1. http://www.cern.ch/RIBO http://www.cern.ch/RIBO Mario.Santana@cern.ch References Introduction to the Radioactive Ion Beam Optimiser: RIBO Applications to EURISOL and SPES Mario Santana Leitner MAXIMIZATION OF RIB EXTRACTION New facilities aim at more intense RIB’s. Most of the effort is put to increase the generation with bigger targets and powerful primary beams I(Y). However, large targets may entail long diffusion, effusion and sticking times, and thus, the most exotic isotopes may decay before extraction; the extraction efficiency (ε r ) is hindered. The Monte Carlo code RIBO [1] integrates all phenomena linked to extraction, for its prediction + optimization. EFFUSION. Individual trajectories are simulated for molecular and quasi-molecular flows. Collisions usually follow the cosine law [4]. These are the features of the effusion module: Unlimited full 3-D combinatorial geometry. Multiple source features. Adsorption in walls. Absorption in walls (transmission studies). Collisions with residual gas (hard-sphere) model. Several collision modes (Snell, Lambert, Isotropic) Computation of impedances. Time-share analysis. Moving walls (valves): New studies underway. Effusion through crystals [5] (semi-classic phonon theory). Random walk in Ta-129 target Scheme input file MK7 Diffusion release profile x,t for a non- homogeneous starting concentration IONIZATION & ION TRANSPORT RIBO tracks effusion up to and including ionization. Plasma Ionization probability p I : The cross section σ is read from “plION.dat”; t r is the effusion time in the ion source. Surface Ionization [6]: The different parameters are stored in “sion.dat”, “workf.dat” Transport of ions (k=q·dt/m): RIBO computes the trajectory of ions with B{x,y,z}, E{x,y,z} and {x,y,z} 0, {v x,v y,v z } 0 Recombination and emittance computations also included. MORE ABOUT RIBO (www.cern.ch/ribo) 1.Scripts: “3D-RIBO” exports geometry to POVRAY [7] ray tracer. “Trace” plots (through PAW) individual trajectories. 2.Output post-processing: Direct fit of test effusion release functions to statistical momenta,, …, of results. Computation of Release Fraction for a grid of values {T 1/2, t sticking, D iffusion } through Laplace transforms. APPLICATION TO THE UC DISCS TAR- GET FOR THE SPES PROJECT AT LNL Features 1-6 of RIBO are used in series with MCNPX to estimate the production of n-rich radioisotopes in the SPES-RIB project at INFN. Simulations concern the “multi-thin” target [8,9], with 7 UC 6-cm diameter pills. The preliminary results yield these release fractions (RF): Remarks: The reference diffusion time constant is 9 s [1] table A.6 2.3 % of the effusion time spent in each pill. Average free flight = 160 m 10 5 collisions in the powder, i.e. 95% of total. SPES target (7pills +5 dumps) design view and RIBO input file view, the latter produced with RIBORAY DRF is the diffusion release fraction. 3 Different time diffusion time constants and 3 different sticking times have been tested for 6 half-lifes. Mass was A=95, and = 15 micrometer. [1] M. Santana Leitner, A Monte Carlo Code to Optimize the Production of Radioactive Ion Beams by the ISOL Technique, PhD. Thesis, UPC-ETSEIB / CERN. [2] J. Crank, The Mathematics of Diffusion, Clarendon Press (1956). [3] The TARGISOL Project, www.csic.es/targisolwww.csic.es/targisol [4] K. Torrance, E. Sparrow, Theory for off-specular reflection from rough surfaces, Journal of the Optical Society of America, 57 (1967) 1105-1114. [5] A. Siber, Theory of Thermal Energy Inert Atom Scattering from Surface Vibrations, Phd. Institute of Physics, Zagreb (2000). [6] U. Koester, Yields and Spectroscopy of Radioactive Isotopes at LOHENGRIN and ISOLDE, PhD thesis, Phys. Dpt. Technischen Universitaet Muenchen, [7] Persistance of Vision Pty. Ltd, www.povray.orgwww.povray.org [8] A. Andrighetto, MC Calculation in UCx Target at 40 MeV incident energy, Presentation at Orsay, 13/05/2005 [9] A. Andrighetto, M. Barbui, M. Cinusero, F. Gramengna, G. Prete (LNL), C. M. Antonucci, S.Cevolani, C. Petrovich (ENEA Bologna), M. Santana (CERN), Uranium Carbide Fision Disc Targets for the SPES Project, an Update, The European Phys. Jour. A (in preparation). DIFFUSION IN SOLIDS. RIBO-diffuse The first occurring process, and often the dominant one. Atoms diffuse driven by a ‘concentration repulsive force’[2]: RIBO-diffuse is a finite method code that computes diffusion for particles, fibers and foils with: Variable D, D(x) Time varying D, D(x,t) Pulsed beams. Source/sink terms. Additional features: invert the diffusion function [3] and sample diffusion times. EFFUSION IN POWDERS AND FIBERS Just like normal effusion, except that individual objects can’t be described geometrically. Instead, the media are taken as continue, and a statistical approach is used. An average flight path FP between collisions is fitted. Macro steps are used. The FP, D and sticking time are fitted against real data. For example, after fitting these results are obtained.