TIPP 2011 - 2nd International Conference on Technology and Instrumentation in Particle Physics

Feasibility Study for an Active 238UF6 Gas Target for Photo-Fission Experiments

Not scheduled

1m

Sheraton Hotel (Chicago)

Poster Presentation Gaseous Detectors

Speaker

Mr Martin Freudenberger (Institut fuer Kernphysik, TU - Darmstadt, Germany)

Description

Nuclear fission represents a class of important reactions in heavy nuclei. Fission may occur spontaneously as well as induced by charged particles, neutrons or photons. A detailed microscopic description of the fission process is still lacking, whereas phenomenological parameterizations, e.g. fragment yield and total kinetic energy, have been realized. A program for studying photon-induced fission of actinide nuclei in the energy region of the fission barrier, has been started at the Darmstadt superconducting linear accelerator S-DALINAC. First experiments were performed using a twin Frisch-grid ionization chamber with a solid target located at the central cathode [1]. For detailed investigations on, e.g. the energy dependence of fission modes [2], the population of super- and hyper-deformed states, the so-called fission isomers, or even the search for parity non-conservation in fission [3], higher luminosities - and hence thicker targets - are needed. However, increasing target thickness reduces mass and angular resolutions. One solution to this problem is an active gas target. The gas of choice is 238UF6, because of its phase transition from solid to gas at 56,4 °C and atmospheric pressure via direct sublimation. In order to test 238UF6 as an admixture to standard counting gases (e.g. argon) and to study its properties, an ionization chamber was designed and built at the Institut für Kernphysik of Technische Universität Darmstadt. In a first step the chamber itself was tested with pure argon as counting gas, and the drift velocity as a function of the reduced electric field strength was determined. Then 238UF6 was filled into the chamber in steps of one mass-percent uranium for each measurement, where both signal quality and drift velocity at different admixtures were determined. Present results using mass fractions up to 2 percent of 238U in the counting gas show that the drift velocity increases with 238UF6 content, while overall a good signal quality and energy resolution of the ionization chamber is preserved. Supported in part by Deutsche Forschungsgemeinschaft through the SFB 634, by the State of Hesse through the LOEWE centre HIC for FAIR, and through the GSI-TU Darmstadt cooperation contract. [1] A. Göök, M. Chernykh, C. Eckardt, J. Enders, P. Von Neumann-Cosel, A.Oberstedt, S.Oberstedt, A.Richter, Nucl. Phys. A 851 (2011) 1. [2] U. Brosa, S. Grossman, A. Müller, Phys. Rep. 197 (1990) 167. [3] V. V. Flambaum and G.F. Gribakin Prog. Part. Nucl. Phys. 35 (1995) 423.