Oxide fiber targets at ISOLDE

Abstract

Many elements are rapidly released from oxide matrices. Some oxide powder targets show a fast sintering, thus losing their favorable release characteristics. Loosely packed oxide fiber targets are less critical since they may maintain their open structure even when starting to fuse together at some contact points. The experience with various oxide fiber targets (titania, zirconia, ceria and thoria) used in the last years at ISOLDE is reviewed. For short-lived isotopes of Cu, Ga and Xe the zirconia and ceria targets respectively provided significantly higher yields than any other target (metal foils, oxide powders, etc.) tested before. Titania fibers, which were not commercially available, were produced in a relic process by impregnation of a rayon felt in a titanium chloride solution and subsequent calcination by heating the dried felt in air. Thoria fibers were obtained either by the same process or by burning commercial gas lantern mantle cloth. In the future a beryllia fiber target could be used to produce very intense 6 He beams (order of 10 13 ions per s) via the 9 Be(n,α) reaction using spallation neutrons.(Submitted to Nuclear Instruments and Methods in Physics Research B) Introduction A great variety of materials is used as ISOL (isotope separation on-line) targets (see e.g. [1]): molten metals, solid metals (as foils or powder), carbides, oxides and other compounds. Here we will discuss recent on-line results (release parameters and yields) of ISOLDE oxide targets and, in particular, of oxide fiber targets.Oxide targets have a long history at ISOL facilities. Already in the very first ISOL experiment [2] a 10 kg UO 2 target was used. Then, in the first experiments at ISOLDE several oxide targets served to produce radioactive noble gas isotopes [3,4]. These oxides (TiO 2 , ZrO 2 , CeO 2 and ThO 2 ) were precipitated out of solutions, vacuum-dried at room temperature and ground to powder. The targets were only partly dehydrated when operated at room temperature and had average delay times (for Kr and Xe) of 17 − 110 s [5].Later, other oxides were used at higher temperatures, after having been dehydrated by slowly heating them off-line under vacuum. All these oxides were used in form of powder or as pills of pressed powder: BeO, MgO, Al 2 O 3 , CaO, SrO, BaO, La 2 O 3 , ThO 2 and UO 2 . However, a powder target has a large number of mutual contact points between the individual grains. When heated for longer time to high temperature, the grains can "bake together" at these contact points and the formerly fine-grained powder will sinter to a bigger block with consequently longer diffusion paths and slower release. This was observed in particular for thoria and urania powder targets. Here it would be preferable to use instead thin fibers, which are arranged as a loose "pile of spaghetti". They have less mutual contact points and provide a better mechanical stability even when sintering starts locally at the contact points.Felts and cloths made from fibers of ZrO 2 and other oxides are commercially av...

Measurement of theβ-asymmetry parameter ofCu67in search for tensor-type currents in the weak interaction

“…Both isotopes were produced at ISOLDE (CERN) with a 1.4 GeV proton beam from the Proton Synchrotron Booster bombarding a ZrO 2 felt target (6.3 g Zr/cm 2 ) [26] connected to RILIS [27,28], which provided the required element selectivity. After ionization and acceleration to 60 keV, the ion beams were massseparated by the General Purpose Separator, transported through the beam distribution system, and implanted into a polished and annealed 99.99% pure Fe foil (size 13.1 mm × 15.5 mm, original thickness 250 µm) soldered onto the cold finger of the NICOLE 3 He-4 He dilution refrigerator [29,30].…”

Nuclear magnetic moment ofAs69from on-line β-NMR on oriented nuclei

“…A 1.4-GeV pulsed proton beam (3 × 10 13 protons per pulse) from the CERN Proton Synchrotron Booster accelerator (PS Booster) was used to produce the 69 As nuclei by spallation * Electronic address: nathal.severijns@fys.kuleuven.ac.be in a 11 g/cm 2 ZrO 2 fiber target [9]. The reaction products diffused out of the 1900 • C hot target and effused via a hot transfer line to a FEBIAD-type "hot plasma" ion source.…”

“…Then, two more detailed scans with frequency steps of 1 MHz, with a 1.1-MHz modulation amplitude and a 100-Hz modulation frequency, were performed in the region from 175 to 165 MHz. All six scans were least-squares fitted simultaneously, allowing for a nonzero spin-lattice relaxation time T 1 , yielding ν res = 169.98 (9)MHz (8) and…”

An off-line method to characterize the fission product release from uranium carbide-target prototypes developed for SPIRAL2 project

“…Recently, UC x -coated fiber targets were developed as RIB target materials [36][37][38]. It has been shown that fibers, arranged as a loose network, have few mutual contact points and could provide more permeability and mechanical stability for the target [39]. Moreover, because of their good thermal stability in vacuum (up to 2200°C in absence of oxygen [40]), these fibers are expected to play the role of grain growth inhibitor thus preventing the pores from collapsing at high temperature.…”