactive targets requires extensive precautions to protect laboratory staff as well as the environment from radiation damage and contamination. In the new hot-lab facility of the University of Munich, which is currently under construction, the technical equipment for target production will be integrated in a health physics system which meets these conditions in a very satisfactory way. Some details of the layout and the organisation of the laboratory will be given.

Optical filter for x-ray astronomy CCDs

Abstract Charge coupled device (CCD) detectors are sensitive from the X-ray to the NIR (near infrared) region. For X-ray and soft X-ray observations in astronomy, an optical filter has to be placed in front of the CCD to suppress the UV (ultraviolet) and VIS (visible) radiation of stars by more than 6 orders of magnitude. However, this filter must remain highly transparent at photon energies above 100 eV. A prototype filter was developed for a satellite borne CCD X-ray imaging detector. This unsupported filter has an effective size of 30 mm × 10 mm and is composed of multilayered thin films of parylene N, aluminum and carbon with mass densities of 25, 30 and 25 μg/cm2, respectively. The fabrication technique used for the filter and measurements of its optical and mechanical properties are presented.

Boron carbide as atomic oxygen protection for the Lexan-carbon filter on the ROSAT wide-field camera

The ROSAT Wide Field Camera, launched in June 1990, uses large area (50 cm2) thin film (typically 0.5 micrometers thick), band pass filters to select different extreme ultra violet wavelength bands. One of the filters consists of a substrate of the plastic polycarbonate, Lexan

Tracing and elimination of process-induced contaminations in sputter-deposited targets by elastic recoil detection analysis

DAG, interleaved with carbon and is thus susceptible to erosion by atomic oxygen in the ROSAT low earth orbit at 580 km altitude. The filter was protected against this erosion mechanism by using a thin overcoating of boron carbide. We describe the boron carbide coating process, the technique used to minimize the heat load on the fragile plastic foil, and the need for an additional adhesion layer of carbon. The chemical composition of the boron carbide as evaporated material on glass slides has been measured using several surface science techniques as well as by analysis of the soft x-ray and EUV transmission of sample foils and completed flight filters. Additionally, using ion and atomic oxygen sources, the effectiveness of the coating has been evaluated by laboratory measurements on sample foils.